HK1166632B - Method and substances for preparation of n-substituted pyridinium compounds - Google Patents

Description

Process and materials for preparing N-substituted pyridinium compounds

Background

The present invention relates to a process for the synthesis of N-substituted carboxylated pyridinium compounds by reacting a pentamethinium precursor with a primary amine. In this reaction, a heterocyclic ring of N-substituted carboxylated pyridinium is formed.

Pyridinium compounds are of particular interest, for example, in drug design, or as common organic synthetic intermediates, especially in natural product synthesis (Cheng, W. -C. and Kurth, M.J., organic preparations and products International 34(2002) 585-. The substituted pyridinium compound has important application in synthesizing NAD and carba-NAD respectively.

The standard synthetic route to substituted pyridinium compounds is by alkylating pyridine derivatives. However, this reaction is only applicable to the case of using halogenated primary alkanes. When halogenated secondary or tertiary alkanes are used, elimination occurs as an undesirable side reaction and yields are generally low. In addition, when the alkylation is carried out with an alkyl halide having a halogen atom attached to an asymmetric carbon atom, racemization occurs during the nucleophilic substitution reaction.

All these limitations are overcome using the "Zincke reaction", which is based on the reaction of Zincke salts with alkyl or aromatic amines. Zincke salts are activated pyridinium salts capable of reacting with primary amines (R-NH)₂) A reaction wherein the nitrogen at the 2 or 6 position, respectively, is induced to open a ring, which is in turn followed by a ring closure to form an R-substituted pyridinium compound. The Zincke reaction can also be accomplished with hydrazine, hydroxylamine and carboxylic acid hydrazides. Such Zincke reactions are used in solution and solid phase organic synthesis (Eda, m.et al, j.org.chem.65(2000) 5131-.

The main route in the art for preparing the desired Zincke salts is to react pyridine derivatives with 2, 4 dinitrohalobenzenes, preferably 2, 4 dinitrochlorobenzene and 2, 4 dinitrobromobenzene.

As is evident from the above description of the state of the art processes, the activators currently used are toxic, explosive or otherwise dangerous and therefore limit the scope of research applications. There have been discrete attempts to perform Zincke reactions under environmentally friendly conditions, for example, microwave assisted synthesis. However, such attempts still rely on explosive dinitrophenyl compounds and do not scale up the reaction without expensive precautions (Vianna, G.H.R. et al, Letter in Organic Chemistry 5(2008) 396-398).

Therefore, there is a need to improve the synthesis of N-substituted pyridinium compounds, for example, by avoiding dangerous activating reagents. The new less hazardous method should allow for safer manufacturing procedures, and be simpler, less hazardous, and more efficient at manufacturing the compounds on a larger scale.

Many 2-alkylaminopentadieneimine derivatives and NH4OAc or primary amines (R-NH) are known₂) Reacting under acidic condition to respectively obtain corresponding 3-alkylated pyridine and 1-R-3-alkyl substituted pyridinium compounds. The requisite 2-alkylaminopentadiene imine compounds may be obtained from N-tert-butylimino derivatives of aldehydes, deprotonated by LDA, and longChunmidinium (vinamidinium) reaction (Wypych, J.C. et al, J.org.chem.73(2008) 1169-.

However, the application of this method has unfortunate limitations. The absence of reactive groups, such as ester functions, enables the introduction of the 2 position of the aminopentadienimine system, which is indispensable, for example, for the synthesis of nicotinate derivatives.

A complete new approach is provided by the present invention.

We have surprisingly found that, for example, the pentamethinium salt 5-dimethylamino-4-methoxycarbonyl-penta-2, 4-dimethyl-dienylidene-ammonium tetrafluoroborate and a different primary amine (R-NH)₂) One-step cyclization is carried out to obtain the corresponding 1-R-substituted methyl nicotinate. Using this method, it is possible to obtain, for example, nicotinamide "carba nucleoside, ((3-carbamoyl-1- ((1R, 2S,3R,4R) -2, 3-dihydroxy-4-hydroxymethyl-cyclopentyl) -pyridinium; chloride salt), a precursor in the synthesis of carba analogs of NAD.

