WO2025132868A1

WO2025132868A1 - L-carnitine and valproic acid drug-drug co-crystal

Info

Publication number: WO2025132868A1
Application number: PCT/EP2024/087514
Authority: WO
Inventors: Roberto Gobetto; Michele CHIEROTTI; Angelo GALLO; Federica Bravetti; Simone Bordignon
Original assignee: Universita degli Studi di Torino
Current assignee: Universita degli Studi di Torino
Priority date: 2023-12-21
Filing date: 2024-12-19
Publication date: 2025-06-26
Anticipated expiration: 2026-06-21

Abstract

The present patent application relates generally to crystals, and more specifically co- crystals of L-carnitine and valproic acid, in particular the L-carnitine and valproic acid drug-drug co-crystal, Compound (I), and methods of preparing such compounds for using the co-crystals in the treatment of various diseases, disorders, and conditions.

Description

DESCRIPTION

L-CARNITINE AND VALPROIC ACID DRUG-DRUG CO-CRYSTAL

FIELD OF THE INVENTION

The present patent application relates generally to crystals, and more specifically cocrystals of L-carnitine and valproic acid, in particular the L-carnitine and valproic acid drugdrug co-crystal, Compound (I) or VPA*CNT, and methods of preparing such compounds for using the co-crystals in the treatment of various diseases, disorders, and conditions.

valproic acid L-carnitine (VPA) (CNT)

BACKGROUND

Valproic acid (VPA) (2-propylpentanoic acid) is a synthetic substance, employed as an anticonvulsant drug for the treatment of various forms of both generalized and partial epilepsy (M. Romoli et al., Curr. Neuropharmacol., 2019, 17, 926-946; V. Prakash Giri et al., J. Clin. Diagn. Res., 2016, 10, FC01-FC04; R. H. Mattson et al. N. Engl. J. Med., 1992, 327, 765- 771 ; M. Prasad et al., Cochrane Database of Systematic Reviews, 2014, 9, CD003723; C. J. Phiel et al., J. Biol. Chem., 2001 , 276, 36734-36741), as well as for the treatment of migraine episodes (M. Linde et al., Cochrane Database of Systematic Reviews, 2013, 6, CD010611 ; S. Kinze etal., Headache, 2001 , 41, 774-778; E. Vatzaki etal., J. Headache Pain, 2018, 19, 68). In general, VPA-based drugs are administered in the form of sodium salts (R. M. Pinde et al., Avery, Drugs, 1977, 13, 81-123; A. Zawab et al., Australian Prescriber, 2014, 37, 124-127) or amide derivatives (H. S. White et al., Epilepsia, 2012, 53, 134-146; S. Andreu et al., Viruses, 2020, 72, 1356), with the aim of achieving a solid form of the active pharmaceutical ingredient (API), which is liquid in ambient conditions. As of lately, VPA has been put under the spotlight as a promising drug in the treatment of mood disorders, including manic episodes (J. Jochim et al., Cochrane Database of Systematic Reviews, 2019, 70, CD004052) and bipolar disorder (L. A. Smith et al., J. Affective Disord., 2010, 722, 1-9; A. Cipriani et al., Cochrane Database of Systematic Reviews, 2013, 70, CD003196).

The most significant issue with the administration of VPA is associated with a severe carnitine deficiency in patients treated with this drug (Y. Chan et al., Hum. Exp. Toxicol., 2007, 26, 967-969; A. Verrotti et al., Int. J. Clin. Lab. Res. 1999, 29, 36-40).

L-carnitine (CNT) is an amino acid that plays a key role in the metabolism of lipids (N. Longo et al., Biochim. Biophys. Acta, Mol. Cell Res., 2016, 1863, 2422-2435; A. P. Isaeva et al., Clin. Nutr., 2018, 37, S38-S39). This frequently leads to the administration of CNT in combination with VPA (P. E. R. Lheureux et al., Clin. Toxicol., 2009, 47, 101-111 ; J. Y. Raskind etal., Ann. Pharmacother. 2000, 34, 630-638; P. E. R. Lheureux et al., Critical Care, 2005, 9, 431-440).

