WO2024218207A1

WO2024218207A1 - Thieno[3,2-b]pyridine derivatives

Info

Publication number: WO2024218207A1
Application number: PCT/EP2024/060533
Authority: WO
Inventors: Cosimo Dolente; Hasane Ratni
Original assignee: F Hoffmann La Roche AG; Hoffmann La Roche Inc
Current assignee: F Hoffmann La Roche AG; Hoffmann La Roche Inc
Priority date: 2023-04-20
Filing date: 2024-04-18
Publication date: 2024-10-24
Anticipated expiration: 2025-10-20
Also published as: AR132478A1; TW202448451A

Abstract

The invention relates to a compound of formula (I) wherein R¹-R⁴ and A₁ are as defined in the description and in the claims. The compound of formula (I) can be used as a medicament.

Description

THIENO[3,2-B]PYRIDINE DERIVATIVES

The present invention relates to new organic compounds useful for therapy and/or prophylaxis in a mammal, and in particular to compounds that reduce the protein level of huntingtin (HTT) and which are useful in the treatment of Huntington’s disease.

In particular, the present invention relates to a compound of formula (I)

wherein

R¹ and R² are independently selected from hydrogen and alkyl; or R¹ and R² together with the carbon atom they are attached to, form cycloalkyl;

R³ is hydrogen, halogen, alkyl, alkoxy, haloalkyl or haloalkoxy;

R⁴ is hydrogen, alkyl or halogen; and

A¹ is -N- or -CH-; or a pharmaceutically acceptable salt thereof.

Huntington’s Disease (HD) is an inherited autosomal dominant neurodegenerative disease caused due to a CAG bases repeat expansion in the huntingtin (HTT) gene. Several lines of evidence indicate that the mutant HTT gene together with its gene product mHTT protein contributes to HD pathogenesis via a toxic gain of function mechanism.

The triplet repeat expansion in the exon 1 of the HTT gene translates into a polyglutamine repeat in the HTT protein which is prone to misfolding and aggregating in the cells. While the exact mechanisms of how mutant HTT disrupts cellular function is unclear, several processes ranging from interruption of RNA translation, toxic RNA species, protein aggregates, RNA translation, and stress granules have been implicated. At a neural circuit level, HD has been shown to affects deep brains structures like the striatum as well as cortical regions to different extents. Seminal mouse genetic experiments coupled with human imaging experiments point to a key role of cortico-striatal connections in the pathogenicity of HD (Wang et al., "Neuronal targets of mutant huntingtin genetic reduction to ameliorate Huntington’s disease pathogenesis in mice" Nature medicine 20.5 (2014): 536; Tabrizi et al.; "Potential endpoints for clinical trials in premanifest and early Huntington's disease in the TRACK-HD study: analysis of 24 month observational data." The Lancet Neurology 11.1 (2012): 42-53).

HD typically manifests around 30-50 years of age characterized by a multitude of symptoms spanning the motor, cognitive and affective domains eventually leading to death in 10- 20 years after the onset of motor symptoms. CAG repeat length negatively correlates with age of onset of motor symptoms, however this only accounts for 50-70% of the variance in age of onset. In an effort to identify genetic modifiers of age of onset in HD, Lee et al. (2019, Huntington's disease onset is determined by length of uninterrupted CAG, not encoded polyglutamine, and is modified by DNA maintenance mechanisms. Bioarxiv doi: https://doi.Org/10. l 101/529768) conducted a large GWAS (genome-wide association study) that has uncovered additional genetic modifiers of age of onset.

Various mouse models have been characterized to model aspects of HD. The YAC128 mice expressing the full length mutant HTT transgene with 128 CAG repeats, BACHD mice expressing the full length mutant HTT genomic sequence with 97 CAG/CAA repeats, the R6/2 mice expressing exon 1 of the mutant human HTT gene with 110-135 CAG repeats). In addition to these mice that express the human transgene, there are also a series of mouse models, like the frequently used Ql l l, the Q175 knock in mice where the expanded repeats are knocked-in in the context of the mouse HTT locus.

There are currently no disease modifying therapies for Huntington’s Disease while several are in development. The core disease process behind the symptomatology characterized by motor, cognitive and behavioral symptoms remains unmet by the various symptomatic treatments currently approved. Tetrabenazine and tiapride are currently approved for the treatment of motor symptoms namely HD-associated chorea. In addition, anticonvulsants, benzodiazepines, antidepressants, and antipsychotics are also used off-label to treat the motor, cognitive and psychiatric symptoms associated with HD.

Several therapeutic strategies targeting DNA and RNA are being investigated for HTT lowering (E. J. Wild, S. Tabrizi, Lancet Neurol. 2017 16(10): 837-847). HTT lowering is a promising therapeutic approach that aims to slow disease progression by getting at the core cause of Huntington’s Disease. HTT lowering is thought to be transformative when treated in the premanifest or manifest stages of disease onset, thus preventing major neurodegenerative processes in the brain. However, the challenge lies in identifying the patients at the right disease stage, as age of onset is quite variable across the population (S. J. Tabrizi, R. Ghosh, B. R. Leavitt, Neuron, 2019, 102(4), 899).

The current clinical approaches are mainly based on antisense oligonucleotides (ASOs). In addition, a few allele specific lowering strategies such as SNP (single-nucleotide polymorphism) based ASO and zinc finger based gene editing approaches are investigated. While the use of small molecules to lower HTT expression has been postulated, this strategy has not yet been validated and none has proved successful so far.

Small molecules provide an opportunity to allow for HTT lowering in the brain as well as the periphery. In addition, a small molecule modality allows access to patient populations that could be difficult to reach with modalities like ASOs or gene therapy.

There is thus the need for new compounds capable of lowering mHTT.

The applicant has surprisingly found that the compounds of the invention are active in lowering mHTT, as well as wild-type HTT, by modifying the splicing of said gene. In consequence, the compounds of the present invention are useful in the treatment of HD.

Importantly, the compounds of the present invention provide favourable selectivity over known off-targets of splicing modifiers, and thus a higher therapeutic window when compared with non-selective splicing modifiers. One known off-target of small molecule splice modifiers is for instance FOXM1 that is a key cell cycle regulator. Particular undesired splice variants of FOXM1 are comprising exon9 (also known as exon A2) insertions, such as for instance deltaC2 and the variant comprising full-length exon A2. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety.

In the present description the term “alkyl”, alone or in combination, signifies a linear or branched saturated hydrocarbon group of 1 to 8 carbon atoms, in particular of 1 to 6 carbon atoms and more particular of 1 to 4 carbon atoms. Examples of straight-chain and branched-chain C1-C8 alkyl groups are for instance methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert.-butyl, the isomeric pentyls, the isomeric hexyls, the isomeric heptyls and the isomeric octyls. Particular examples of “alkyl” are methyl, ethyl and isopropyl. Methyl and ethyl are particular examples of “alkyl” in the compound of formula (I).

The term “alkoxy” or “alkyloxy”, alone or in combination, signifies a group of the formula alkyl-O- in which the term "alkyl" has the previously given significance. Examples of alkoxy are for instance methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, sec-butoxy and tert.- butoxy. A particular example of “alkoxy” is methoxy.

The term “oxy”, alone or in combination, signifies the -O- group.

The terms “halogen” or “halo”, alone or in combination, signifies fluorine, chlorine, bromine or iodine and particularly fluorine, chlorine or bromine. One preferred example of halogen is fluorine. The term “halo”, in combination with another group, if not otherwise specified, denotes the substitution of said group with at least one halogen, particularly substituted with one to five halogens, particularly one to four halogens, i.e. one, two, three or four halogens.

The term “haloalkyl”, alone or in combination, denotes an alkyl group substituted with at least one halogen, particularly substituted with one to five halogens, particularly one to three halogens. Particular “haloalkyl” are fluoromethyl, trifluoromethyl, difluoromethyl, fluoroethyl, fluoropropyl and fluorobutyl. Further particular “haloalkyl” are difluoromethyl and tri fluoromethyl.

The term “pharmaceutically acceptable salt” refers to those salts which retain the biological effectiveness and properties of the free bases or free acids, which are not biologically or otherwise undesirable. The salts are formed with inorganic acids such as hydrochloric acid, hydrobromic acid, sulfuric acid, nitric acid, phosphoric acid, particularly hydrochloric acid, and organic acids such as formic acid, acetic acid, propionic acid, glycolic acid, pyruvic acid, oxalic acid, maleic acid, malonic acid, succinic acid, fumaric acid, tartaric acid, citric acid, benzoic acid, cinnamic acid, mandelic acid, methanesulfonic acid, ethanesulfonic acid, p-toluenesulfonic acid, salicylic acid, N-acetylcystein and trifluoroacetic acid. In addition these salts may be prepared form addition of an inorganic base or an organic base to the free acid. Salts derived from an inorganic base include, but are not limited to, the sodium, potassium, lithium, ammonium, calcium, magnesium salts. Salts derived from organic bases include, but are not limited to salts of primary, secondary, and tertiary amines, substituted amines including naturally occurring substituted amines, cyclic amines and basic ion exchange resins, such as isopropylamine, trimethylamine, diethylamine, triethylamine, tripropylamine, ethanolamine, lysine, arginine, N- ethylpiperidine, piperidine, polyamine resins. The compound of formula (I) can also be present in the form of zwitterions. Particularly preferred pharmaceutically acceptable salts of compounds of formula (I) are the salts formed with formic acid, trifluoroacetic acid or hydrochloric acid.

If one of the starting materials or compounds of formula (I) contain one or more functional groups which are not stable or are reactive under the reaction conditions of one or more reaction steps, appropriate protecting groups (as described e.g. in “Protective Groups in Organic Chemistry” by T. W. Greene and P. G. M. Wuts, 3rd Ed., 1999, Wiley, New York) can be introduced before the critical step applying methods well known in the art. Such protecting groups can be removed at a later stage of the synthesis using standard methods described in the literature. Examples of protecting groups are tert-butoxy carbonyl (Boc), trityl (Trt), 2, 4. dimethoxybenzyl (Dmb), 9-fluorenylmethyl carbamate (Fmoc), 2-trimethylsilylethyl carbamate (Teoc), carbobenzyl oxy (Cbz) and p-methoxybenzyloxycarbonyl (Moz). A particular example of a protecting group is tert-butoxy carbonyl (Boc).

A certain embodiment of the invention relates to the compound of formula (I) as described herein, or a pharmaceutically acceptable salt thereof, wherein at least one substituent comprises at least one radioisotope. Particular examples of radioisotopes are ²H, ³H, ¹³C, ¹⁴C and ¹⁸F.

Furthermore, the invention includes the compound of formula (I) as described herein, or a pharmaceutically acceptable salt thereof, wherein the compound comprises at least one radioisotope. Particular examples of radioisotopes are ²H, ³H, ¹³C, ¹⁴C and ¹⁸F. Furthermore, the invention includes all optical isomers, i.e. diastereoisomers, diastereomeric mixtures, racemic mixtures, all their corresponding enantiomers and/or tautomers as well as their solvates, wherever applicable, of the compound of formula (I).

The compound of formula (I) may contain one or more asymmetric centers and can therefore occur as racemates, racemic mixtures, single enantiomers, diastereomeric mixtures and individual diastereomers. Additional asymmetric centers may be present depending upon the nature of the various substituents on the molecule. Each such asymmetric center will independently produce two optical isomers and it is intended that all of the possible optical isomers and diastereomers in mixtures and as pure or partially purified compounds are included within this invention. The present invention is meant to encompass all such isomeric forms of these compounds. The independent syntheses of these diastereomers or their chromatographic separations may be achieved as known in the art by appropriate modification of the methodology disclosed herein. Their absolute stereochemistry may be determined by the x-ray crystallography of crystalline products or crystalline intermediates which are derivatized, if necessary, with a reagent containing an asymmetric center of known absolute configuration. If desired, racemic mixtures of the compounds may be separated so that the individual enantiomers are isolated. The separation can be carried out by methods well known in the art, such as the coupling of a racemic mixture of compounds to an enantiomerically pure compound to form a diastereomeric mixture, followed by separation of the individual diastereomers by standard methods, such as fractional crystallization or chromatography.

The term “asymmetric carbon atom” means a carbon atom with four different substituents. According to the Cahn-Ingold-Prelog Convention an asymmetric carbon atom can be of the “R” or “S” configuration.