In one process of the invention, an aminopentadienylium compound is first provided. The compound is subsequently reacted with a primary amine (R6-NH)₂) The reaction affords the corresponding 1-R6-substituted pyridinium compound. The methods disclosed herein avoid the hazardous active agents described above. In addition, the formation of N-substituted pyridinium derivatives is also nearly quantifiable and can be easily scaled up.

Based on all these findings, many problems known in the art can be avoided and overcome.

Summary of The Invention

The invention relates to a method for synthesizing N-substituted pyridinium-3 carboxylate, which comprises the following steps: a) providing a pentamethinium salt, b) reacting the pentamethinium salt of step a) with a primary amine, and c) thereby obtaining an N-substituted pyridinium-3 carboxylate.

Detailed Description

A first embodiment of the present invention is directed to a method of synthesizing an N-substituted pyridinium-3 carboxylate comprising the steps of: a) providing a pentamethinium salt, b) reacting the pentamethinium salt of step (a) with a primary amine, and c) thereby obtaining an N-substituted pyridinium-3 carboxylate.

A preferred embodiment of the present invention relates to a method for synthesizing an N-substituted pyridinium carboxylate compound, comprising the steps of: (a) a pentamethinium salt is provided, as shown in formula I

Wherein X^-Is a counter-ion to the ion of the compound,

r1 is an alkoxy group selected from the group consisting of O-methyl, O-ethyl, O-propyl, and O-isobutyl, and R2 through R5 are independently methyl or ethyl.

b) Reacting the pentamethine onium salt of step (a) with a primary amine of formula II,

wherein R6 is a linear, branched, or cyclic, optionally substituted alkyl group,

c) to give an N-substituted pyridinium compound of the formula III

Wherein X^-R1, and R6 are as described above.

Suitable and preferred counterions are dodecyl sulfate, chlorine, PF6^-，BF4^-And ClO4^-. Preferred counterions are dodecyl sulfate, tetrafluorophosphate or tetrafluoroborate.

As noted above, R6 is preferably a linear, branched or cyclic, optionally substituted alkyl group. In preferred embodiments the alkyl group is a linear C1-C6 alkyl group, or a branched C3-C6 alkyl group, or a cyclic C5-C6 alkyl group, or the substituted alkyl group is a substituted linear C1-C6 alkyl group, or a substituted branched C3-C6 alkyl group, or a substituted cyclic C5-C6 alkyl group. Preferably R6 is a furanosyl or cyclopentyl residue. Preferred compounds of the formula II are linear or branched alkylamines or are furanosylamines or cyclopentylamines.

Surprisingly, the synthesis of the present invention has a high yield of the desired product if the synthesis is carried out under reaction conditions in which both a primary amine and a protonated form of the primary amine are present. In a preferred embodiment, the present invention relates to a process for the synthesis of N-substituted pyridinium-3-carboxylates comprising the steps of: (a) providing a pentamethinium salt, (b) reacting the pentamethinium salt of step (a) with a primary amine in the presence of a primary amine protonated form, and (c) thereby obtaining an N-substituted pyridinium-3 carboxylate.

Preferred processes of the invention are carried out under reaction conditions in which the ratio of primary amine to its corresponding protonated amine is from 2:1 to 1: 50. More preferably, the process of the invention has a ratio of primary amine to its corresponding protonated amine of from 1:1 to 1: 20. It may also be preferred that the ratio of primary amine to its corresponding protonated amine is from 1:2 to 1: 15.

The process of the present invention is suitable for the preparation of alkoxycarbonylpyridinium compounds. A preferred embodiment of the present invention relates to the use of pentamethine onium salts, wherein R1 is OCH3, in the process of the present invention, for example, to prepare N-substituted methoxycarbonylpyridinium compounds.

A more preferred embodiment of the present invention relates to the use of pentamethine ylides in the process according to the invention, wherein R2 to R5 are all methyl groups.