CNT is known to crystallize in two distinct polymorphic phases, both in the monoclinic P2i space group; the two polymorphs are easily distinguished through their Z’ value, i.e. , the number of independent molecules of CNT in the unit cell of the crystal structure. Indeed, while the most common crystal form of CNT has a Z’ value of 1 , the other one has Z’ = 2 (R. D.

Gandour et al., Bioorg. Chem., 1985, 73, 197-208). Although valproic acid is a therapeutically active pharmaceutical ingredient, it is an oil that is difficult to formulate and use in the preparation of dosage forms suitable for human or veterinary use. Pharmaceutical and pharmacological advantages are obtained when therapeutic dosage forms are prepared from alkali metal or alkaline earth metal salts of valproic acid.

CNT is supplied to the body through both endogenous synthesis (about 25% of the adult daily requirement) and food intake (about 75% of the adult daily requirement). The main dietary source of CNT is meat; beef and lamb provide the most dietary CNT (fruits and vegetables provide only traces of L-carnitine). Within the human body, the major sites of CNT biosynthesis are the liver and kidney, as well as the brain and testes. Biosynthesis requires lysine, methionine, vitamin C, iron, vitamin B6, and niacin.

CNT functions as a requisite mediator of acyl transport and accepts acyl groups from a variety of acylCoA derivatives in cells and tissues throughout the body. In humans, the transport activity of L-carnitine is particularly important in the functioning of muscles, such as skeletal muscles and the heart. Both types of tissues are dependent on fatty acid metabolism for energy supply, and L-carnitine mediates the translocation of fatty acyl groups across mitochondrial membranes to the sites of oxidation in the mitochondria. In addition, CNT shuttles short chain fatty acids from inside the mitochondria to the cytosol. Other physiological roles of CNT include mitochondrial long-chain fatty acid oxidation, buffering of the mitochondrial acyl CoA/CoA couple, scavenging acyl groups, peroxysomal fatty acid oxidation, branched-chain amino acid oxidation, and membrane stabilization.

Because CNT functions as a requisite mediator of acyl transport in the body, CNT deficiency is a serious physiological disorder. Individuals who suffer from CNT deficiency are afflicted with muscle weakness (myasthenia), accompanied by an accumulation of lipids in specific types of muscle fibers. Severe CNT deficiency may present as myasthenia gravis. Individuals who suffer from systemic CNT deficiency and also secondary CNT deficiency associated with organic acidemias may experience vomiting, stupor, confusion and in severe or prolonged occasions of systemic CNT deficiency accompanied by stressful stimuli, coma in encephalopathic episodes.

Given the facts that valproate induces liver steatosis and CNT deficiency, that CNT is a requisite mediator of acyl transport in the body, and that neonates and young children lack the ability to synthesize CNT (vide infra), it is not surprising that young age and polytherapy including valproate are the primary risk factors for valproate-induced CNT deficiency and valproate- related hepatic failure.

There are, however, known difficulties in formulating CNT. For example, it is known that CNT is hygroscopic. The hygroscopicity of CNT causes a lack of storability of the solid substance and of simple powder mixtures prepared therefrom, and causes problems such as inadequate flowability during further formulating, processing, and manufacturing of orally administrable dosage forms of pure solid CNT or powdered mixtures containing CNT for use in food, nutritional or dietary supplements for humans or other mammals, animal feed or dietary supplements, or drugs for human or veterinary use. However, oral dosage forms represent the preferred dosage forms, inasmuch as they make it particularly easy for users to take the active ingredient and comply with optimal dosage regimens.

Further, it is known that CNT exhibits a distinctly repugnant malodor and a distinctly objectionable taste after ingestion. The noxious odor and taste render ingestion of oral dosage forms of CNT difficult and interfere with compliance to optimal dosage regimens. Thus, there is a significant unmet need for a form of CNT that is free from noxious odor or taste that can be administered to address CNT deficiency.

Patients receiving conventional valproate compositions often must conform to complex dosing regimens. In addition to valproate, individuals may be taking other medications. Therefore, the addition of a dosage of supplemental CNT often adds a new level of complexity to an already complicated dosing regimen for these patients.

Further, although there are numerous case reports and case series in the literature documenting valproate-induced CNT deficiency, there are very few reports of the carnitine levels in the general patient population. CNT is not routinely monitored in patients receiving valproate, and unrecognized CNT deficiency may develop unexpectedly in these subjects. A consideration of all of the facts presented heretofore indicates clearly that there is a significant unmet need for a composition that concomitantly provides therapeutic quantities of both valproate and CNT. The present invention remedies this need.