The invention thus also relates in particular to:

A compound according to the invention, wherein R¹ and R² are both hydrogen; or R¹ and R² together with the carbon atom which they are attached to, form cycloalkyl;

A compound according to the invention, wherein R¹ and R² are both hydrogen; or R¹ and R² together with the carbon atom which they are attached to, form cyclopropyl; A compound according to the invention, wherein R¹ and R² are both hydrogen;

A compound according to the invention, wherein R¹ and R² together with the carbon atom which they are attached to, form cycloalkyl;

A compound according to the invention, wherein R¹ and R² together with the carbon atom which they are attached to, form cyclopropyl;

A compound according to the invention, wherein R³ is hydrogen, methyl, methoxy, fluoro, trifluoromethyl, difluoromethoxy or trifluoromethoxy;

A compound according to the invention, wherein R³ is hydrogen, methyl, fluoro or tri fluoromethyl;

A compound according to the invention, wherein R³ is trifluoromethyl;

A compound according to the invention, wherein R³ is difluoromethoxy or tri fluoromethoxy;

A compound according to the invention, wherein R³ is methoxy;

A compound according to the invention, wherein R³ is methyl;

A compound according to the invention, wherein R⁴ is hydrogen, methyl, fluoro or chloro;

A compound according to the invention, wherein R⁴ is methyl

A compound according to the invention, wherein R⁴ is chloro;

A compound according to the invention, wherein Ai is -N-;

A compound according to the invention, wherein Ai is -CH-;

A compound of formula (I) according the invention selected from

6-(8-methoxy-2-methyl-imidazo[l,2-b]pyridazin-6-yl)-2-(4-piperidyl)thieno[3,2- b]pyridine; 6-[2-methyl-8-(trifluoromethyl)imidazo[l,2-b]pyridazin-6-yl]-2-(4-piperidyl)thieno[3,2- b]pyridine;

2-(4-azaspiro[2.5]octan-7-yl)-6-(8-methoxy-2-methyl-imidazo[l,2-b]pyridazin-6- yl)thieno[3,2-b]pyridine;

6-(2,8-dimethylimidazo[l,2-b]pyridazin-6-yl)-2-(4-piperidyl)thieno[3,2-b]pyridine;

6-(2-methylimidazo[l,2-b]pyridazin-6-yl)-2-(4-piperidyl)thieno[3,2-b]pyridine;

6-(8-fluoro-2-methyl-imidazo[l,2-a]pyridin-6-yl)-2-(4-piperidyl)thieno[3,2-b]pyridine;

2-[(7S)-4-azaspiro[2.5]octan-7-yl]-6-(8-methoxy-2-methyl-imidazo[l,2-b]pyridazin-6- yl)thieno[3,2-b]pyridine; and

2-[(7R)-4-azaspiro[2.5]octan-7-yl]-6-(8-methoxy-2-methyl-imidazo[l,2-b]pyridazin-6- yl)thieno[3,2-b]pyridine; or a pharmaceutically acceptable salt thereof;

A compound of formula (I) according the invention selected from

6-(8-methoxy-2-methyl-imidazo[l,2-b]pyridazin-6-yl)-2-(4-piperidyl)thieno[3,2- b]pyridine;

6-[2-methyl-8-(trifluoromethyl)imidazo[l,2-b]pyridazin-6-yl]-2-(4-piperidyl)thieno[3,2- b]pyridine;

6-(2-methylimidazo[l,2-b]pyridazin-6-yl)-2-(4-piperidyl)thieno[3,2-b]pyridine;

6-(8-fluoro-2-methyl-imidazo[l,2-a]pyridin-6-yl)-2-(4-piperidyl)thieno[3,2-b]pyridine; 2-[(7S)-4-azaspiro[2.5]octan-7-yl]-6-(8-methoxy-2-methyl-imidazo[l,2-b]pyridazin-6- yl)thieno[3,2-b]pyridine;

2-[(7R)-4-azaspiro[2.5]octan-7-yl]-6-(8-methoxy-2-methyl-imidazo[l,2-b]pyridazin-6- yl)thieno[3,2-b]pyridine;

2-(4-Azaspiro[2.5]octan-7-yl)-6-[8-(difluoromethoxy)-2-methyl-imidazo[l,2-b]pyridazin- 6-yl]thieno[3,2-b]pyridine;

2-[(7R)-4-Azaspiro[2.5]octan-7-yl]-6-[8-(difluoromethoxy)-2-methyl-imidazo[l,2- b]pyridazin-6-yl]thieno[3,2-b]pyridine;

2-[(7S)-4-Azaspiro[2.5]octan-7-yl]-6-[8-(difluoromethoxy)-2-methyl-imidazo[l,2- b]pyridazin-6-yl]thieno[3,2-b]pyridine; and

2-(4-Azaspiro[2.5]octan-7-yl)-6-[2-methyl-8-(trifluoromethoxy)imidazo[l,2-b]pyridazin-6- yl]thieno[3,2-b]pyridine; or a pharmaceutically acceptable salt thereof.

In one embodiment of the invention the compound of formula (I) is

In one embodiment of the invention the compound of formula (I) is 2-(4-azaspiro[2.5]octan-7-yl)-6-(8-methoxy-2-methyl-imidazo[l,2-b]pyridazin-6- yl)thieno[3,2-b]pyridine, or a pharmaceutically acceptable salt thereof.

In one embodiment of the invention the compound of formula (I) is

6-(8-methoxy-2-methyl-imidazo[l,2-b]pyridazin-6-yl)-2-[rac-(7S)-4-azaspiro[2.5]octan-7- yl]thieno[3,2-b]pyridine, or a pharmaceutically acceptable salt thereof.

In one embodiment of the invention the compound of formula (I) is

6-(8-methoxy-2-methyl-imidazo[l,2-b]pyridazin-6-yl)-2-[rac-(7R)-4-azaspiro[2.5]octan-7- yl]thieno[3,2-b]pyridine, or a pharmaceutically acceptable salt thereof.

In one embodiment of the invention the compound of formula (I) is

2-[(7S)-4-azaspiro[2.5]octan-7-yl]-6-(8-methoxy-2-methyl-imidazo[l,2-b]pyridazin-6- yl)thieno[3,2-b]pyridine, or a pharmaceutically acceptable salt thereof.

In one embodiment of the invention the compound of formula (I) is

2-[(7R)-4-azaspiro[2.5]octan-7-yl]-6-(8-methoxy-2-methyl-imidazo[l,2-b]pyridazin-6- yl)thieno[3,2-b]pyridine, or a pharmaceutically acceptable salt thereof.

In one embodiment of the invention the compound of formula (I) is

2-[(7S)-4-azaspiro[2.5]octan-7-yl]-6-(8-methoxy-2-methyl-imidazo[l,2-b]pyridazin-6- yl)thieno[3,2-b]pyridine.

In one embodiment of the invention the compound of formula (I) is

2-[(7R)-4-azaspiro[2.5]octan-7-yl]-6-(8-methoxy-2-methyl-imidazo[l,2-b]pyridazin-6- yl)thieno[3,2-b]pyridine.

In one embodiment of the invention the compound of formula (I) is

2-[(7R)-4-azaspiro[2.5]octan-7-yl]-6-(8-methoxy-2-methyl-imidazo[l,2-b]pyridazin-6- yl)thieno[3,2-b]pyridine. In one embodiment of the invention the compound of formula (I) is 2-(4- Azaspiro[2.5]octan-7-yl)-6-[8-(difluoromethoxy)-2-methyl-imidazo[l,2-b]pyridazin-6- yl]thieno[3,2-b]pyridine, or a pharmaceutically acceptable salt thereof.

In one embodiment of the invention the compound of formula (I) is 2-(4- Azaspiro[2.5]octan-7-yl)-6-[8-(difluoromethoxy)-2-methyl-imidazo[l,2-b]pyridazin-6- yl]thieno[3,2-b]pyridine.

In one embodiment of the invention the compound of formula (I) is 2-[(7R)-4- Azaspiro[2.5]octan-7-yl]-6-[8-(difluoromethoxy)-2-methyl-imidazo[l,2-b]pyridazin-6- yl]thieno[3,2-b]pyridine.

In one embodiment of the invention the compound of formula (I) is 2-[(7S)-4- Azaspiro[2.5]octan-7-yl]-6-[8-(difluoromethoxy)-2-methyl-imidazo[l,2-b]pyridazin-6- yl]thieno[3,2-b]pyridine.

In one embodiment of the invention the compound of formula (I) is 2-[(7R)-4- Azaspiro[2.5]octan-7-yl]-6-[8-(difluoromethoxy)-2-methyl-imidazo[l,2-b]pyridazin-6- yl]thieno[3,2-b]pyridine, or a pharmaceutically acceptable salt thereof.

In one embodiment of the invention the compound of formula (I) is 2-[(7S)-4- Azaspiro[2.5]octan-7-yl]-6-[8-(difluoromethoxy)-2-methyl-imidazo[l,2-b]pyridazin-6- yl]thieno[3,2-b]pyridine, or a pharmaceutically acceptable salt thereof.

In one embodiment of the invention the compound of formula (I) is 2-(4- Azaspiro[2.5]octan-7-yl)-6-[2-methyl-8-(trifluoromethoxy)imidazo[l,2-b]pyridazin-6- yl]thieno[3,2-b]pyridine, or a pharmaceutically acceptable salt thereof.

The synthesis of the compound of formula (I) can, for example, be accomplished according following schemes. R'-R⁴ and Ai are as defined above, unless otherwise specified.

Scheme 1

The preparation of derivatives of general formula I, can be made according to the general scheme 1. A cyclization of tert-butyl 7V-(3-thienyl)carbamate (1) with 2-bromopropanedial (2) at elevated temperature afford the 6-bromothieno[3,2-b]pyridine intermediate 3. Intermediate 3 can be lithiated in a suitable solvent like tetrahydrofuran to give rise to the 6-bromo-2-iodo-thieno[3,2- b]pyridine intermediate 4. Intermediates of formula 7 are obtained according to methods known in the art, e.g. by consecutive treatment of a compound of a ketone of formula 5 with an organic base such as lithium diisopropylamide or lithium bis(trimethylsilyl)amide and an electrophilic reactant of formula 6. Boronic ester of formula 9 are obtained by borylation of intermediates 7 with bis(pinacolato)diboron (8). Suzuki coupling of 4 and 9 under suitable conditions gives rise to intermediates of formula 10. A subsequent Suzuki coupling of intermediate 10 with a suitable boronic acid 11 afforded intermediates of formula 12. The resulting intermediate 12 was then readily hydrogenated with Pd/C and H2 to afford derivatives 13. BOC-deprotection according to methods known in the art gives rise to compound of general formula I.

Scheme 2

The preparation of derivatives of general formula I, can alternatively be made according to the general scheme 2. A cyclization of N-(5-bromo-3-thienyl)carbamic acid tert-butyl ester (14) with 2-chloropropanedial (15) at elevated temperature afford the 2-bromo-6-chloro-thieno[3,2- b]pyridine intermediate 16. Suzuki coupling of 16 and 9 under suitable conditions gives rise to intermediates of formula 17. A subsequent Suzuki coupling of intermediate 17 with a suitable boronic acid 11 afforded intermediates of formula 12. Regarding boronic acid 11, pinacolatoboron and methyliminodiacetic acid (MID A) boronate are suitable boronic acids, as well as BF3K. The resulting intermediate 12 was then readily hydrogenated with Pd/C and H2 to afford derivatives 13. BOC-deprotection according to methods known in the art gives rise to compound of general formula I.

The invention thus also relates to a process for the preparation of a compound according to the invention, comprising at least one of the following steps:

(a) the reaction of a compound of formula (Bl)

with a compound of formula (B2)

in a suitable solvent in the presence of a base and a suitable palladium catalyst, wherein PG is a suitable protecting group and in -B(0R)2 each R is independently selected from hydrogen and alkyl, or -B(0R)2 is a suitable dioxaborolanyl, to arrive at a compound of fomula (B3)

(b) the hydrogenation of the compound of formula (B3), in a suitable solvent and in presence of hydrogen and a suitable catalyst to yield the compound of formula (B4)

(c) the reaction of the compound of formula (B4), in a suitable solvent and under suitable conditions to yield the compound of formula (I)

wherein in the above process, PG is a protecting group, Ai, Rl, R2 and R3 are as described herein.

In step (a), the solvent can be for instance 1,4-di oxane, acetonitrile, THF, DMF or mixtures of the mentioned solvents and water.

In step (a), the base can be for instance tri ethylamine, Na2CO3 or K2CO3.

In step (a), the palladium catalyst can be for instance Pd(dppf)C12 or XPhos Pd G3.

In step (a), the dioxaborolanyl is optionally substituted with one to four substituents independently selected from methyl, ethyl and isopropyl. In step (a), dioxaborolanyl can be for instance pinacolatoboron, methyliminodiacetic acid (MID A) boronate; in step (a) B(0R)2 can also be BF3K.

Preferentially, the reaction of step (a) is performed between around 70 to 130 °C, in particular between around 80 to around 120 °C, wherein the solvent is a mixture of 1,4-dioxane and water, the base is K2CO3 or tri ethylamine and the palladium catalyst is Pd(dppf)C12 or XPhos Pd G3.

In step (b), the solvent can be for instance EtOAc, EtOH, MeOH, THF or a mixture thereof.

In step (b), the catalyst can be for instance Pd/C, Pt/C or PtCF.

Preferentially, the reaction of step (b) is performed between around 10 to 70 °C, in particular between around 20 to around 60 °C, wherein the solvent is EtOAc and the catalyst is Pd/C.

In step (c), the solvent can be for instance 1,4-dioxane, EtOAc, THF, MeOH, EtOH or water or a mixture thereof. The solvent can also be DCM depending on the structure of the protecting group.

In step (c), suitable conditions can be for instance a suitable acid or a suitable base.

Preferentially, in step (c) the solvent is a suitable organic solvent such as for instance 1,4- dioxane or DCM, and the acid is HC1 or TFA.

Preferentially, in step (c) the solvent is a suitable organic solvent, and the base is suitable organic base such as for instance a primary or a secondary amine, in particular the base is piperidine.

In the above process, the protection group can be for instance BOC, TRT, FMOC, TEOC, DMB, CBZ or MOZ, in particular BOC.

The invention also relates to a compound according to the invention when manufactured according to a process of the invention.

The invention thus also relates in particular to:

A compound according to the invention for use as therapeutically active substance; A pharmaceutical composition comprising a compound according to the invention and a therapeutically inert carrier;

A compound according to the invention for use in the treatment or prophylaxis of a neurodegenerative disease;

A compound according to the invention for use in the treatment or prophylaxis of Huntington’s disease;

The use of a compound according to the invention for the treatment or prophylaxis of a neurodegenerative disease, in particular Huntington’s disease;

The use of a compound according to the invention for the preparation of a medicament for the treatment or prophylaxis of a neurodegenerative disease, in particular Huntington’s disease;

A method for the treatment or prophylaxis of a neurodegenerative disease, in particular Huntington’s disease, which method comprises administering an effective amount of a compound according to the invention to a patient in need thereof; and

A method for lowering mutant HTT, which method comprises administering an effective amount of a compound according to the invention to a patient in need thereof.

A certain embodiment of the invention relates to a pharmaceutical composition comprising the compound of formula (I) as described herein, or a pharmaceutically acceptable salt thereof, and a pharmaceutically acceptable auxiliary substance.

Furthermore, structures depicted herein are also meant to include compounds that differ only in the presence of one or more isotopically enriched atoms. For example wherein one or more hydrogen atoms are replaced by deuterium (2H), or one or more carbon atoms are replaced by a 13C- or 14C-enriched carbon are within the scope of this invention.