The study given in the examples section is focused on the conversion of the pentamethinium salt 5-dimethylamino-4-methoxycarbonyl-penta-2, 4-dimethyl-dienylidene-ammonium tetrafluoroborate with aminocarba ribose ((1R, 2S,3R,4R) -2, 3-dihydroxy-4-hydroxymethyl) -1-aminocyclopentane). The amino carba ribose was found to react almost quantitatively with the pentamethinium salt, for example, in the presence of pyridinium tetrafluoroborate as counter ion, to give the N-substituted nicotinate derivative. Surprisingly, the ester function is not affected by the primary amine.

The side reactions, such as the formation of dimethylamide, are due to the attack of the liberated dimethylamine on the ester function of the methyl nicotinate formed, which can be almost completely eliminated by using a suitable mixture of aminocarba ribose and its corresponding hydrochloride. It is convenient to add the pentamethine onium salt slowly and continuously, mixed with an equimolar amount of methanesulfonic acid.

The process of the invention can be extended to other primary amines. As the skilled artisan will appreciate that such primary amines may contain further substituents that do not interfere with the cyclization reaction. In a preferred embodiment the compound R6-NH2 is a substituted primary alkylamine.

Preferred substituted primary alkylamines for use in the methods of the invention are pure stereoisomers of amino alcohols and amino acids.

Preferred amino alcohols are derived from any naturally occurring and any commercially available unnatural amino acid. Preferred aminoalcohols are selected from the group consisting of serinol, threoninol, phenylalaninol, 2, 5-diamino-1-pentanol (from ornithine) and 2, 6-diamino-1-hexanol (from lysine).

If the compound of formula II is an amino acid, the amino acid may be selected from any naturally occurring and any non-natural amino acid. In preferred embodiments the amino acid is a naturally occurring amino acid or a non-naturally occurring, preferably commercially available, amino acid. Preferred compounds of formula II are amino acids selected from serine, threonine, phenylalanine, ornithine, lysine, leucine.

If desired, in another alternative embodiment, the di-or polyamine, which is not amino protected, can be reacted with 2 or more equivalents of a pentamethinium salt to form a di-or poly-pyridinium compound.

Also preferred primary amines are amines substituted with a furanosyl sugar moiety or an analogue of the furanosyl sugar moiety, optionally phosphorylated at the OH group or compromised with a protected hydroxyl group, while the protecting groups are benzyl, acetal, silyl and trityl or compromised with F or methoxy instead of the OH group. It is preferred to use furanosyl sugars or such analogues suitable for the synthesis of NAD or nicotinamide mononucleotides and analogues thereof.

The synthesis of NAD or nicotinamide mononucleotides and analogues thereof using furanosyl amines is described in the following references: kam, B.L. et al, Biochemistry 26(1987) 3453-3461; sicsic, S, et al, European Journal of Biochemistry 155(1986) 403-; kam, b.l. and Oppenheimer, n.j., Carbohydrate Research 77(1979) 275-; and US 4,411,995.

Preferred furanosylamines are the beta and alpha anomers of D and L ribose, xylose and arabinose.

Also preferred are cyclopentylamine, which is a carba analog of furanosylamine, such as β -D-ribofuranosylamine, 2 deoxyribofuranosylamine, or 2,3 dideoxyribofuranosylamine, i.e., (1R,2S,3R,4R) -2, 3-dihydroxy-4-hydroxymethyl-1-aminocyclopentane, (1S, 3R,4R) -3-amino-4-hydroxy-cyclopentanemethanol, or (1R-cis) -3-amino-cyclopentane-methanol.