SUMMARY OF THE INVENTION

The present invention provides a co-crystal comprising L-carnitine and valproic acid, Compound (I).

In some embodiments, Compound (I) co-crystal is characterized by having an XRPD pattern comprising peaks at angles 2-theta of about 4.68, 9.44, 12.13, 14.66, 15.59, 18.23, 19.05, and 19.89 degrees.

In some embodiments, Compound (I) co-crystal is characterized by having an XRPD pattern substantially as shown in FIG. 7.

In some embodiments, Compound (I) co-crystal is characterized by having an IR spectrum comprising peaks at wavenumbers of about 2956, 2934, 2873, 1629, 1197, and 1096 cm’¹.

In some embodiments, Compound (I) co-crystal is characterized by having an IR spectrum substantially as shown in FIG. 1.

In some embodiments, Compound (I) co-crystal is characterized by having a ¹H MAS SSNMR spectrum comprising peaks at chemical shifts of about 18.9, 8.0, and 4.6 ppm.

In some embodiments, Compound (I) co-crystal is characterized by having a ¹H MAS SSNMR spectrum substantially as shown in FIG. 2.

In some embodiments, Compound (I) co-crystal is characterized by having a ¹³C CPMAS SSNMR spectrum comprising peaks at chemical shifts of about 182.9, 175.3, 67.5, 48.1 , and 14.9 ppm.

In some embodiments, Compound (I) co-crystal is characterized by having a ¹³C CPMAS SSNMR spectrum substantially as shown in FIG. 3.

In some embodiments, Compound (I) co-crystal is characterized by having a ¹⁵N CPMAS SSNMR spectrum comprising peaks at chemical shifts of about 49.1 ppm.

In some embodiments, Compound (I) co-crystal is characterized by having a ¹⁵N CPMAS SSNMR spectrum substantially as shown in FIG. 4.

The aim of the present invention is to obtain a pure solid phase of liquid VPA, thus one that is easier and less invasive to be administered to patients, and at the same time one that acts as a convenient strategy to fight the common CNT deficiency induced by VPA-based treatments. Moreover, the present invention provides a new crystal form, Compound (I) that potentially allows for the consumption of a single medication, which in turn leads to the decrease of the pills burden in patients. This minimizes mistakes by patients in the adherence to the therapy, which often causes complicated schedules for assumptions. The consequences of a wrong approach to pharmacotherapies were estimated to cost about $100 billion per year, due to a larger number of hospitalizations and deaths (J. J. Klobusicky et al., AMIA Annu. Symp. Proc. 2015, 2015, 766-774).

The present invention will be now described in a detailed way with reference to the figures with their annexed pictures, in which:

- Figure 1 shows the FTIR-ATR spectra of Compound (I) and pure VPA and CNT.

- Figure 2 shows the ¹H (400.23 MHz) MAS spectrum of Compound (I), collected at probe temperature at 32 kHz;

- Figure 3 shows the ¹³C (100.64 MHz) CPMAS spectra of Compound (I) and of Compound (I), NaVPA, pure CNT and L-carnitine hydrochloride (CNT HCI), collected at probe temperature at 12 kHz;

- Figure 4 illustrates the ¹⁵N (40.56 Hz) CPMAS spectra of Compound (I) and of CNT at probe temperature at 9 kHz;

- Figure 5 shows the 2D ¹H (400.23 MHz)-¹³C (100.64 MHz) short-range HETCOR spectrum of Compound (I), recorded at probe temperature at 12 KHz.

- Figure 6 shows the 2D ¹H (400.23 MHz)-¹³C (100.64 MHz) long-range HETCOR spectrum of Compound (I), recorded at probe temperature at 12 KHz (top) and a schematization of the main correlations deduced from the long-range HETCOR spectrum of Compound (I) (bottom). The dashed box (magnification of 4x) highlights weaker, but significant, correlations between Ha and C2, C5/6/7 and C3. Bottom: scheme of the main correlations observed in the ¹H-¹³C long-range HETCOR spectrum (arrows) and the deduced hydrogen bonds between VPA and CNT (dashed lines).