Furthermore, the invention includes all optical isomers, i.e. diastereoisomers, diastereomeric mixtures, racemic mixtures, all their corresponding enantiomers and/or tautomers as well as their solvates, wherever applicable, of the compound of formula (I). The compound of formula (I) may contain one or more asymmetric centers and can therefore occur as racemates, racemic mixtures, single enantiomers, diastereomeric mixtures and individual diastereomers. Additional asymmetric centers may be present depending upon the nature of the various substituents on the molecule. Each such asymmetric center will independently produce two optical isomers and it is intended that all of the possible optical isomers and diastereomers in mixtures and as pure or partially purified compounds are included within this invention. The present invention is meant to encompass all such isomeric forms of these compounds. The independent syntheses of these diastereomers or their chromatographic separations may be achieved as known in the art by appropriate modification of the methodology disclosed herein. Their absolute stereochemistry may be determined by the x-ray crystallography of crystalline products or crystalline intermediates which are derivatized, if necessary, with a reagent containing an asymmetric center of known absolute configuration. If desired, racemic mixtures of the compounds may be separated so that the individual enantiomers are isolated. The separation can be carried out by methods well known in the art, such as the coupling of a racemic mixture of compounds to an enantiomerically pure compound to form a diastereomeric mixture, followed by separation of the individual diastereomers by standard methods, such as fractional crystallization or chromatography.

In the embodiments, where optically pure enantiomers are provided, optically pure enantiomer means that the compound contains > 90 % of the desired isomer by weight, particularly > 95 % of the desired isomer by weight, or more particularly > 99 % of the desired isomer by weight, said weight percent based upon the total weight of the isomer(s) of the compound. Chirally pure or chirally enriched compounds may be prepared by chirally selective synthesis or by separation of enantiomers. The separation of enantiomers may be carried out on the final product or alternatively on a suitable intermediate.

Also an embodiment of the present invention is a compound of formula (I) as described herein, when manufactured according to any one of the described processes.

The compound of formula (I) or a pharmaceutically acceptable salt thereof can be used as a medicament (e.g. in the form of a pharmaceutical preparation). The pharmaceutical preparation can be administered internally, such as orally (e.g. in the form of tablets, coated tablets, dragees, hard and soft gelatin capsules, solutions, emulsions or suspensions), nasally (e.g. in the form of nasal sprays), rectally (e.g. in the form of suppositories) or topical ocularly (e.g. in the form of solutions, ointments, gels or water soluble polymeric inserts). However, the administration can also be effected parenterally, such as intramuscularly, intravenously, or intraocularly (e.g. in the form of sterile injection solutions).

The compound of formula (I) or a pharmaceutically acceptable salt thereof can be processed with pharmaceutically inert, inorganic or organic adjuvants for the production of tablets, coated tablets, dragees, hard gelatin capsules, injection solutions or topical formulations Lactose, corn starch or derivatives thereof, talc, stearic acid or its salts etc. can be used, for example, as such adjuvants for tablets, dragees and hard gelatin capsules.

Suitable adjuvants for soft gelatin capsules, are, for example, vegetable oils, waxes, fats, semi-solid substances and liquid polyols, etc.

Suitable adjuvants for the production of solutions and syrups are, for example, water, polyols, saccharose, invert sugar, glucose, etc.

Suitable adjuvants for injection solutions are, for example, water, alcohols, polyols, glycerol, vegetable oils, etc.

Suitable adjuvants for suppositories are, for example, natural or hardened oils, waxes, fats, semi-solid or liquid polyols, etc.

Suitable adjuvants for topical ocular formulations are, for example, cyclodextrins, mannitol or many other carriers and excipients known in the art.

Moreover, the pharmaceutical preparation can contain preservatives, solubilizers, viscosityincreasing substances, stabilizers, wetting agents, emulsifiers, sweeteners, colorants, flavorants, salts for varying the osmotic pressure, buffers, masking agents or antioxidants. The pharmaceutical preparation can also contain still other therapeutically valuable substances.

The dosage can vary in wide limits and will be fitted to the individual requirements in each particular case. In general, in the case of oral administration a daily dosage of about 0.1 mg to 20 mg per kg body weight, preferably about 0.5 mg to 4 mg per kg body weight (e.g. about 300 mg per person), divided into preferably 1-3 individual doses, which can consist, for example, of the same amounts, should it be appropriate. In the case of topical administration, the formulation can contain 0.001% to 15% by weight of medicament and the required dose, which can be between 0.1 and 25 mg in can be administered either by single dose per day or per week, or by multiple doses (2 to 4) per day, or by multiple doses per week It will, however, be clear that the upper or lower limit given herein can be exceeded when this is shown to be indicated.

Pharmaceutical Compositions

The compound of formula (I) or a pharmaceutically acceptable salt thereof can be used as a therapeutically active substance, e.g. in the form of a pharmaceutical preparation. The pharmaceutical preparation can be administered orally, e.g. in the form of tablets, coated tablets, dragees, hard and soft gelatin capsules, solutions, emulsions or suspensions. The administration can, however, also be effected rectally, e.g. in the form of suppositories, or parenterally, e.g. in the form of injection solutions.

The compound of formula (I) or a pharmaceutically acceptable salt thereof can be processed with pharmaceutically inert, inorganic or organic carriers for the production of a pharmaceutical preparation. Lactose, corn starch or derivatives thereof, talc, stearic acids or its salts and the like can be used, for example, as such carriers for tablets, coated tablets, dragees and hard gelatin capsules. Suitable carriers for soft gelatin capsules are, for example, vegetable oils, waxes, fats, semi-solid and liquid polyols and the like. Depending on the nature of the active substance no carriers are however usually required in the case of soft gelatin capsules. Suitable carriers for the production of solutions and syrups are, for example, water, polyols, glycerol, vegetable oil and the like. Suitable carriers for suppositories are, for example, natural or hardened oils, waxes, fats, semi- liquid or liquid polyols and the like.

The pharmaceutical preparation can, moreover, contain pharmaceutically acceptable auxiliary substances such as preservatives, solubilizers, stabilizers, wetting agents, emulsifiers, sweeteners, colorants, flavorants, salts for varying the osmotic pressure, buffers, masking agents or antioxidants. They can also contain still other therapeutically valuable substances.

Medicaments containing a compound of formula (I) or a pharmaceutically acceptable salt thereof and a therapeutically inert carrier are also provided by the present invention, as is a process for their production, which comprises bringing a compound of formula (I) and/or pharmaceutically acceptable salts thereof and, if desired, one or more other therapeutically valuable substances into a galenical administration form together with one or more therapeutically inert carriers.

The dosage can vary within wide limits and will, have to be adjusted to the individual requirements in each particular case. In the case of oral administration the dosage for adults can vary from about 0.01 mg to about 1000 mg per day of a compound of general formula (I) or of the corresponding amount of a pharmaceutically acceptable salt thereof. The daily dosage may be administered as single dose or in divided doses and, in addition, the upper limit can also be exceeded when this is found to be indicated.

The following examples illustrate the present invention without limiting it, but serve merely as representative thereof. The pharmaceutical preparation conveniently contains about 1-500 mg, particularly 1-100 mg, of a compound of formula (I). Examples of compositions according to the invention are:

Example A

Tablets of the following composition are manufactured in the usual manner:

Table 1 : possible tablet composition

Manufacturing Procedure

1. Mix ingredients 1, 2, 3 and 4 and granulate with purified water.

2. Dry the granules at 50°C.

3. Pass the granules through suitable milling equipment.

4. Add ingredient 5 and mix for three minutes; compress on a suitable press.

Example B-l

Capsules of the following composition are manufactured:

Table 2: possible capsule ingredient composition

Manufacturing Procedure

1. Mix ingredients 1, 2 and 3 in a suitable mixer for 30 minutes.

2. Add ingredients 4 and 5 and mix for 3 minutes.

3. Fill into a suitable capsule.

The compound of formula (I), lactose and corn starch are firstly mixed in a mixer and then in a comminuting machine. The mixture is returned to the mixer; the talc is added thereto and mixed thoroughly. The mixture is filled by machine into suitable capsules, e.g. hard gelatin capsules.

Example B-2

Soft Gelatin Capsules of the following composition are manufactured:

Table 3: possible soft gelatin capsule ingredient composition

Table 4: possible soft gelatin capsule composition

Manufacturing Procedure

The compound of formula (I) is dissolved in a warm melting of the other ingredients and the mixture is filled into soft gelatin capsules of appropriate size. The filled soft gelatin capsules are treated according to the usual procedures. Example C

Suppositories of the following composition are manufactured:

Table 5: possible suppository composition

Manufacturing Procedure

The suppository mass is melted in a glass or steel vessel, mixed thoroughly and cooled to 45°C. Thereupon, the finely powdered compound of formula (I) is added thereto and stirred until it has dispersed completely. The mixture is poured into suppository moulds of suitable size, left to cool; the suppositories are then removed from the moulds and packed individually in wax paper or metal foil.

Example D

Injection solutions of the following composition are manufactured:

Table 6: possible injection solution composition

Manufacturing Procedure

The compound of formula (I) is dissolved in a mixture of Polyethylene Glycol 400 and water for injection (part). The pH is adjusted to 5.0 by acetic acid. The volume is adjusted to 1.0 ml by addition of the residual amount of water. The solution is filtered, filled into vials using an appropriate overage and sterilized.

Example E

Sachets of the following composition are manufactured:

Table 7: possible sachet composition

Manufacturing Procedure The compound of formula (I) is mixed with lactose, microcrystalline cellulose and sodium carboxymethyl cellulose and granulated with a mixture of polyvinylpyrrolidone in water. The granulate is mixed with magnesium stearate and the flavoring additives and filled into sachets.

Examples

Abbreviations:

AcOEt: ethyl acetate; AcOH: acetic acid; ACN: acetonitrile; DCM: dichloromethane; DMAP: 4- dimethylaminopyridine; DMEM: dulbecco’s modified eagle medium; DMSO: dimethyl sulfoxide; ES+: positive electrospray ionization; EtOAc: ethyl acetate; EtOH: ethanol; FA: formic acid; FAM: fluorescein amidite fluorophore; FBS: fetal bovine serum; HEX: hexachlorofluorescin fluorophore; high performance liquid chromatography; HTRF : homogeneous time resolved fluorescence ; IPA: isopropyl alcohol; LDA: lithium diisopropylamide; LF: long form; MeOH: methanol; MS: mass spectrometry; NF: normal form; PBS: phosphate-buff ered saline; PCR: polymerase chain reaction; PPTS: pyridinium p-toluene sulfonate; QPCR: quantitative PCR; RM: reaction mixture; RT: retention time; RT-qPCR: reverse transcription quantitative PCR; TEA: tri ethyl amine; TFA: trifluoroacetic acid; THF: tetrahydrofuran.

The following examples are provided for illustration of the invention. They should not be considered as limiting the scope of the invention, but merely as being representative thereof.

Intermediates

Preparation of the central core intermediate 6-bromo-2-iodothieno[3,2-b]pyridine

Step 1: 6-bromothieno[3,2-b]pyridine 1 A mixture of tert-butyl N-(3-thienyl)carbamate (CAS No: 19228-91-2) (20.0 g, 100.37 mmol, 1.0 eq) and 2-bromomalonaldehyde (16.67 g, 110.4 mmol, 1.1 eq) in acetic acid (200 mL) was stirred at 100 °C for 20 hours. The reaction was concentrated to dryness and the residue was taken into EtOAc, the organics was washed with aqueous Na2CC>3, and saturated brine. The organics phase was then separated and dried (MgSCL) before concentration. The crude was purified by flash column chromatography (eluting with 0~80 %EtOAc in Hexane) to afford 6-bromothieno[3,2- b]pyridine (3.88 g, 18.12 mmol, 18.06% yield) as a light yellow solid. MS [M+H]⁺: 214.1.

Step 2: 6-bromo-2-iodo-thieno [3, 2-b] pyridine

The solution of 6-bromothieno[3,2-b]pyridine (3.88 g, 18.12 mmol, 1.0 eq) in THF (20 mL) was cooled to -78 °C, then LDA (10.87 mL, 21.75 mmol, 1.2 eq) was dropwise added to above solution under nitrogen atmosphere, the mixture was stirred for further 0.5 hour, a solution of iodine (5.52 g, 21.75 mmol, 1.2 eq) in THF (2 mL) was dropwise added. The reaction mixture was allowed warm to room temperature and stirred for 1 hour, then EtOAc was added to the mixture followed by the addition of H2O. The aqueous layer was extracted with EtOAc and the combined organic layers were dried (Na2SO4), filtered and concentrated, the residue was purified by flash column chromatography (eluting with 0~60 % EtOAc in Hexane) to get 6-bromo-2-iodo-thieno[3,2- b]pyridine (3.3 g, 9.71 mmol, 53.56% yield) as a light yellow solid. MS [M+H]⁺: 339.9.

Preparation of the central core intermediate 2-bromo-6-chloro-thieno[3,2-b]pyridine

To a solution of N-(5-bromo-3-thienyl)carbamic acid tert-butyl ester (5 g, 17.97 mmol, 1.000 eq) (CAS-Nr: 494833-75-9) in methanol (12.5 mL) was added 4 M HC1 in 1,4-dioxane (53.92 g, 44.94 mL, 179.75 mmol, 10.000 eq) at RT. Stirring was continued overnight. The solvent was removed in vacuo and glacial acetic acid (50 mL) added, followed by 2-chloromalonaldehyde (2.11 g, 19.77 mmol, 1.100 eq) (CAS Nr: 36437-19-1). The mixture was heated at reflux and stirred for 2 h. The solvents were evaporated and the residue was partitioned between dichloromethane (50 ml) and IM Na2CO3 sol (30 ml). The layers were separated. The aq layer was extracted with two 50-ml portions of dichloromethane. The combined organic layers were dried over sodium sulfate, filtered and concentrated in vacuo to give the crude title compound. Purification by flash-chromatography with n-heptane / ethyl acetate as eluent, gave the title compound (2.05 g; 34%) as an off-white solid with a purity of 74%. MS [M+H]+: 249.8, 251.8

Preparation of boronic esters and/or acids

Those derivatives were ultimately obtained as either a boronic ester, boronic acid or a mixture thereof and used directly in the subsequent step.