In a more preferred embodiment of the process according to the invention, a pentamethinium salt is reacted with a primary amine, wherein the primary amine is (1R,2S,3R,4R) -2, 3-dihydroxy-4-hydroxymethyl-1-aminocyclopentane. 5-dimethyl-amino-4-methoxycarbonyl-penta-2, 4-dimethyl-dienylidene ammonium tetrafluoroborate and the primary amine react to form nicotinamide-carba nucleoside (3-methoxycarbonyl-1- ((1R, 2S,3R,4R) -2, 3-dihydroxy-4-hydroxymethyl-cyclopentyl) pyridinium chloride), which can be readily converted with ammonia to nicotinamide-carba nucleoside (3-carbamoyl-1- ((1R, 2S,3R,4R) -2, 3-dihydroxy-4-hydroxymethyl-cyclopentyl) pyridinium tetrafluoroborate. nicotinamide-carba nucleoside is a key compound for the synthesis of carba analogs of NAD. carba-NAD and its preferred uses are described in detail in WO 2007/012494. WO2007/012494 discloses in its entirety by incorporation Herein incorporated.

Further preferred substituted primary amines are selected from 3-aminotetrahydrofuran or protected 3-amino-pyrrolidines, e.g., (2R, 4R) -4-aminotetrahydrofuran-2-methanol, a heterocyclic analog of 2, 3-dideoxynucleosamine, cyclohexylamine and cyclohex-2-enylamine, e.g., 6-cyclic sugar analogs as disclosed in Goulioukina, N.et al, Helvetica Chimica Acta 90(2007) 1266-1278.

Preferred examples of phosphorylated aminosugars are (1R, 4S, 6S) -4-amino-6-hydroxy-2-cyclohexene-1-methanol-1- (dihydrogen phosphate), 2-amino-1, 5-anhydro-2-deoxy-6- (dihydrogen phosphate) D-altritol, 2-amino-1, 5-anhydro-2, 3-dideoxy-and 6- (dihydrogen phosphate) D-arabinose-hexitol.

As the skilled artisan will appreciate, primary amines with additional primary nucleophilic substituents can be used. In this case more nucleophilic groups must be protected by suitable protecting groups.

Protecting groups are well known in the art and are reviewed in standard texts (Greene, t.w., Protective groups in organic synthesis, John Wiley & Sons, Inc (1981) New York, chicchester, Brisbane, Toronto). Preferably, the amino group is protected with a boc-, phthalyl or trifluoroacetyl protecting group and the thiol group is protected as a disulfide.

In a more preferred embodiment, the method of the invention is used to bind other primary amines, such as an amino-modified TAMRA dye. The corresponding N-substituted methyl nicotinate can be obtained in good yield by cyclizing the pentamethinium salt with a mixture of 5- (and 6) - ((N- (5-aminopentyl) amino) carbonyl) -tetramethylrhodamine (under analogous conditions to the reaction with amino carba ribose).

The reactivity towards the 3-methoxycarbonylpyridinium system opens up the possibility of applying the cyclization reaction. In a more preferred embodiment, the N-substituted methyl or ethyl nicotinate formed in the method of the invention may be used as an optional linkage in a coupling process, for example coupling a biomolecule such as an oligonucleotide to an effector group such as a hapten, fluorescent or luminescent compound. The invention therefore also relates to the inclusion of an N-substituted methyl or ethyl nicotinate as linker.

The following examples are provided to aid the understanding of the present invention, the true scope of which is set forth in the following claims. It will be appreciated that modifications can be made to the method described without departing from the spirit of the invention.

Example (b):

example 1:

synthesis of 5-dimethylamino-4-methoxycarbonyl-penta-2, 4-dienylidene-dimethyl-ammonium tetrafluoroborate

Example 1.1: synthesis of methyl- (2E) -3- (3-dimethylamino) prop-2-enoate

To a solution of methyl propiolate (68.0ml, 0.764mol) in 700ml dry THF was added a solution of N, N-dimethylamine (392ml, 0.783mol) in 2M of the same solvent at room temperature over 1 hour. After removal of the solvent, the residue was dried in an evaporator for 1 hour (37 ℃ C., 10-20mbar) to give a pale yellow solid. The crushed solid was washed with n-hexane to give 93.0g (94%) of methyl- (2E) -3- (3-dimethylamino) propan-2-enoic acid ester which was pure by TLC and 1H NMR.