- Figure 7 shows the XRPD pattern of Compound (I). - Figure 8 shows the Rietveld plot for Compound (I).

- Figure 9 shows the asymmetric unit of Compound (I);

- Figure 10 shows the unit cell of Compound (I): a) view direction [010] and b) view direction [001],

In the present patent application, by “co-crystal” is meant a single-phase crystalline material including two or more compounds, in a definite stoichiometric ratio, in its asymmetric unit, among which at least two display weak interactions with each other and at least one is a co-former. By weak interaction is meant an interaction such as hydrogen bonds, van derWaals forces, TT-TT interactions; covalent and ionic bonds are not considered.

Molecular salts, i.e. , supramolecular adducts in which a protonic transfer has occurred from an acid to a basic molecule, and weak interactions exist between the ionized molecules, are included in the definition of “co-crystal”.

By “drug-drug co-crystal” is meant a co-crystal in which at least two of the molecules which are in the crystal lattice and are bound together through weak interactions, are APIs.

In this patent application, a “co-former” is intended as a molecule which is able to form a co-crystal with an API.

The stoichiometric ratio between VPA and CNT in Compound (I) is 1 :1.

The co-crystal of the present invention can be easily prepared through mechanical grinding in an agate mortar. Due to the high hygroscopicity of pure CNT, the synthesis is more efficient if it is carried out in a dry atmosphere.

The product was characterized by combining experimental techniques known for giving complementary information about powder samples such as: IR (ATR) spectroscopy, powder X-ray diffraction (PXRD), solid-state nuclear magnetic resonance (¹H MAS, ¹³C and ¹⁵N CPMAS, ¹H-¹³C FSLG and FSLG-LGCP experiments).

By combining XRPD with SSNMR data, and through the employment of DFT, it was possible to solve and optimize the crystal structure of Compound (I) without the need of a single crystal.

The structure is characterized by a peculiar /?i(10) hydrogen-bonded ring, which involves the carboxylic/carboxylate moieties of the two constituents, and the alcoholic OH group of CNT, as confirmed by the 2D correlations observed in the long-range HETCOR experiment, which perfectly agree with the crystal structure obtained from XRPD data.

The present invention is characterized by the following features: it is a new crystalline phase, not reported previously; it is a crystalline phase of VPA, which is liquid at ambient conditions. This allows for an improved oral administration of the drug; besides VPA, it includes CNT, which acts as an antidote to an extremely common side-effect of VPA-based therapies. Consequently, a better pill management is possible. it presents a much more tolerable odor with respect to pure CNT, improving compliance from patients who follow CNT-based therapies.

The invented co-crystal and its pharmaceutical composition can be employed as a medicament especially in the treatment of epileptic seizures and mood disorders.

Also within the scope of this invention are Compound (I) compositions having specific bulk densities or tap densities, and Compound (I) compositions having specific particle sizes. Further included within the scope of this invention are Compound (I) compositions coated with pharmaceutically acceptable materials intended to modify the release and/or bioavailability of Compound (I) of the present invention (e.g., Eudragit, microcrystalline cellulose, hydroxypropylmethylcellulose phthalate, and so forth). According to the methods of the present invention, Compound (I) is administered, alone or in combination with other therapeutically active or inactive substances, as a therapeutically effective and biologically available (i.e. , bioavailable) source of L-carnitine and valproic acid that is concomitantly useful for the treatment of neurological, immunological, and viral-related disorders and for the prevention and/or treatment of L-carnitine deficiency.

The term "excipient material" means any compound forming a part of the formulation, which is not intended to have independent biological activity, and which is added to a formulation to provide specific characteristics to the dosage form, including providing protection to the active ingredient from chemical degradation, facilitating release of a tablet or caplet from the contact surfaces of manufacturing equipment, and so forth.