Boronic ester 1

2,8-dimethyl-6-(4,4,5,5-tetramethyl-l,3,2-dioxaborolan-2-yl)imidazo[l,2-b]pyridazine

Prepared according to WO2019/057740

Boronic ester 2

8-methoxy-2-methyl-6-(4,4,5,5-tetramethyl-l,3,2-dioxaborolan-2-yl)imidazo[l,2- bjpyridazine

Step 1 : Preparation of 8-bromo-6-chloro-2-methyl-imidazoll,2-b1pyridazine

To a solution of (4-bromo-6-chloro-pyridazin-3-yl)amine (CAS No: 446273-59-2) (2000 mg, 9.6 mmol) and PPTS (241 mg, 0.96 mmol) in isopropanol (19 mL) was added l-bromo-2,2-dimethoxy- propane (2.11 g, 1.56 mL, 11.5 mmol) at room temperature. The reaction mixture was heated at reflux for 30 hours. After cooling down to room temperature, the mixture was partitioned between ethyl acetate (50 ml) and IM ISfeCCh sol (30 ml). The layers were separated, and the organic layer was washed with one 30-ml portion of brine and dried over sodium sulfate, filtered and concentrated in vacuo to give the crude title compound (2.37 g, 92% yield) as light brown solid with a purity of 92%, which was used without further purification. MS (ES+) m/z 246.0-248.0 [(M+H)⁺],

Step 2: Preparation of 6-chloro-8-methoxy-2-methyl-imidazo|T,2-b]pyridazine:

To a solution of 8-bromo-6-chloro-2-methyl-imidazo[l,2-b]pyridazine (500 mg, 2.03 mmol) and cesium carbonate (1.4 g, 4.3 mmol) in acetonitrile (10 mL) was added MeOH (400 pL, 9.89 mmol) at room temperature and stirring was continued for 4 hours. The mixture was partitioned between ethyl acetate (30 mL) and water (30 mL). The combined organic layer was washed with one 30- mL portion of brine, dried over sodium sulfate, filtered and concentrated in vacuo. Purification by flash chromatography gave 6-chloro-8-methoxy-2-methyl-imidazo[l,2-b]pyridazine (337 mg; 84% yield) as a white solid. MS (ES+) m/z 198.0 [(M+H)⁺],

Step 3: Preparation of 8-methoxy-2-methyl-6-(4A5,5-tetramethyl-L3,2-dioxaborolan-2- yl)imidazorL2-b]pyridazine:

To a mixture of 6-chloro-8-methoxy-2-methyl-imidazo[l,2-b]pyridazine (118 mg, 0.597 mmol), bis(pinacolato)diboron (CAS No: 73183-34-3) (151.5 mg, 0.597 mmol, 1 eq) and potassium acetate (150.48 mg, 1.53 mmol) in 1,4-dioxane (1.2 mL) was added of XPhos Pd G4 (CAS No: 1599466-81-5) (22 mg, 0.026 mmol). The reaction mixture was heated at 100 °C for 1 hour. The reaction mixture was cooled to room temperature and diluted with ethyl acetate (5-10 mL). The solids were removed by filtration. The filtrate was concentrated in vacuo to give the crude title compound which was used directly in the next step without further purification. The obtained product could either be present as a boronic ester, boronic acid or mixtures thereof.

Boronic ester 3

2-methyl-6-(4,4,5,5-tetramethyl-l,3,2-dioxaborolan-2-yl)-8-(trifluoromethyl)imidazo[l,2- bjpyridazine

Stepl : Preparation of r6-chloro-4-(trifluoromethyl)pyridazin-3-yl1amine:

A mixture of 3,6-dichloro-4-(trifluoromethyl)pyridazine (9.95 g, 45.86 mmol, 1.000 eq) and 25% aqueous ammonia solution (31.24 g, 39.69 mL, 458.57 mmol, 10.000 eq) in 1,4-dioxane (100 ml) was heated at 50 °C for 15 hours. The mixture was partitioned between ethyl acetate (200 ml) and water (200 ml). The layers were separated. The aqueous layer was extracted with one 200-ml portion of ethyl acetate. The combined organic layers were washed with one 200-ml portion of brine dried over sodium sulfate, filtered and concentrated in vacuo to give the crude title compound. Purification by flash-chromatography with n-heptane / ethyl acetate as eluent gave the title compound (5.75 g, 63%) as white solid. MS (ES+) m/z 198 [(M+H)⁺],

Step 2: Preparation of 6-chloro-2-methyl-8-(trifluoromethyl)imidazolL2-b1pyridazine:

In a 10 mL round bottom flask, equipped with a magnetic stirrer bar, reflux condenser and N2-inlet bubbler, [6-chloro-4-(trifluoromethyl)pyridazin-3-yl]amine (94 mg, 0.476 mmol) and pyridinium /?-toluene sulfonate (11.9 mg, 0.048 mmol) were combined with isopropanol (2 mL). l-bromo-2,2- dimethoxy-propane (104.51 mg, 77.13 uL, 0.571 mmol, 1.2 eq) was added and the colorless solution was stirred 24 hours at 75 °C. The resulting dark-brown reaction mixture was cooled to room temperature and diluted with EtOAc (10 mL) and washed with a saturated aqueous NaHCOs- solution (10 mL). Organic layer was separated and dried over sodium sulfate, filtered off and concentrated in vacuo. The crude (120 mg brownish viscous oil) was purified by column chromatography yielding 6-chloro-2-methyl-8-(trifluoromethyl)imidazo[l,2-b]pyridazine (46 mg, 34% yield) as light yellow solid. MS (ES+) m/z 236.1 [(M+H)⁺],

Step 3: Preparation of 2-methyl-6-(4A5,5-tetramethyl-L3,2-dioxaborolan-2-yl)-8- (trifluoromethyl)imidazolL2-b1pyridazine:

In a dry/ Argon flushed 20 mL microwave tube with a magnetic stirrer bar and a cap-septum, 6- chloro-2-methyl-8-(trifluoromethyl)imidazo[l,2-b]pyridazine (300 mg, 1.2 mmol), bis(pinacolato)diboron (364.7 mg, 1.44 mmol) and potassium acetate (352.42 mg, 3.59 mmol) were combined with 1,4-dioxane (12 mL). The yellowish fine suspension was stirred and degassed with Argon for 10-15 minutes before tetrakis(triphenylphosphine)palladium (CAS No: 14221-01-3) (69.1 mg, 0.060 mmol) was added. The vial was sealed and stirred in a heating block (Temperature: 100 °C) for 22 hours. Further addition of tetrakis(triphenylphosphine)palladium (69 mg, 0.060 mmol), after 90 minutes, 3.5 hours and 6 hours. The reaction was cooled to room temperature, filtered off and concentrated in vacuo. The amber viscous oil was purified by column chromatography to give 2-methyl-6-(4,4,5,5-tetramethyl-l,3,2-dioxaborolan-2-yl)-8- (trifluoromethyl)imidazo[l,2-b]pyridazine (428 mg, 48%) as yellow viscous oil. The obtained product could either be present as a boronic ester, boronic acid or mixtures thereof.

Boronic ester 4

2-methyl-6-(4,4,5,5-tetramethyl-l,3,2-dioxaborolan-2-yl)imidazo[l,2-b]pyridazine

Prepared according to WO2015/173181

Boronic ester 5

8-fluoro-2-methyl-6-(4,4,5,5-tetramethyl-l,3,2-dioxaborolan-2-yl)imidazo[l,2-a]pyridine

Prepared according to WO2022/194802 Exemplified compounds of the compound of formula (I)

Example 1

6-(8-Methoxy-2-methyl-imidazo [1 ,2-b] pyridazin-6-yl)-2-(4-piperidyl)thieno [3,2-b] pyridine

Step 1: 8-bromo-6-chloro-2-methylimidazo[l,2-b]pyridazine

To a solution of 4-bromo-6-chloro-pyridazin-3-amine (CAS No: 446273-59-2) (5.0 g, 23.99 mmol, 1.0 eq) and pyridinium p-toluene sulfonate (0.6 g, 2.4 mmol, 0.1 eq) in IPA (50 mL) was added 1- bromo-2,2-dimethoxypropane (5.27 g, 28.79 mmol, 1.2 eq) at room temperature. The mixture was refluxed for 18 hours. The mixture was partitioned between ethyl acetate (200 ml) and IM Na2CCh aq (20 ml). The organic phase was separated, then washed with 30 ml brine, dried over sodium sulfate, filtered and concentrated. The residue was purified with silica gel column chromatography (diluting with EtOAc/hexane=l : l) to afford 8-bromo-6-chloro-2-methyl-imidazo[l,2-b] pyridazine (4.3 g, 17.44 mmol, 72.73% yield) as a yellow solid. [M+H]⁺=246.

'H NMR (400 MHz, DMSO) 1H NMR (400 MHz, DMSO) 8 8.23 (s, 1H), 7.85 (s, 1H), 2.40 (s, 3H).

Step 2: 6-chloro-8-methoxy-2-methylimidazo[l,2-b]pyridazine

To a mixture of 8-bromo-6-chloro-2-methyl-imidazo[l,2-b]pyridazine (4.3 g, 17.44 mmol, 1.0 eq) and CS2CO3 (12.54 g, 38.34 mmol, 2.2 eq) in ACN (50 mL) was added MeOH (2.80 g, 87.40 mmol, 5.0 eq) at room temperature. The mixture was stirred at room temperature for 16 hours. Then the solvent evaporated, the residue was diluted with ethyl acetate (100 ml), washed with water (100 ml), dried over sodium sulfate, filtered and concentrated, then the crude was purified by flash chromatography (diluting with EtOAc/hexane=2: l) to give 6-chloro-8-methoxy-2-methyl- imidazo[l,2-b]pyridazine (2.5 g, 12.65 mmol, 72.76% yield) as an off-white solid. [M+H]⁺=198.

Step 3: (8-methoxy-2-methylimidazo[l,2-b]pyridazin-6-yl)boronic acid A suspension of 6-chloro-8-methoxy-2-methyl-imidazo[l,2-b]pyridazine (2.5 g, 12.65 mmol, 1.0 eq), bis(pinacolato)diboron (3.85 g, 15.18 mmol, 1.2 eq), Potassium Acetate (2.37 mL, 37.95 mmol, 3.0 eq) and Xphos-Pd-G4 (816.43 mg, 0.95 mmol, 0.08 eq) in 1,4-dioxane (30 mL) was stirred at 100 °C for 3 hours under nitrogen atmosphere. The solvent was concentrated and the residue was purified by prep-HPLC (ACN-H2O, Gradient: 0-30%) to afford the (8-methoxy-2- methylimidazo[l,2-b]pyridazin-6-yl)boronic acid (1.2 g, 5.79 mmol, 45.80% yield) as an off-white solid. [M+H]⁺=208.

Step 4: tert-butyl 4-(6-bromothieno[3,2-b]pyridin-2-yl)-3,6-dihydro-2H-pyridine-l- carboxylate

To a solution of 6-bromo-2-iodo-thieno[3,2-b]pyridine (2.5 g, 7.35 mmol, 1.0 eq), l-N-BOC-4- (4,4,5,5-tetramethyl-[l,3,2]dioxaborolan-2-yl)-3,6-dihydro-2H-pyridine (CAS No: 286961-14-6) (2.27 g, 7.35 mmol, 1.0 eq) and Na2COs (1.56 g, 14.71 mmol, 2.0 eq) in Water (5 mL) / Toluene (25 mL) / Ethanol (25 mL) was added Pd(PPh3)4 (849.75 mg, 0.74 mmol, 0.1 eq), the mixture was stirred at 70 °C for 10 hours under nitrogen atmosphere. The mixture was cooled and then dilute with water (200 mL), extracted with DCM (100 mL*2), the organics were washed with brine (100 mL), dried over anhydrous Na2SO4, filtered and concentrated, the residue was purified by silica gel column chromatography (eluting with 0-30% EtOAc in hexane) to afford tert-butyl 4-(6- bromothieno[3,2-b]pyri din-2 -yl)-3,6-dihydropyri dine- l(2H)-carboxylate (1.8 g, 4.55 mmol, 61.92% yield) as white solid. [M+H]⁺= 395.

Step 5: tert-butyl 4-(6-(8-methoxy-2-methylimidazo[l,2-b]pyridazin-6-yl)thieno[3,2-b] pyri- din-2-yl)-3,6-dihydropyridine-l(2H)-carboxylate

A solution of tert-butyl 4-(6-bromothieno[3,2-b]pyridin-2-yl)-3,6-dihydro-2H-pyridine-l- carboxylate (500.0 mg, 1.26 mmol, 1.0 eq), (8-methoxy-2-methyl-imidazo[l,2-b]pyridazin-6- yl)boronic acid (785.42 mg, 3.79 mmol, 3.0 eq), K2CO3 (523.64 mg, 3.79 mmol, 3.0 eq) and Pd(dppf)C12 (CAS No: 72287-26-4) (92.46 mg, 0.13 mmol, 0.1 eq) in 1,4-dioxane (10 mL) and water (2.5 mL) was stirred at 90 °C for 10 hours under nitrogen atmosphere. The solvent was evaporated and the residue was purified by silica gel column chromatography (EtOAc/hexane =1 : 1) to afford tert-butyl 4-(6-(8-methoxy-2-methylimidazo[l,2-b]pyridazin-6-yl)thieno[3,2-b]pyridin- 2-yl)-3,6-dihydropyridine-l(2H)-carboxylate (350 mg, 0.73 mmol, 57.94%) as a light yellow solid. [M+H]⁺= 478.

Step 6: tert-butyl 4-(6-(8-methoxy-2-methylimidazo[l,2-b]pyridazin-6-yl)thieno[3,2-b] pyri- din-2-yl)piperidine-l-carboxylate

To a solution of tert-butyl 4-[6-(8-methoxy-2-methyl-imidazo[l,2-b]pyridazin-6-yl)thieno[3,2- b]pyridin-2-yl]-3,6-dihydro-2H-pyridine-l-carboxylate (350.0 mg, 0.73 mmol, 1.0 eq) in EtOAc (20 mL) was added Pd/C (350.0 mg, 10%). The resulting mixture was charged into hydrogen and stirred for 48 hours at 50 °C under 1.0 atm. The mixture were filtered and the filtrate was concentrated, the residue was purified by silica gel column chromatography (EtOAc/Hexane=2:l) to afford tert-butyl 4-[6-(8-methoxy-2-methyl-imidazo [l,2-b]pyridazin-6-yl)thieno[3,2-b]pyridin- 2-yl]piperidine-l-carboxylate (300.0 mg, 0.63 mmol, 85.36% yield) as yellow solid. [M+H]⁺= 480.