Example 1.2: synthesis of pyridinium tetrafluoroborate

Tetrafluoroboric acid (250ml, 2.00mol) was added to cold (0 ℃ C.) pyridine (157.7ml, 1.95mol) over 25 minutes to give a colorless precipitate. After the acid was completely added, the mixture was further stirred at the same temperature for 30 minutes. The reaction mixture was then filtered. The residue was washed twice with cold ethanol and dried under high vacuum for 12 hours to give 201.9g (60%) of pyridinium tetrafluoroborate as colorless crystals.

Example 1.3: synthesis of 5-dimethylamino-4-methoxycarbonyl-penta-2, 4-dienylidene-dimethyl-ammonium tetrafluoroborate

Pyridinium tetrafluoroborate (283.7g, 1.70mol) was added to a solution of methyl- (2E) -3- (3-dimethylamino) prop-2-enoate in 442.5ml acetic anhydride/acetic acid (2: 1). The resulting suspension was cooled to 0 ℃ and 3-dimethylaminopropenal (169.9ml, 1.70mol) was added slowly (3h) with ice-bath cooling under vigorous stirring to give a yellow-brown precipitate. After further stirring at room temperature for 2 hours, the reaction mixture was filtered. The residual solid was washed several times with diethyl ether and dried under reduced pressure. Recrystallization from isopropanol/ethanol (2: 1) gave 326.7g (65%) of quintocet-onium salt as yellow crystals.

Example 2:

synthesis of 3-amino-5-hydroxymethyl-cyclopentane-1, 2-diol

Addition of a 1M solution of KOH in EtOH (54.5ml, 54.5mmol) to a solution of cooled (0 ℃ C.) hydrochloride (10.0g, 54.5mmol) in 540ml EtOH. After stirring for 15 minutes at room temperature, the colorless precipitate formed was removed by filtration. The filtrate was concentrated under reduced pressure. The remaining oil was dried in an evaporator (1h, 40 ℃) to give 9.01g (112%) of amino carba ribose as a pale yellow oil. The product obtained was used in the next step without further purification.

Example 3:

synthesis of 1- (2, 3-dihydroxy-4-hydroxymethyl-cyclopentyl) -3-methoxycarbonyl-pyridinium methanesulfonate

Vinimidinium salt (298.1g, 1.00mol) was dissolved in 1500ml DMF and 1 equivalent of methanesulfonic acid (65.02ml, 1.00mol) was added. The mixture was continuously and very slowly (over 5 h) dropped into 1250ml of a refluxing solution (90 ℃) of methanol of 3-amino-5-hydroxymethyl-cyclopentane-1, 2-diol (165.3g, 0.90mol) and 3-amino-5-hydroxymethyl-cyclopentane-1, 2-diol (25.8g, 0.15 mol). After complete addition of the vincimidine onium salt solution, the reaction mixture was cooled to room temperature and 0.15 equivalents of methanesulfonic acid was added. The mixture was stirred at the same temperature for 12 hours. After removal of the solvent under reduced pressure, a reddish brown oil was obtained which was further dried for 3h (45 ℃ C., 4 mbar). Yield: 693.0g (191%, containing salt and a large amount of solvent).

Example 4:

3-carbamoyl-1- (2, 3-dihydroxy-4-hydroxymethyl-cyclopentyl) -pyridinium methanesulfonate

The crude 1- (2, 3-dihydroxy-4-hydroxymethyl-cyclopentyl) -3-methoxycarbonyl-pyridinium methanesulfonate of example 3 was rapidly converted to the corresponding amide without further purification.

Crude 1- (2, 3-dihydroxy-4-hydroxymethyl-cyclopentyl) -3-methoxycarbonyl-pyridinium methanesulfonate 118.3g, 173.7mmol) was dissolved in 100.0ml methanol. After addition of methanolic ammonia (7M, 350.0ml, 2.45mol), the reaction mixture was stirred for 2.5 hours. After removal of the solvent under reduced pressure, a reddish brown oil was obtained which was further dried for 3 hours (40 ℃ C., 10 mbar). The crude product was pre-purified with activated carbon and then used directly for the synthesis of cNAD (WO 2007/012494).