The terms "treating" and "treatment" and the like are used herein to generally mean obtaining a desired pharmacological and physiological effect. The effect may be prophylactic in terms of preventing or partially preventing a disease, symptom or condition thereof and/or may be therapeutic in terms of a partial or complete cure of a disease, condition, symptom or adverse effect attributed to the disease. The term "treatment" as used herein encompasses any treatment of a disease in a mammal, particularly a human and includes: (a) preventing the disease from occurring in a subject which may be predisposed to the disease but has not yet been diagnosed as having it; (b) inhibiting the disease or arresting its development; or (c) relieving the disease, causing regression of the disease and/or its symptoms or conditions. The phrase "therapeutically effective" is intended to qualify the amount of Compound (I) for use in the orally or intravenously administered therapy which will achieve the goal of providing a biologically available (i.e., bioavailable) concentration of the drug valproic acid to effectively reducing or preventing, for example, a neurological, immunological, or viral-related disorder, while avoiding adverse side effects typically associated with valproic acid, sodium valproate compositions, or other valproate salts.

Included within the scope of this invention is a method of treating neurological disorders, immune disorders, or viral-related disorders in a warm-blooded animal using pharmaceutical compositions comprising Compound (I) of the present invention and a suitable pharmaceutical carrier.

For the purpose of this disclosure, a warm-blooded animal is a member of the animal kingdom which includes but is not limited to mammals and birds. The most preferred mammal of this invention is human.

In general, the pharmaceutical compositions of this invention can be prepared by conventional techniques, as are described in Remington's Pharmaceutical Sciences, a standard reference in this field [Gennaro AR, Ed. Remington: The Science and Practice of Pharmacy. 20<th> Edition. Baltimore: Lippincott, Williams & Williams, 2000], For therapeutic purposes, the active components of this combination therapy invention are ordinarily combined with one or more adjuvants appropriate to the indicated route of administration. If administered per os, the components may be admixed with lactose, sucrose, starch powder, cellulose esters of alkanoic acids, cellulose alkyl esters, talc, stearic acid, magnesium stearate, magnesium oxide, sodium and calcium salts of phosphoric and sulfuric acids, gelatin, acacia gum, sodium alginate, polyvinylpyrrolidone, and/or polyvinyl alcohol, and then tabletted or encapsulated for convenient administration. Such capsules or tablets may contain a controlled-release formulation as may be provided in a dispersion of active compound in hydroxypropyl methylcellulose. Solid dosage forms can be manufactured as sustained release products to provide for continuous release of medication over a period of hours. Compressed tablets can be sugar coated or film coated to mask any unpleasant taste and protect the tablet from the atmosphere, or enteric coated for selective disintegration in the gastrointestinal tract. Both the solid and liquid oral dosage forms can contain coloring and flavoring to increase patient acceptance.

Formulations for parenteral administration may be in the form of aqueous or nonaqueous isotonic sterile injection solutions or suspensions. These solutions and suspensions may be prepared from sterile powders or granules having one or more of the carriers or diluents mentioned for use in the formulations for oral administration. The components may be dissolved in water, polyethylene glycol, propylene glycol, ethanol, corn oil, cottonseed oil, peanut oil, sesame oil, benzyl alcohol, sodium chloride, and/or various buffers. The indicated formulations can contain compatible auxiliaries and excipients, such as anti-oxidants, preservatives, stabilizing agents, emulsifiers, salts for influencing the osmotic pressure, and/or buffer substances. Other adjuvants and modes of administration are well and widely known in the pharmaceutical art.

Pharmaceutical compositions for use in the treatment methods of the invention may be administered orally or by intravenous administration. Oral administration of the therapy is preferred. Dosing for oral administration may be with a regimen calling for single daily dose, or for a single dose every other day, or for multiple, spaced doses throughout the day.

Further characteristics of the present invention are discussed in the following description of some purely explicative but not exhaustive examples. EXPERIMENTAL SECTION

In the following examples the synthesis and the characterization of the powder of Compound (I) are reported. The peculiarity of this co-crystal, which is hereby defined as a “drug-drug co-crystal”, is the simultaneous presence of VPA and CNT, both APIs, inside the crystal lattice. The sample was obtained through the mixing and grinding of the co-formers.

The sample was studied by combining solid-state experimental techniques, known for providing complementary information about powder samples: powder X-ray diffraction (PXRD), solid-state nuclear magnetic resonance (SSNMR), and infrared spectroscopy (FTIR- ATR).

PXRD analyses were carried out on a STOE (Germany) stadi-P diffractometer; SSNMR spectra were collected on a Bruker (Germany) Avance II 400 Ultra Shield NMR spectrometer; IR (ATR) spectra were acquired with a Bruker (Germany) Equinox 55 instrument.