Step 7 : 6-(8-Methoxy-2-methyl-imidazo [1 ,2-b] pyridazin-6-yl)-2-(4-piperidyl)thieno [3,2- b] pyridine formic acid

To a solution of tert-butyl 4-[6-(8-methoxy-2-methyl-imidazo[l,2-b]pyridazin-6-yl)thieno[3,2- b]pyridin-2-yl]piperidine-l-carboxylate (300.0 mg, 0.63 mmol, 1.0 eq) in DCM (6 mL) was added HC1 in dioxane (3.0 mL, 12.0 mmol, 14.39 eq, 4 M), the mixture was stirred at 25 °C for 1 hour. Then the solvent was concentrated and the residue was purified by prep-HPLC (column: Gemini 5p C18 150 x 21.2 mm, ACN-H2O(0.1%FA) ) to afford 6-(8-methoxy-2-methyl-imidazo[l,2- b]pyridazin-6-yl)-2-(4-piperidyl)thieno[3,2-b]pyridine (120.1 mg, 0.28 mmol, 31.42% yield) as off-white solid. [M+H]⁺= 380.

'H NMR (400 MHz, DMSO) 8 9.29 (d, J = 2.1 Hz, 1H), 9.07 (d, J = 1.7 Hz, 1H), 8.33 (s, 1H), 8.03 (d, J = 0.8 Hz, 1H), 7.45 (s, 1H), 7.32 (s, 1H), 4.16 (s, 3H), 3.26 (d, J = 12.0 Hz, 3H), 2.89 (t, J = 11.5 Hz, 2H), 2.37 (s, 3H), 2.12 (t, J = 15.6 Hz, 2H), 1.81 (d, J = 9.3 Hz, 2H).

Example 2

6- [2-Methyl-8-(trifluoromethyl)imidazo [1 ,2-b] pyridazin-6-yl]-2-(4-piperidyl)thieno [3,2- b] pyridine

Step 1 : 4- [6- [2-methyl-8-(trifluoromethyl)imidazo [1 ,2-b] pyridazin-6-yl] thieno [3,2- b]pyridin-2-yl]-3,6-dihydro-2H-pyridine-l-carboxylic acid tert-butyl ester

To a mixture of [2-methyl-8-(trifluoromethyl)imidazo[l,2-b]pyridazin-6-yl]boronic acid (702 mg, 2.87 mmol, 2.000 eq; boronic ester 3), 4-(6-chlorothieno[3,2-b]pyridin-2-yl)-3,6-dihydro-2H- pyridine-1 -carboxylic acid tert-butyl ester (503 mg, 1.43 mmol, 1.000 eq, intermediate 17 wherein R¹ and R² are hydrogen) and potassium carbonate (792 mg, 5.73 mmol, 4.000 eq) in acetonitrile (6 mL) and water (0.7 mL) was added l,T-bis(diphenylphosphino)ferrocene-palladium(II)di chloride di chloromethane complex (CAS No: 72287-26-4) (119 mg, 0.144 mmol, 0.100 eq) at room temperature. The reaction mixture was heated in a sealed tube at 95 °C (heat-on plate of 95 °C) and stirred for 1.5 hours. The mixture was partitioned between ethyl acetate (70 ml) and IM NaHCCL sol (40 ml). The layers were separated. The aqueous layer was extracted with two 50-ml portions of ethyl acetate. The combined organic layers were washed with one 30-ml portion of brine and concentrated in vacuo. The crude material was purified by flash chromatography to give the title compound (135 mg, 18 %) as a yellow solid with a purity of 100 %. [M+H]⁺= 516.2

Step 2 : 4- [6- [2-methyl-8-(trifluoromethyl)imidazo [1 ,2-b] pyridazin-6-yl] thieno [3,2- b]pyridin-2-yl]piperidine-l-carboxylic acid tert-butyl ester

A solution of 4-[6-[2-methyl-8-(trifluoromethyl)imidazo[l,2-b]pyridazin-6-yl]thieno[3,2- b]pyridin-2-yl]-3,6-dihydro-2H-pyridine-l-carboxylic acid tert-butyl ester (135 mg, 0.262 mmol, 1.000 eq) in methanol (12 mL) and dichloromethane (12 mL) was degassed by three vacuum / argon cycles. Addition of palladium on activated charcoal (139 mg, 0.131 mmol, 0.500 eq). The reaction mixture was degassed by three vacuum -hydrogen cycles and stirred for 72 hours under an atmosphere of hydrogen. The reaction mixture was filtered over decalite. The filtrate was evaporated in vacuo. The crude material was purified by flash chromatography to give the title compound (73 mg, 54%) as an off-white solid with a purity of 100%. [M+H]⁺= 518.3 Step 3: 6-[2-methyl-8-(trifluoromethyl)imidazo[l,2-b]pyridazin-6-yl]-2-(4- piperidyl)thieno[3,2-b]pyridine

To a solution of 4-[6-[2-methyl-8-(trifluoromethyl)imidazo[l,2-b]pyridazin-6-yl]thieno[3,2- b]pyridin-2-yl]piperidine-l-carboxylic acid tert-butyl ester (73 mg, 0.141 mmol, 1.000 eq) in di chloromethane (2 mL) was added TFA (740 mg, 500 pL, 6.49 mmol, 46.015 eq) at room temperature. Stirring was continued for 2 hours. The volatiles were evaporated. The residue was dissolved in MeOH (1 ml) and neutralized with 1 M aqueous ISfeCCh solution (4 mL). The precipitate was collected by filtration after 1 hour, washed with three 3-mL portions of water and dried in vacuo to give the title compound (43 mg, 73%) as light brown solid. [M+H]⁺= 418.3

Example 3

2-(4-Azaspiro[2.5]octan-7-yl)-6-(8-methoxy-2-methyl-imidazo[l,2-b]pyridazin-6- yl)thieno [3,2-b] pyridine

Step 1: tert-Butyl 7-(((trifluoromethyl)sulfonyl)oxy)-4-azaspiro[2.5]oct-6-ene-4-carboxylate

To a solution of tert-butyl 7-oxo-4-azaspiro[2.5]octane-4-carboxylate (CAS No: 1892578-21-0) (2.0 g, 8.88 mmol, 1.0 eq) in THF was dropwise added 1 M LiHMDS (CAS No: 4039-32-1) (9.8 mL, 9.77 mmol, 1.1 eq) at -78 °C under nitrogen atmosphere, stirred for about 20 min. Next, N,N- bis(trifluoromethylsulfonyl)aniline (3.49 g, 9.77 mmol, 1.1 eq) was added, then stirred at 25 °C for 3 hours. Next, EtOAc was added to the mixture followed by the addition of H2O. The aqueous layer was extracted with EtOAc, the combined organic layers were dried (Na2SO4), filtered and concentrated, the residue was purified by flash column chromatography (eluting with 0~60 % EtOAc in hexane) to get tert-butyl 7-(trifluoromethylsulfonyloxy)-4-azaspiro[2.5]oct-6-ene-4- carboxylate (1.5 g, 4.2 mmol, 47.28% yield) as a yellow solid. 'H NMR (400 MHz, DMSO) 8 6.13 (s, 1H), 4.00 (s, 2H), 2.38 (s, 2H), 1.39 (d, J= 4.0 Hz, 9H), 0.82 (d, J= 47.4 Hz, 4H).

Step 2: tert-Butyl 7-(4,4,5,5-tetramethyl-l,3,2-dioxaborolan-2-yl)-4-azaspiro[2.5]oct-6-ene- 4-carboxylate

To a solution of tert-butyl 7-(trifluoromethylsulfonyloxy)-4-azaspiro[2.5]oct-6-ene-4-carboxylate (700.0 mg, 1.96 mmol, 1.0 eq), bis(pinacolato)diboron (547.18 mg, 2.15 mmol, 1.1 eq), KO Ac (383.94 mg, 3.92 mmol, 2.0 eq) and Pd(dppf)C12 (143.33 mg, 0.2 mmol, 0.1 eq) in 1,4-dioxane (10 mL) was stirred at 100 °C for 4 hours under nitrogen atmosphere, Then concentrated to dryness. The crude was purified by flash column chromatography (eluting with 0~60 %EtOAc in Hexane) to get tert-butyl 7-(4,4,5,5-tetramethyl-l,3,2-dioxaborolan-2-yl)-4-azaspiro[2.5]oct-6-ene-4- carboxylate (500.0 mg, 1.49 mmol, 76.14% yield) as brown solid. MS [M+H]+: 236.3

Step 3: tert-Butyl 7-(6-bromothieno[3,2-b]pyridin-2-yl)-4-azaspiro[2.5]oct-6-ene-4- carboxylate

To a solution of 6-bromo-2-iodo-thieno[3,2-b]pyridine (250.0 mg, 0.74 mmol, 1.0 eq), tert-butyl 7-(4,4,5,5-tetramethyl-l,3,2-dioxaborolan-2-yl)-4-azaspiro[2.5]oct-6-ene-4-carboxylate (246.52 mg, 0.74 mmol, 1.0 eq) and ISfeCCL (155.88 mg, 1.47 mmol, 2.0 eq) in Water (1 mL) / Toluene (5 mL) / Ethanol (5 mL) was added Pd(PPh3)4 (84.97 mg, 0.07 mmol, 0.1 eq), the mixture was stirred at 70 °C for 10 hours under nitrogen atmosphere. The mixture was cooled and dilute with water (200 mL), extracted with DCM (100 mL*2), the organics was washed with brine (100 mL), dried over anhydrous Na2SO4, filtered and concentrated, the residue was purified by silica gel column (eluting with 0-30% EtOAc in Hexane) to afford tert-butyl 7-(6-bromothieno[3,2-b]pyridin-2-yl)- 4-azaspiro[2.5]oct-6-ene-4-carboxylate (160.0 mg, 0.38 mmol, 51.64% yield) as light yellow solid. MS [M+H]+: 421.1

Step 4: tert-Butyl 7-(6-(8-methoxy-2-methylimidazo[l,2-b]pyridazin-6-yl)thieno[3,2- b]pyridin-2-yl)-4-azaspiro[2.5]oct-6-ene-4-carboxylate

A mixture of tert-butyl 7-(6-bromothieno[3,2-b]pyridin-2-yl)-4-azaspiro[2.5]oct-6-ene-4- carboxylate (140.0 mg, 0.33 mmol, 1.0 eq), 8-methoxy-2-methyl-6-(4,4,5,5-tetramethyl-l,3,2- dioxaborolan-2-yl)imidazo[l,2-b]pyridazine (192.14 mg, 0.66 mmol, 2.0 eq), Pd(dppf)C12 (36.47 mg, 0.05 mmol, 0.15 eq) and K2CO3 (137.76 mg, 1.0 mmol, 3.0 eq) in 1,4-dioxane (2.5 mL) and Water (0.5 mL) was stirred at 90 °C for 10 hours under nitrogen atmosphere. The mixture was diluted with EtOAc (80 mL) and then washed with 2 x50 ml water, 50 ml saturated brine. The organics were dried (MgSCh) before. The crude was purified by flash column chromatography (eluting with 0~5% MeOH in DCM) to afford tert-butyl 7-[6-(8-methoxy-2 -methyl -imidazof 1,2- b]pyridazin-6-yl)thieno[3,2-b]pyridin-2-yl]-4-azaspiro[2.5]oct-6-ene-4-carboxylate (120.0 mg, 0.24 mmol, 67.14% yield) as yellow solid. MS [M+H]⁺: 504.1

Step 5: tert-Butyl 7-(6-(8-methoxy-2-methylimidazo[l,2-b]pyridazin-6-yl)thieno[3,2- b]pyridin-2-yl)-4-azaspiro[2.5]octane-4-carboxylate

To a solution of tert-butyl 7-[6-(8-methoxy-2-methyl-imidazo[l,2-b]pyridazin-6-yl)thieno[3,2- b]pyridin-2-yl]-4-azaspiro[2.5]oct-6-ene-4-carboxylate (100.0 mg, 0.2 mmol, 1.0 eq) in EtOAc (20 mL) was added Pd/C (20 mg, 10%), the mixture was stirred at 50 °C for 24 hours under hydrogen atmosphere. The mixture was filtered through celite, then concentrated in vacuum to afford tertbutyl 7-[6-(8-methoxy-2-methyl-imidazo[l,2-b]pyridazin-6-yl)thieno[3,2-b]pyridin-2-yl]-4- azaspiro[2.5]octane-4-carboxylate (80.0 mg, 0.16 mmol, 79.68% yield) as a light yellow solid. MS [M]⁺: 506.2

Step 6: 6-(8-Methoxy-2-methylimidazo[l,2-b]pyridazin-6-yl)-2-(4-azaspiro[2.5]octan-7- yl)thieno[3,2-b]pyridine trifluoroacetic acid (alternative chemical name: 6-(8-methoxy-2- methylimidazo [1,2-b] pyridazin-6-yl)-2-(4-azaspiro [2.5] octan-7-yl)thieno [3,2-b] pyridine)

A solution of tert-butyl 7-[6-(8-methoxy-2-methyl-imidazo[l,2-b]pyridazin-6-yl)thieno[3,2- b]pyridin-2-yl]-4-azaspiro[2.5]octane-4-carboxylate (70.0 mg, 0.14 mmol, 1.0 eq) in HCl/dioxane(4M, 2 mL) was stirred at 25 °C for 1 hour. The mixture was concentrated and purified by prep-HPLC (column Gemini 5p C18 150 x 21.2 mm (ACN-H2O, 0.1% TFA)) to afford 2-(4- azaspiro[2.5]octan-7-yl)-6-(8-methoxy-2-methyl-imidazo[l,2-b]pyridazin-6-yl)thieno[3,2- b]pyridine;2,2,2-trifhioroacetic acid (22.1 mg, 0.04 mmol, 28.45% yield) as yellow solid. MS [M+H]⁺: 405.9 ¹ H NMR (400 MHz, D2O) S 9.09 (s, 2H), 7.94 (d, J = 0.9 Hz, 1H), 7.39 (d, J = 6.8 Hz, 2H), 4.14 (s, 3H), 3.58 - 3.45 (m, 2H), 3.33 - 3.19 (m, 1H), 2.43 (s, 3H), 2.36 (d, J = 12.5 Hz, 2H), 2.04 - 1.91 (m, 1H), 1.71 (d, J = 15.6 Hz, 1H), 1.08 - 1.00 (m, 2H), 0.92 - 0.82 (m, 2H).