Example 5:

synthesis of 3-N, N-dimethylcarbamoyl-1- (2, 3-dihydroxy-4-hydroxymethyl-cyclopentyl) -pyridinium methanesulfonate

The 3-N, N-dimethylcarbamoyl-1- (2, 3-dihydroxy-4-hydroxymethyl-cyclopentyl) -pyridinium-methanesulfonate was obtained analogously to the 3-carbamoyl-1- (2, 3-dihydroxy-4-hydroxymethyl-cyclopentyl) -pyridinium-methanesulfonate obtained by reaction of the methyl ester from example 3 with dimethylamine in THF.

Example 6:

coupling Vinimidine onium salts to TAMRA dyes

An N-TAMRA-substituted nicotinate is formed by reaction of a vincimidine onium salt with a modified TAMRA dye.

Cyclization was performed with amino-modified TAMRA dyes.

Amino-modified TAMRA dye (see mixture of 5-and 6-isomers above) (19.8mg, 35.93. mu. mol) was dissolved in MeOH HCl (0.125M, 201. mu.l, 25.15. mu. mol). The mixture was heated at 65 ℃ and a solution of vincimidine onium salt (10.7mg, 35.93. mu. mol) in MeSO3H (0.154M in MeOH/DMF (1: 1), 233. mu.l, 35.93. mu. mol) was added slowly over 2.5 hours at the same temperature. After addition of the vinimidine onium salt solution, the reaction mixture was stirred at room temperature for 16 hours. The solvent was removed under reduced pressure and purified by HPLC (Hypersil ODS) using an acetonitrile/water gradient. The pure product was dissolved in methanol HCl and evaporated to dryness under reduced pressure to yield 16.6mg (60%) of TAMRA pyridinium conjugate.

MS：ESI：M+＝636.98(24)

Claims (8)

1. A method of synthesizing an N-substituted carboxylated pyridinium compound comprising the steps of:

a) a pentamethinium salt is provided, as shown in formula I

Formula I:

wherein X^-Is a counter-ion to the ion of the compound,

r1 is alkoxy, selected from the group consisting of O-methyl, O-ethyl, O-propyl, and O-isobutyl, and

r2 to R5 are independently methyl or ethyl;

b) reacting the pentamethine onium salt of step (a) with a primary amine of formula II,

formula II:

wherein R6 is a linear, branched, or cyclic optionally substituted alkyl, wherein the alkyl is linear C1-C6 alkyl, or branched C3-C6 alkyl, or cyclic C5-C6 alkyl, or the substituted alkyl is substituted linear C1-C6 alkyl, or substituted branched C3-C6 alkyl, or substituted cyclic C5-C6 alkyl, and the substituent on the substituted alkyl does not affect the cyclization reaction with the pentamethinium salt of step (a);

c) to give an N-substituted pyridinium compound of the formula III

Formula III:

wherein X^-R1, and R6 are as described above.

2. The process of claim 1, wherein in step (b) the pentamethinium salt of step (a) is reacted with the primary amine in the presence of the corresponding protonated amine of the primary amine.

3. The process of claim 2, wherein the ratio of primary amine to its corresponding protonated amine is from 2:1 to 1: 50.

4. The process of claim 2, wherein the ratio of primary amine to its corresponding protonated amine is from 1:1 to 1: 20.

5. The method of claim 1, wherein R1 is OCH 3.

6. The method of claim 1, wherein R2 through R5 are methyl.

7. The method of any one of claims 1-6, wherein the primary amine of formula II is 2, 3-dihydroxy-4-hydroxymethyl-1-aminocyclopentane.

8. The process of any one of claims 1-6, wherein the primary amine of formula II is (1R,2S,3R,4R) -2, 3-dihydroxy-4-hydroxymethyl-1-aminocyclopentane.