Example 1

Preparation of Compound (I)

VPA and CNT were purchased from Sigma Aldrich (purity 99%) and Alfa Aesar (purity >98%), respectively, and they were used without further purification steps. By means of SSNMR, the value of Z’ for the employed CNT was assessed to be 1 , which led to the recognition of the polymorphic phase represented by the commercial batch (R. D. Gandouref a/., Bioorg. Chem., 1985, 13, 197-208). The co-crystal was obtained in a 1 :1 stoichiometric ratio for the two APIs, through mechanochemical methods (grinding).

Preparation of Compound (I) drug-drug co-crystal By grinding CNT (249 mg, 1.5 mmol) in the presence of VPA (240 pL, 1.5 mmol), with no solvent added, in an agate mortar, in a stoichiometric ratio of 1 :1 , at room temperature, for 10 minutes, Compound (I) was obtained in the form of a light-yellow powder.

The product was characterized by: SSNMR (Bruker Avance II 400 Ultra Shield), PXRD (STOE stadi-P), and IR (ATR) (Bruker Equinox 55) spectroscopy. The crystal structure was solved from powder data and refined by DFT optimization.

Analysis

Fourier transform infrared spectroscopy in attenuated total reflection (FTIR-ATR)

FTIR-ATR spectroscopy was leveraged exclusively for a screening purpose, to assess the obtainment of a product different from either starting material. Figure 1 shows a comparison among the ATR spectra of Compound (I), and pure VPA and CNT .

Notably, some peaks in the spectra appear to be superposable, e.g., those falling right below 3000 cm^-1; nonetheless, several other signals fall at different wavenumbers in the spectrum of Compound (I) than in those of pure VPA and CNT. This was enough to distinguish Compound (I) from a physical mixture of pure VPA and CNT.

Solid-state nuclear magnetic resonance (SSNMR)

The data obtained by SSNMR analysis (¹H, ¹³C and ¹⁵N) are listed in Table 1 which reports experimental and computed ¹³C CPMAS, ¹H MAS and ¹⁵N CPMAS chemical shifts, and the respective RMSE values. As for the atoms’ numbering, please refer to the structures illustrated above (left: VPA; right: CNT).

Table 1. Experimental (EXP) and calculated (CALC) ¹³C, ¹H and ¹⁵N SSNMR chemical shifts for Compound (I), and corresponding RMSE values.

The SSNMR ¹H MAS spectrum of Compound (I) is shown in Figure 2; ¹³C CPMAS spectra for Compound (I), pure CNT, pure sodium valproate (NaVPA) and pure L-carnitine hydrochloride (CNT HCI) are reported in Figure 3; ¹⁵N CPMAS spectra for Compound (I) and pure CNT are shown in Figure 4.

The ¹H MAS spectrum of Compound (I) (Figure 2) presents four broad signals. The one in the hydrogen-bond region, at 18.9 ppm, can be assigned with good certainty to Ha and such a high chemical shift value suggests that Ha is involved in a very strong hydrogen bond (P. Cerreia Vioglio et al., Advanced Drug Delivery Reviews, 2017, 117, 86-110). The signal at 8.0 ppm can thus be ascribed to the only remaining unassigned proton, Hp. The two broad signals in the aliphatic region of the spectrum, at 1.2 and 3.8 ppm, are produced by the overlapping of the aliphatic resonances of both VPA and CNT. It is reasonable to assume that the signals of the aliphatic chains of VPA fall under the signal at lower ppm, whereas the signals of the protons of CNT are included in that at higher ppm, given their proximity to oxygen and nitrogen atoms and to the C=O group. These assignments are further confirmed by the 2D spectra (see Figures 5 and 6, top).