Example 4

6-(2,8-Dimethylimidazo [1,2-b] pyridazin-6-yl)-2-(4-piperidyl)thieno [3,2-b] pyridine

Step 1 : 4- [6-(2,8-dimethylimidazo [1,2-b] pyridazin-6-yl)thieno [3,2-b] pyridin-2-yl]-3,6- dihydro-2H-pyridine-l-carboxylic acid tert-butyl ester

To a mixture of (2,8-dimethylimidazo[l,2-b]pyridazin-6-yl)boronic acid (547 mg, 2.86 mmol, 2.000 eq; prepared according to the procedures described in W02019/057740), 4-(6- chlorothieno[3,2-b]pyridin-2-yl)-3,6-dihydro-2H-pyri dine- 1 -carboxylic acid tert-butyl ester (503 mg, 1.43 mmol, 1.000 eq) and K2CO3 (793 mg, 5.74 mmol, 4.008 eq) in acetonitrile (6 mL) and water (0.7 mL) was added l,r-bis(diphenylphosphino)ferrocene-palladium(II)di chloride di chloromethane complex (119 mg, 0.143 mmol, 0.100 eq) at room temperature. The reaction mixture was heated in a sealed tube at 95 °C (heat-on plate of 95 °C) and stirred for 1.5 hours. The mixture was partitioned between ethyl acetate (50 ml) and IM Na2CCh sol (30 ml). The layers were separated. The aqueous layer was extracted with two 50-ml portions of ethyl acetate. The combined organic layers were washed with one 30-ml portion of brine and concentrated in vacuo. The crude material was purified by flash chromatography to give the title compound (147 mg, 22 %) as a light brown/orange solid with a purity of 95%. MS [M+H]⁺: 462.3

Step 2: 4-[6-(2,8-dimethylimidazo[l,2-b]pyridazin-6-yl)thieno[3,2-b]pyridin-2-yl]piperidine- 1-carboxylic acid tert-butyl ester A solution of 4-[6-(2,8-dimethylimidazo[l,2-b]pyridazin-6-yl)thieno[3,2-b]pyridin-2-yl]-3,6- dihydro-2H-pyridine-l -carboxylic acid tert-butyl ester (97 mg, 0.210 mmol, 1.000 eq) in methanol (9.7 mL) and di chloromethane (9.7 mL) was degassed by three vacuum / argon cycles. Addition of Palladium on activated charcoal (112 mg, 0.105 mmol, 0.500 eq). The reaction mixture was degassed by three vaccum-hydrogen cycles and stirred overnight under an atmosphere of hydrogen. The reaction mixture was filtered over decalite, redissolved in methanol (9.7 mL) and di chloromethane (9.7 mL) and the reaction re-started. The reaction mixture was filtered over decalite and the solvent evaporated in vacuo. The crude material was purified by flash chromatography to give the title compound (22 mg, 22%) as light brown solid. MS [M+H]⁺: 464.5

Step 3: 6-(2,8-dimethylimidazo[l,2-b]pyridazin-6-yl)-2-(4-piperidyl)thieno[3,2-b]pyridine

To a solution of 4-[6-(2,8-dimethylimidazo[l,2-b]pyridazin-6-yl)thieno[3,2-b]pyridin-2- yl]piperidine-l -carboxylic acid tert-butyl ester (22 mg, 0.047 mmol, 1.000 eq) in dichloromethane (2 mL) was added TFA (740 mg, 500 uL, 6.49 mmol, 136.764 eq) at room temperature. Stirring was continued for 2 hours. The volatiles were evaporated. The residue was dissolved in MeOH (1 mL) and neutralized with 1 M aq NazCO, solution (4 mL). The mixture was partitioned between ethyl acetate (30 ml) and IM Na2CCh sol (20 mL). The layers were separated. The aq layer was extracted with two 50-ml portions of ethyl acetate. The combined organic layers were washed with one 30-ml portion of brine dried over sodium sulfate, filtered and concentrated in vacuo. The residue was dissolved in ethyl acetate (3 ml). Addition of 4 M HC1 in 1,4-dioxane (119 uL, 0.475 mmol, 10.000 eq). The precipitate was collected by filtration, washed with three 2-ml portions of ethyl acetate and dried in vacuo to give the title compound (12 mg, 56%) as light brown solid (hydrochloric acid). MS [M+H]⁺: 364.3

Example 5

6-(2-Methylimidazo [1 ,2-b] pyridazin-6-yl)-2-(4-piperidyl)thieno [3,2-b] pyridine

Step 1: tert-Butyl 4-(6-(2-methylimidazo[l,2-b]pyridazin-6-yl)thieno[3,2-b]pyridin-2-yl)- 3,6-dihydropyridine-l(2H)-carboxylate

The mixture of tert-butyl 4-(6-bromothieno[3,2-b]pyridin-2-yl)-3,6-dihydro-2H-pyridine-l- carboxylate (200.0 mg, 0.5 mmol, 1.0 eq), (2-methylimidazo[l,2-b]pyridazin-6-yl)boronic acid (179.1 mg, 0.6 mmol, 1.2 eq), XPhos Pd G3 (CAS No: 1445085-55-1) (42.9 mg, 0.1 mmol, 0.1 eq) and triethylamine (153.6 mg, 1.5 mmol, 3.0 eq) in 1,4-dioxane (16 mL) and water (4 mL) was stirred at 110 °C for 6 hours under nitrogen atmosphere. The cooled mixture was concentrated and the residue was purified by combi-flash with 3% MeOH in DCM to afford tert-butyl 4-[6-(2- methylimidazo[l,2-b]pyridazin-6-yl)thieno[3,2-b]pyri din-2 -yl]-3,6-dihydro-2H-pyri dine-1- carboxylate (190.0 mg, 0.42 mmol, 81.39% yield) as a yellow solid. MS [M+H]⁺: 447.9.

'H NMR (400 MHz, DMSO) 8 9.26 (d, J= 2.0 Hz, 1H), 9.03 (d, J= 1.8 Hz, 1H), 8.15 (t, J = 4.6 Hz, 2H), 7.87 (d, J= 9.6 Hz, 1H), 7.60 (s, 1H), 6.45 (s, 1H), 4.09 (s, 2H), 3.58 (d, J= 5.2 Hz, 2H), 2.63 (s, 2H), 2.43 (s, 3H), 1.44 (s, 9H).

Step 2: tert-butyl 4-(6-(2-methylimidazo[l,2-b]pyridazin-6-yl)thieno[3,2-b]pyridin-2- yl)piperidine-l-carboxylate

To a solution of tert-butyl 4-[6-(2-methylimidazo[l,2-b]pyridazin-6-yl)thieno[3,2-b]pyridin-2-yl]- 3,6-dihydro-2H-pyridine-l-carboxylate (170.0 mg, 0.4 mmol, 1.0 eq) in ethyl acetate (30 mL) was added Pd/C (50 mg, 10%) at room temperature. The mixture was stirred at 50 °C under hydrogen atmosphere for 16 hours. The mixture was filtered, and the filtrate was concentrated to give tertbutyl 4-[6-(2-methylimidazo[ 1 ,2-b]pyridazin-6-yl)thieno[3 ,2-b]pyridin-2-yl]piperidine- 1 - carboxylate (130.0 mg, 0.29 mmol, 75.37% yield) as a light yellow solid. MS [M+H]⁺: 450.0

'H NMR (400 MHz, DMSO) 8 9.26 (d, J= 2.1 Hz, 1H), 9.04 (d, J= 1.5 Hz, 1H), 8.17 - 8.11 (m, 2H), 7.86 (d, J= 9.6 Hz, 1H), 7.46 (s, 1H), 4.06 (s, 2H), 3.20 (t, J= 11.2 Hz, 1H), 2.90 (s, 2H), 2.42 (s, 3H), 2.06 (d, J= 12.4 Hz, 2H), 1.68 - 1.51 (m, 2H), 1.42 (s, 9H).

Step 3: 6-(2-methylimidazo[l,2-b]pyridazin-6-yl)-2-(piperidin-4-yl)thieno[3,2-b]pyridine (alternative chemical name: 6-(2-methylimidazo[l,2-b]pyridazin-6-yl)-2-(piperidin-4- yl)thieno [3,2-b] pyridine) To a solution of tert-butyl 4-[6-(2-methylimidazo[l,2-b]pyridazin-6-yl)thieno[3,2-b]pyridin-2- yl]piperidine-l -carboxylate (130.0 mg, 0.3 mmol, 1.0 eq) in DCM (10 mL) was added trifluoroacetic acid (1.0 mL), the reaction was stirred at 25 °C for 1 hour. The solvent was concentrated and the residue was purified by Prep-HPLC (Gemini-C18 150 x 21.2 mm, 5pm, acetonitrile / water as eluent with 0.1%TFA as modifier) to afford 6-(2-methylimidazo[l,2- b]pyridazin-6-yl)-2-(4-piperidyl)thieno[3,2-b]pyridine;2,2,2-trifluoroacetic acid (117.0 mg, 0.25 mmol, 85.11% yield) as a yellow solid. MS [M]+: 349.9

'H NMR (400 MHz, DMSO) 5 9.31 (d, J= 2.1 Hz, 1H), 9.13 (d, J= 1.8 Hz, 1H), 8.67 (s, 1H), 8.49 - 8.30 (m, 3H), 8.12 (d, J= 9.6 Hz, 1H), 7.51 (s, 1H), 3.47 - 3.34 (m, 3H), 3.08 (q, J= 12.6 Hz, 2H), 2.49 (s, 3H), 2.25 (d, J= 12.7 Hz, 2H), 1.99 - 1.81 (m, 2H).

Example 6

6-(8-Fluoro-2-methyl-imidazo[l,2-a]pyridin-6-yl)-2-(4-piperidyl)thieno[3,2-b]pyridine

Step 1 tert-butyl 4-(6-(8-fluoro-2-methylimidazo[l,2-a]pyridin-6-yl)thieno[3,2-b]pyridin-2- yl)-3,6-dihydropyridine-l(2H)-carboxylate

A suspension of tert-butyl 4-(6-bromothieno[3,2-b]pyridin-2-yl)-3,6-dihydro-2H-pyridine-l- carboxylate (200.0 mg, 0.51 mmol, 1.0 eq), (8-fluoro-2-methyl-imidazo[l,2-a]pyridin-6- yl)boronic acid (245.34 mg, 1.26 mmol, 2.5 eq), triethylamine (153.3 mg, 1.52 mmol, 3.0 eq) and Xphos-Pd-Gs (85.63 mg, 0.1 mmol, 0.2 eq) in 1,4-dioxane (8 mL) and water (2 mL) was heated at 100 °C for 3 hours under nitrogen atmosphere. Then the solvent was concentrated in vacuo and the residue was purified by silica gel column chromatography (diluted with EtOAc/hexane=l :2) to afford tert-butyl 4-[6-(8-fluoro-2-methyl-imidazo[l,2-a]pyridin-6-yl)thieno[3,2-b]pyridin-2-yl]- 3,6-dihydro-2H-pyridine-l-carboxylate (180 mg, 0.38 mmol, 76.59% yield) as a light yellow solid. MS (ESI), m/z: [M+H]⁺= 465

Step 2: tert-butyl 4-(6-(8-fluoro-2-methylimidazo[l,2-a]pyridin-6-yl)thieno[3,2-b]pyridin-2- yl)piperidine-l-carboxylate

To a solution of tert-butyl 4-[6-(8-fluoro-2-methyl-imidazo[l,2-a]pyridin-6-yl)thieno[3,2- b]pyridin-2-yl]-3,6-dihydro-2H-pyridine-l-carboxylate (180.0 mg, 0.36 mmol, 1.0 eq) in EtOAc (20 mL) was added Pd/C (180.0 mg). The resulting mixture was charged into hydrogen and stirred for 18 hours at 50 °C under 1.0 atm. The solids were filtered out and the filtrate was applied onto a silica gel column with EtOAc/hexane=2: l to afford the tert-butyl 4-[6-(8-fluoro-2-methyl- imidazo[l,2-a] pyridin-6-yl)thieno[3,2-b]pyridin-2-yl]piperidine-l-carboxylate (130.0 mg, 0.28 mmol, 86.09% yield) as a yellow solid.

MS (ESI), m/z: calcd for C25H27FN4O2S, Molecular Weight: 466, found RT=1.17 min, [M+H]⁺= 467.

Step 3: 6-(8-fluoro-2-methyl-imidazo[l,2-a]pyridin-6-yl)-2-(4-piperidyl)thieno[3,2- bjpyridine (alternative chemical name: 6-(8-fluoro-2-methylimidazo[l,2-a]pyridin-6-yl)-2- (piperidin-4-yl)thieno [3,2-b] pyridine)

To a solution of tert-butyl 4-[6-(8-fluoro-2-methyl-imidazo[l,2-a]pyridin-6-yl)thieno[3,2-b] pyridine-2-yl]piperidine-l -carboxylate (130.0 mg, 0.32 mmol, 1.0 eq) in DCM (6 mL) was added TFA (2.0 mL), the mixture was stirred at 25 °C for 1 hour. The mixture was concentrated in vacuo and the residue was purified by prep-HPLC (column: Gemini 5p C18 150 x 21.2 mm, ACN- H2O(0.1%TFA)) to afford 6-(8-fluoro-2-methyl-imidazo[l,2-a]pyridin-6-yl)-2-(4-piperidyl) thie- no[3,2-b]pyridine;2,2,2-trifluoroacetic acid (55.4 mg, 0.12 mmol, 33.62% yield) as a light yellow oil.

MS (ESI), m/z: calcd for C20H19FN4S, Molecular Weight: 366, found RT=0.83 min, [M+H]⁺= 367.

'H NMR (400 MHz, DMSO) 8 9.19 (d, J = 1.2 Hz, 1H), 9.05 (d, J = 2.1 Hz, 1H), 8.86 (d, J = 1.8 Hz, 1H), 8.80 (d, J = 9.7 Hz, 1H), 8.54 (d, J = 9.9 Hz, 1H), 8.22 (d, J = 11.8 Hz, 1H), 8.09 (d, J = 1.4 Hz, 1H), 7.48 (s, 1H), 3.48 - 3.32 (m, 3H), 3.09 (q, J = 12.5 Hz, 2H), 2.50 (s, 3H), 2.25 (d, J = 13.3 Hz, 2H), 1.97 - 1.84 (m, 2H).

Examples 7

2-[(7R)-4-Azaspiro[2.5]octan-7-yl]-6-(8-methoxy-2-methyl-imidazo[l,2-b]pyridazin-6- yl)thieno [3,2-b] pyridine

And

Example 8

2-[(7S)-4-Azaspiro[2.5]octan-7-yl]-6-(8-methoxy-2-methyl-imidazo[l,2-b]pyridazin-6- yl)thieno [3,2-b] pyridine

Step 1: tert-Butyl (R)-7-(6-(8-methoxy-2-methylimidazo[l,2-b]pyridazin-6-yl)thieno[3,2- b]pyridin-2-yl)-4-azaspiro[2.5]octane-4-carboxylate and tert-butyl (S)-7-(6-(8-methoxy-2- methylimidazo[l,2-b]pyridazin-6-yl)thieno[3,2-b]pyridin-2-yl)-4-azaspiro[2.5]octane-4- carboxylate

Tert-butyl 7-[6-(8-methoxy-2-methyl-imidazo[l,2-b]pyridazin-6-yl)thieno[3,2-b]pyridin-2-yl]-4- azaspiro[2.5]octane-4-carboxylate (990 mg, 1.96 mmol was separated with SFC (Thar prep 80 (CHIRALPAK AS-H 250mm x 20 mm, 5pm (40%IPA(NH4OH 0.2%))) to afford the corresponding two enantiomers. First eluted enantiomer (presume Pl) is tert-butyl (R)-7-(6-(8-methoxy-2-methylimidazo[l,2- b]pyridazin-6-yl)thieno[3,2-b]pyridin-2-yl)-4-azaspiro[2.5]octane-4-carboxylate (310 mg, 0.61 mmol, 26.17% yield) with light yellow solid. MS [M]+: 405.9

[a]^{27 8}D= -8 (c: 0.3 g/100 mL, CHCh)

Second eluted enantiomer (presume P2) is tert-butyl (S)-7-(6-(8-methoxy-2-methylimidazo[l,2- b]pyridazin-6-yl)thieno[3,2-b]pyridin-2-yl)-4-azaspiro[2.5]octane-4-carboxylate (305 mg, 0.6 mmol, 20.6% yield) with also light yellow solid. MS [M]+: 405.9

[a]²⁸ +6.67 (c: 0.3 g/100 mL, CHCh)

Step 2a: 2- [(7R)-4-azaspiro [2.5] octan-7-yl]-6-(8-methoxy-2-methyl-imidazo [1,2-b] pyridazin- 6-yl)thieno [3, 2-b] pyridine (example 7, putative assignment of enantiomer)

To a solution of tert-butyl (7R)-7-[6-(8-methoxy-2-methyl-imidazo[l,2-b]pyridazin-6- yl)thieno[3,2-b]pyridin-2-yl]-4-azaspiro[2.5]octane-4-carboxylate (300.0 mg, 0.59 mmol, 1.0 eq) in DCM (5 mL) was added 4NHCl/dioxane (5.0 mL, 20.0 mmol, 33.71 eq), the mixture was stirred at 25 °C for 2 hours. Then the solvent was concentrated to dryness and the residue was triturated with DCM/ACN (6 mL, 5: 1) to get 2-[(7R)-4-azaspiro[2.5]octan-7-yl]-6-(8-methoxy-2-methyl- imidazo[l,2-b]pyridazin-6-yl)thieno[3,2-b]pyridine;hydrochloride (246.5 mg, 0.56 mmol, 91.93% yield) as a light yellow solid. MS [M]+: 406.1

[a]²⁶ D= -47.33 (c: 0.3 g/100 mL, MeOH)

'H NMR (400 MHz, DMSO) S 9.96 (s, 1H), 9.49 (d, J = 11.0 Hz, 1H), 9.41 (d, J = 2.0 Hz, 1H), 9.31 (d, J = 1.8 Hz, 1H), 8.47 (s, 1H), 7.98 (s, 1H), 7.54 (s, 1H), 4.32 (s, 3H), 3.57 - 3.36 (m, 2H), 3.11 (dd, J = 22.8, 11.6 Hz, 1H), 2.52 (d, J = 3.2 Hz, 3H), 2.44 (d, J = 12.7 Hz, 1H), 2.31 (d, J = 15.1 Hz, 1H), 2.07 (dd, J = 21.8, 12.6 Hz, 1H), 1.76 - 1.67 (m, 1H), 1.22 - 1.03 (m, 2H), 0.86 (s, 2H).

Step 2b: 2-[(7S)-4-azaspiro[2.5]octan-7-yl]-6-(8-methoxy-2-methyl-imidazo[l,2-b]pyridazin- 6-yl)thieno [3, 2-b] pyridine (example 8, putative assignment of enantiomer)

To a solution of tert-butyl (7S)-7-[6-(8-methoxy-2-methyl-imidazo[l,2-b]pyridazin-6- yl)thieno[3,2-b]pyridin-2-yl]-4-azaspiro[2.5]octane-4-carboxylate (260.0 mg, 0.51 mmol, 1.0 eq) in DCM (5 mL) was added 4N HCl/dioxane (5.0 mL, 20.0 mmol, 38.89 eq), the mixture was stirred at 25 °C for 2 hours. Then the solvent was evaporated to dryness and the residue was purified by prep-HPLC (Gemini-C18 150 x 21.2 mm, 5pm, ACN-H2O(0.1%FA) 10-15%), the desired fraction was lyophilized to get 2-[(7S)-4-azaspiro[2.5]octan-7-yl]-6-(8-methoxy-2-methyl- imidazo[l,2-b]pyridazin-6-yl)thieno[3,2-b]pyridine;formic acid (119.4 mg, 0.26 mmol, 50.97% yield) as a white solid. MS [M]+: 406.1

[a]^{26 3}D= +48 (c: 0.3 g/100 mL, MeOH)

'H NMR (400 MHz, DMSO) S 9.29 (s, 1H), 9.07 (s, 1H), 8.14 (s, 0.5H), 8.03 (s, 1H), 7.46 (s, 1H), 7.31 (s, 1H), 4.16 (s, 3H), 3.41 (s, 2H), 3.01 (s, 1H), 2.37 (s,

3H), 2.30 - 2.18 (m, 2H), 1.82 (d, J = 10.4 Hz, 1H), 1.63 (d, J = 11.4 Hz, 1H), 0.80 (dd, J = 32.5, 21.4 Hz, 4H).

Example 9

2-(4- Azaspiro [2.5] octan-7-yl)-6- [8-(difluoromethoxy)-2-methyl-imidazo [1,2-b] pyridazin-6- yljthieno [3,2-b] pyridine

Step 1: tert-butyl 7-[6-[8-(difluoromethoxy)-2-methyl-imidazo[l,2-b]pyridazin-6- yl]thieno[3,2-b]pyridin-2-yl]-4-azaspiro[2.5]oct-6-ene-4-carboxylate

The solution of tert-butyl 7-(6-bromothieno[3,2-b]pyridin-2-yl)-4-azaspiro[2.5]oct-6-ene-4- carboxylate (500.0 mg, 1.19 mmol, 1.0 eq), [8-(difhioromethoxy)-2-m ethyl -imidazof 1,2- b]pyridazin-6-yl]boronic acid (288.34 mg, 1.19 mmol, 1.0 eq), [1,1'- bis(diphenylphosphino)ferrocene]dichloropalladium(II) (86.83 mg, 0.12 mmol, 0.1 eq) and potassium carbonate (492.01 mg, 3.56 mmol, 3.0 eq) in 1,4-dioxane (8 mL) and water (2 mL) was heated at 90 °C for 10 hours under nitrogen atmosphere. The solvent was evaporated and the residue was purificed by silica gel column chromatography (eluting 0~5% MeOH in DCM) to afford the title compound (260.0 mg, 0.48 mmol, 40.6% yield) as a yellow solid. M+H [540.3]+, RT=1.51

Step 2: tert-butyl 7-[6-[8-(difluoromethoxy)-2-methyl-imidazo[l,2-b]pyridazin-6- yl]thieno[3,2-b]pyridin-2-yl]-4-azaspiro[2.5]octane-4-carboxylate

To a solution of tert-butyl 7-[6-[8-(difluoromethoxy)-2-methyl-imidazo[l,2-b]pyridazin-6- yl]thieno[3,2-b]pyridin-2-yl]-4-azaspiro[2.5]oct-6-ene-4-carboxylate (230.0 mg, 0.43 mmol, 1.0 eq) in ethyl acetate (150 mL) was added Pd/C (20.0 mg). The resulting mixture was charged into hydrogen and stirred for 48 hours at 50 °C under 1.0 atm. The mixture was filtered, the filtrate was concentrated in vacuum to afford the title compound (220.0 mg, 0.41 mmol, 89.58% yield) as light yellow solid. M+H [542.2]+, RT=1.54

Step 3: 2-(4-azaspiro[2.5]octan-7-yl)-6-[8-(difluoromethoxy)-2-methyl-imidazo[l,2- b] pyr idazin-6-yl] thieno [3,2-b] pyridine

To a solution of tert-butyl 7-[6-[8-(difluoromethoxy)-2-methyl-imidazo[l,2-b]pyridazin-6- yl]thieno[3,2-b]pyridin-2-yl]-4-azaspiro[2.5]octane-4-carboxylate (200.0 mg, 0.37 mmol, 1.0 eq) in dichloromethane (5 mL) was added HC1 in dioxane (3.0 mL, 12.0 mmol, 14.39 eq), the mixture was stirred at 25 °C for 2 hours. The solids were filtered to afford 2-(4-azaspiro[2.5]octan-7-yl)-6- [8-(difluoromethoxy)-2-methyl-imidazo[l,2-b]pyridazin-6-yl]thieno[3,2- b]pyridine;hydrochloride (174.46 mg, 0.37 mmol, 92.08% yield) as light yellow solid. M+H [442.2]+, RT=1.00.

'H NMR (400 MHz, DMSO) 8 10.13 (s, 1H), 9.72 (d, J = 8.8 Hz, 1H), 9.42 (s, 2H), 8.41 (s, 1H), 8.10 (t, J = 35.7 Hz, 2H), 7.58 (s, 1H), 3.55 (t, J = 11.7 Hz, 1H), 3.38 (d, J = 12.2 Hz, 1H), 3.15 - 3.05 (m, 1H), 2.51 - 2.45 (m, 4H), 2.30 (d, J = 13.1 Hz, 1H), 2.12 (d, J = 12.0 Hz, 1H), 1.69 (d, J = 13.2 Hz, 1H), 1.16 (s, 2H), 0.86 (s, 2H).

Example 10

2-[(7R)-4-Azaspiro[2.5]octan-7-yl]-6-[8-(difluoromethoxy)-2-methyl-imidazo[l,2- b] pyridazin-6-yl] thieno [3,2-b] pyridine

And

Example 11

2- [(7S)-4- Azaspiro [2.5] octan-7-yl]-6- [8-(difluoromethoxy)-2-methyl-imidazo [1,2- b] pyridazin-6-yl] thieno [3,2-b] pyridine

Step 1: (7R)-7-[6-[8-(Difluoromethoxy)-2-methyl-imidazo[l,2-b]pyridazin-6-yl]thieno[3,2- b]pyridin-2-yl]-4-azaspiro[2.5]octane-4-carboxylic acid tert-butyl ester and (7S)-7-[6-[8- (difluoromethoxy)-2-methyl-imidazo [1,2-b] pyridazin-6-yl]thieno [3,2-b] pyridin-2-yl]-4- azaspiro[2.5]octane-4-carboxylic acid tert-butyl ester tert-butyl 7-[6-[8-(difluoromethoxy)-2-methyl-imidazo[l,2-b]pyridazin-6-yl]thieno[3,2- b]pyridin-2-yl]-4-azaspiro[2.5]octane-4-carboxylate (150 mg, 0.314 mmol was separated with SFC (chiral OZ, 5um, 250x20 mm; CCb/MeOH + 0.2% diethylamine) to afford the corresponding two enantiomers.

Presume Pl is (7R)-7-[6-[8-(difluoromethoxy)-2-methyl-imidazo[l,2-b]pyridazin-6-yl]thieno[3,2- b]pyridin-2-yl]-4-azaspiro[2.5]octane-4-carboxylic acid tert-butyl ester (16 mg, 26.17% yield) as withe solid solid. MS [M]+: 586.6

[a]^{27 8} _D= -0.28 (c: 1.0 g/100 mL, MeOH) Presume P2 is (7S)-7-[6-[8-(difluoromethoxy)-2-methyl-imidazo[l,2-b]pyridazin-6-yl]thieno[3,2- b]pyridin-2-yl]-4-azaspiro[2.5]octane-4-carboxylic acid tert-butyl ester (19 mg, 11.2% yield) as white solid. MS [M]+: 586.6

[a]²⁸ +0.24 (c: 1.0 g/100 mL, MeOH)

Step 2a: 2-[(7R)-4-azaspiro[2.5]octan-7-yl]-6-[8-(difluoromethoxy)-2-methyl-imidazo[l,2- b] pyr idazin-6-yl] thieno [3,2-b] pyridine

To a solution of (7R)-7-[6-[8-(difluoromethoxy)-2-methyl-imidazo[l,2-b]pyridazin-6- yl]thieno[3,2-b]pyridin-2-yl]-4-azaspiro[2.5]octane-4-carboxylic acid tert-butyl ester (16 mg, 0.030 mmol, 1.00 eq) in propanol (2 mL) was added aqueous HC1 cone. 37% (240 mg, 200 uL, 2.44 mmol, 82.45 eq). The reaction mixture was heated at 70 °C for 1 hour. The solvents were evaporated to afford 2-[(7R)-4-azaspiro[2.5]octan-7-yl]-6-[8-(difluoromethoxy)-2-methyl- imidazo[l,2-b]pyridazin-6-yl]thieno[3,2-b]pyridine;hydrochloride. MS [M]+: 442.2

[a]^{20 0} _D= -1.99 (c: 1.0 g/100 mL, MeOH)

Step 2b: 2-[(7S)-4-azaspiro[2.5]octan-7-yl]-6-[8-(difluoromethoxy)-2-methyl-imidazo[l,2- b] pyridazin-6-yl]thieno [3,2-b] pyridine

To a solution of (7S)-7-[6-[8-(difluoromethoxy)-2-methyl-imidazo[l,2-b]pyridazin-6- yl]thieno[3,2-b]pyridin-2-yl]-4-azaspiro[2.5]octane-4-carboxylic acid tert-butyl ester (19 mg, 0.035 mmol, 1.000 eq.) in propanol (2 mL) was added aqueous HC1 cone. 37% (240 mg, 200 uL, 2.44 mmol, 82.445 eq). The reaction mixture was heated at 70 °C for 1 hour. The solvents were evaporated to afford 2-[(7S)-4-azaspiro[2.5]octan-7-yl]-6-[8-(difluoromethoxy)-2-methyl- imidazo[l,2-b]pyridazin-6-yl]thieno[3,2-b]pyridine;hydrochloride. MS [M]+: 442.2

[a]^{20 2} _D= +2.83 (c: 1.0 g/100 mL, MeOH)

Example 12

2-(4- Azaspiro [2.5] octan-7-yl)-6- [2-methyl-8-(trifluoromethoxy)imidazo [1,2-b] pyridazin-6- yljthieno [3,2-b] pyridine

Step 1 : tert-Butyl 7-[6-[2-methyl-8-(trifluoromethoxy)imidazo[l,2-b]pyridazin-6-yl]thieno[3,2- b]pyridin-2-yl]-4-azaspiro[2.5]oct-6-ene-4-carboxylate

A mixture of tert-butyl tert-butyl 7-(6-bromothieno[3,2-b]pyridin-2-yl)-4-azaspiro[2.5]oct-6-ene- 4-carboxylate (337.08 mg, 0.8 mmol, 1.0 eq), [2-methyl-8-(trifluoromethoxy)imidazo[l,2- b]pyridazin-6-yl]boronic acid (208.78 mg, 0.8 mmol, 1.0 eq), XPhos-Pd g3 (67.72 mg, 0.08 mmol, 0.1 eq) and potassium carbonate (331.69 mg, 2.4 mmol, 3.0 eq) in 1,4-dioxane (8 mL) and water (2 mL) was heated at 90 °C under nitrogen atmosphere for 10 h. The organic layer was concentrated in vacuo and the residue was purified by silica gel column chromatography (eluting 0-60% EtOAc in PE) to afford the title compound (30.0 mg, 0.05 mmol, 16.92% yield) as off-white solid.

M+H [557.8]+, RT=1.56

Step 2: tert-Butyl 7-[6-[2-methyl-8-(trifhioromethoxy)imidazo[L2-b]pyridazin-6-yl]thieno[3,2- b]pyridin-2-yl]-4-azaspiro[2.5]octane-4-carboxylate

To a solution of tert-butyl 7-[6-[2-methyl-8-(trifluoromethoxy)imidazo[l,2-b]pyridazin-6- yl]thieno[3,2-b]pyridin-2-yl]-4-azaspiro[2.5]oct-6-ene-4-carboxylate (30.0 mg, 0.05 mmol, 1.0 eq) in ethyl acetate (100 mL) was added Pd/C (20.0 mg, 10%). The resulting mixture was charged into hydrogen and stirred at 50 °C under 1.0 atm pressure for 24 hours. The solids were filtered off and the filtrate was concentrated under vacuum to get the title compound (28.0 mg, 0.05 mmol, 79.98% yield) as a white solid.

M+H [560.3]+, RT=1.54

Step 3 : 2-(4-Azaspiro[2.5]octan-7-yl)-6-[2-methyl-8-(trifluoromethoxy)imidazo[l,2-b]pyridazin- 6-yl]thieno[3,2-b]pyridine To a solution of tert-butyl 7-[6-[2-methyl-8-(trifluoromethoxy)imidazo[l,2-b]pyridazin-6- yl]thieno[3,2-b]pyridin-2-yl]-4-azaspiro[2.5]octane-4-carboxylate (23.0 mg, 0.04 mmol, 1.0 eq) in DCM (3 mL) was added 4N hydrogen chloride solution in 1, 4-di oxane (3.0 mL, 12.0 mmol, 291.97 eq), the mixture was stirred at 25 °C for 2 hours. The solvent was evaporated and the residue was purified by prep-HPLC (Gemini -C18 150 x 21.2 mm, 5um ACN-H2O (0.1%TFA)) to get the title compound (7.88 mg, 0.01 mmol, 32.49% yield) as a white solid.

M+H [460.2]+, RT=1.05

^XH NMR (400 MHz, DMSO) 8 9.29 (s, 1H), 9.12 (s, 1H), 8.32 (s, 1H), 7.93 (s, 1H), 7.51 (s, 1H), 3.49 (s, 3H), 2.46 (s, 3H), 2.35 (d,J = 13.8Hz, 2H), 1.84 (dd, J = 72.3, 14.0Hz, 2H), 1.07 - 0.86 (m, 4H).

Homogeneous Time Resolved Fluorescence for HTT lowering

The HTRF assay was adapted from Weiss et al. (Analytical Biochemistry Volume 395, Issue 1, 1 December 2009, Pages 8-15 and Analytical Biochemistry Volume 410, 2011, Pages 304-306) to cells from GENEAe020-A cell line (https://hpscreg.eu/cell-line/GENEAe020-A).

Compounds were tested for the effect of mutant HTT levels in Huntington patient human cells (GENEAe020-A cell line) using Homogeneous Time Resolved Fluorescence (HTRF) directed towards mutant HTT protein (mHTT). The GENEAe020-A cell line was derived by Genea Biocells from human blastocysts of HD donors. After assessing viability, cells were plated into 384 well collagen coated plates in growth media. Once cells adhered, media was removed and test compounds dissolved in DMSO were diluted with buffer solution and added to the adherent cells. Controls included experiments with no cells, DMSO with no compound, and Hsp90 inhibitor control. Cells were incubated with compounds and controls for 48 hours. Then, the cells were lysed and transferred to an assay plate containing HTRF labeled monoclonal antibodies developed by Paul Patterson (Ko et al., Brain Research Bulletin, Volume 56, Numbers 3 and 4, 2001, Pages 319-329) which recognize specific areas of the HTT protein. The terbium labeled “donor” antibody (2B7) binds to the N-terminus of the HTT protein and the Alexa488 labeled “acceptor” antibody (MW1) is specific for the polyglutamine region of the protein. Binding of the acceptor labeled antibody is more efficient for the extended polyglutamine repeats of mutant HTT protein which translates into a signal boost which enables the specific measurement of mutant HTT protein level. The HTRF donor and acceptor detection reagents were incubated with the cell lysate and the ratio between the signals of the two fluorophores is indicative of the relative quantities of mHTT.

The results of this assay are provided in Table 9 below. Table 9 provides the ECso (half maximal effective concentration) values for the reduction of mHTT obtained for particular examples of the present invention as measured by HTRF assay (data shown below is mean from three replicates).

Quantification of HTT and FOXM1 splice variants in Hs68 fibroblast cells by QPCR

Hs68 fibroblast cells obtained from European Collection of Authenticated Cell Culture (Cell line 89051701) were seeded at a density of 60’000 cells/cm² (100 pl cell suspension/well) in a 96 well plate in DMEM + 4.5 g Glucose (Gibco #31966) supplemented with 10% FBS (Thermo Fisher Scientific #A3160501), and placed in an incubator at 37°C with 10% CO2 and 85% humidity.

Cells were treated directly after seeding. Compounds were prepared in serial dilutions starting with final highest concentration of IpM with a 1 :3 dilution to obtain a l l point concentration series. Control wells were treated with 0.1% DMSO. A volume of 100 pl of the diluted compounds were added to the cell culture plate. After a treatment period of 24 hours, the experiment was terminated by washing the cells with cold PBS and then adding 50 pL of lysis solution (Cells-to-CT™ Bulk Lysis Reagents, Thermo Fisher Scientific # 4391851C) with 5min incubation. The reaction was stopped with 5 pl of the stop solution provided in the kit.

RT-qPCR reactions were processed on a Roche LightCycler LC480 Real-Time PCR System using 2 pl of the cell lysate in a 10 pl mixture containing 5 pl of the Ag-Path-ID One-Step RT-PCR (Applied Biosystems, AMI 005) buffer and 0.4 pl of the AmpliTaq Gold DNA Polymerase supplied in the kit, 0.1 pM of each forward and reverse primers listed in Table 8 and 0.04 pM of the probe (conjugated with FAM for the target and HEX for the housekeeping gene). The temperature cycle consisted of incubation at 48 °C for 15 minutes for the reverse transcription step, followed by reverse transcriptase inactivation at 95 °C during 10 minutes, 45 cycles of amplification (95°C for 15 seconds, 60 °C for 1 minute) and a cooling step at 4 °C during 15 seconds.

The primer and probe sequences in Table 8 were used for the measurement of splice isoforms using Taqman assays. EIF4G1 was used as the housekeeping gene for all QPCR assays. The Taqman PCR data was acquired using a Light Cycler 480 (Roche Diagnostics) and Cp Values in txt-file for the two channels 465-510 [FAM] and 533-580 [HEX] were used for the analysis.

The Cp value for the biological and technical replicates of the test gene (Cpl) housekeeping gene (Cp2) were calculated by automatic thresholding in the light cycler software (Lightcycler 480 Software release 1.5.1.62 SP3). The relative transcript level was calculated as follows

Cpl - Cycle threshold of test gene

Cp2 - Cycle threshold of the housekeeping gene

ACp = Cp2-Cpl

AACp = ACp(treatment condition)- ACp(control)

Relative transcript level = 2(-AACp)

The concentration response curve was generated using the concentration of the test item as (X) and the relative transcript level as the response (Y). The Curve was fitted using a four parameter logistic equation in XLfit or GraphPad Prism as follows y = (A+(B-A)/(l+(C/x)^AD))

A and B are the bottom and top plateaus of the curve, C the EC50 (or IC50), and D the slope factor (Hill slope).

The results of this assay are provided in Table 9 below. EC50 is the concentration of the test item causing half the maximum response. Hill Slope describes the steepness of the curve. Top is the maximum response and Bottom is the minimum response on the Y axis. For HTT Exon 50 - NF, the top was set to 1 and the bottom to 0. For HTT Exon 50 LF and FOXMlex9i, the bottom was set to 0 and the top was constrained to the maximum observed value for that experiment. Table 8 - Primers used for measurement of splice isoforms:

Table 9 - Exemplary HTT reduction and FOXM1 e9i increase on protein and/or RNA level:

Claims

1. A compound of formula (I)

wherein

R³ is hydrogen, halogen, alkyl, alkoxy, haloalkyl or haloalkoxy;

R⁴ is hydrogen, alkyl or halogen; and

A¹ is -N- or -CH-; or a pharmaceutically acceptable salt thereof.

2. A compound according to claim 1, wherein R¹ and R² are both hydrogen; or R¹ and R² together with the carbon atom which they are attached to, form cycloalkyl.

3. A compound according to claim 1 or 2, wherein R¹ and R² are both hydrogen; or R¹ and R² together with the carbon atom which they are attached to, form cyclopropyl.

4. A compound according to any one of claims 1 to 3, wherein R³ is hydrogen, methyl, methoxy, fluoro, trifluoromethyl, difluoromethoxy or trifluoromethoxy.

5. A compound according to any one of claims 1 to 4, wherein R⁴ is alkyl.

6. A compound according to any one of claims 1 to 5, wherein R⁴ is methyl.

7. A compound according to any one of claims 1 to 6, wherein Ai is -N-.

8. A compound according to any one of claims 1 to 6, wherein Ai is -CH-.

9. A compound of formula (I) according to any one of claims 1 to 8 selected from 6-(8-methoxy-2-methyl-imidazo[l,2-b]pyridazin-6-yl)-2-(4-piperidyl)thieno[3,2- b]pyridine;

6-(2-methylimidazo[l,2-b]pyridazin-6-yl)-2-(4-piperidyl)thieno[3,2-b]pyridine;

2-[(7S)-4-azaspiro[2.5]octan-7-yl]-6-(8-methoxy-2-methyl-imidazo[l,2-b]pyridazin-6- yl)thieno[3,2-b]pyridine;

10. A process for the preparation of a compound according to any one of claims 1 to 9, comprising at least one of the following steps: (b) the reaction of a compound of formula (Bl)

with a compound of formula (B2)

wherein in the above process, PF is a protecting group, Al, Rl, R2 and R3 are according to any one of the preceding claims

11. A compound according to any one of claims 1 to 9, when manufactured according to a process of claim 10.

12. A compound according to any one of claims 1 to 9 for use as therapeutically active substance.

13. A pharmaceutical composition comprising a compound according to any one of claims 1 to 9 and a therapeutically inert carrier.

14. A compound according to any one of claims 1 to 9 for use in the treatment or prophylaxis of a neurodegenerative disease, in particular Huntington’s disease.

15. The use of a compound according to any one of claims 1 to 9 for the treatment or prophylaxis of a neurodegenerative disease, in particular Huntington’s disease.

16. The use of a compound according to any one of claims 1 to 9 for the preparation of a medicament for the treatment or prophylaxis of a neurodegenerative disease, in particular Huntington’s disease.

17. A method for the treatment or prophylaxis of a neurodegenerative disease, in particular Huntington’s disease, which method comprises administering an effective amount of a compound according to any one of claims 1 to 9 to a patient in need thereof.

18. The invention as hereinbefore described.