The overlay of the ¹³C CPMAS spectra of CNT, NaVPA, CNT HCI and Compound (I) is shown in Figure 3. As VPA is liquid at ambient conditions, Compound (I) has been compared to its sodium salt NaVPA, which is among the most frequently administered solid forms of VPA (R. M. Pinder et al, Drugs, 1977, 13, 81-123; A. Zawabet al., Australian Prescriber, 2014, 37, 124-127). It is worth noting that from the ¹³C CPMAS spectrum of Compound (I) it is clear that Z’ is equal to 1 , since only one set of signals is observed, i.e. one molecule of CNT and one of VPA inhabit the asymmetric unit of Compound (I). Secondly, it can be noted that Compound (I) presents shifted signals with respect to those of the reagents. Specifically, the fact that almost all the signals of Compound (I) are not superposable with those of the reactants suggests that the obtained Compound (I) is pure, not containing traces of unreacted reagents. The signals that significantly change in the spectrum of Compound (I) with respect to the reactants are the ones at:

34.9 and 36.5 ppm, related to C3’ and C6’; 54.1 ppm, related to C5/6/7;

65.1 and 67.5 ppm, related to C3 and C4;

182.9 ppm, related to CT.

In particular, the signal changes related to C1 and CT provide important information on the interactions established between the two molecules in Compound (I). The signal related to CT shows a noticeable shift at lower ppm with respect to that of the carboxylate in NaVPA, while C1 does not change significantly from the pure CNT spectrum. This can be explained by assuming the establishment of a hydrogen bond involving a proton transfer between CT and C1 . This transfer affects mainly the signal of CT, which, despite falling at lower ppm than in NaVPA, is still consistent with a carboxylate group (P. Cerreia Vioglio et al., Advanced Drug Delivery Reviews, 2017, 117, 86-110), and this is further justified by the tendency of the carboxylate groups of inorganic salts to resonate at lower frequencies than in their molecular- salt counterparts. On the other hand, the fact that the signal of C1 does not change could be due to the formation of a dimer between CNT and VPA, involving C1 , CT and the OHp group. Indeed, a signal a 175.3 ppm is consistent with a carboxylic group involved in a very strong hydrogen bond (P. Cerreia Vioglio et al., Advanced Drug Delivery Reviews, 2017, 117, Sel l 0). This hypothesis was further confirmed by the 2D spectra (see Figures 5 and 6, top).

As for the ¹⁵N analyses, Figure 5 shows how the only nitrogen atom in the system falls at 49.1 ppm both in pure CNT and in Compound (I). This indicates that the nitrogen stays basically unaffected by the formation of Compound (I) (P. Cerreia Vioglio et al. , Advanced Drug Delivery Reviews, 2017, 117, 86-110), which is not surprising, since, being the nitrogen atom involved in a permanent quaternary moiety, it is not available for establishing hydrogen bonds. Finally, two 2D SSNMR spectra were acquired, namely ¹H-¹³C short-range (Figure 5) and long-range (Figure 6, top) experiments. The former is helpful in assigning the majority of the signals observed in the ¹H MAS spectrum; indeed, correlations between ¹³C and ¹H signals are visible if the corresponding ¹³C and ¹H nuclei are covalently bonded. As for the long-range experiment, correlations appear also for ¹H-¹³C couples that are not covalently bonded, but are spatially close, nonetheless, providing invaluable insight into the structural features of the material. Specifically, it can be seen how Ha correlates with both CT and C1 , which suggests the formation of a hydrogen bond between the carboxylic and the carboxylate groups of VPA and CNT. Furthermore, the correlations between H with both CT and C1 suggest the formation of an

hydrogen-bonded ring, as showed in Figure 6 (bottom). The interactions shown in Figure 6 (bottom) are also confirmed by the weak cross-peaks between CT and H2 and H3 of CNT, which in the proposed configuration are at a sufficiently short distance from CT to allow these signals to appear.

Most notably, the correlations between Ha and C2, C5/6/7 and C3, highlighted in the dashed box, strongly indicate that the protonic transfer hypothesized from the analysis of the ¹³C CPMAS spectrum has indeed occurred, leading to the recognition of Compound (I) as a molecular salt, in which VPA is deprotonated, while CNT is positively charged, instead of zwitterionic.

Crystal structure from PXRD

A pure sample of Compound (I) was obtained by replicating the procedure described in Example 1 (see above) inside a glove-box, to prevent CNT deliquescence; it was thus measured with XRPD. The obtained diffractogram is shown in Figure 7. The powder pattern could be indexed in a monoclinic cell, with the P2i (4) space group. The crystal structure was solved by a direct-space method and subjected to a Rietveld refinement. The Rietveld plot is shown in Figure 8. All crystallographic information is reported in Table 2. All reflections observed in the powder pattern are listed below.

Table 2. Crystallographic information for the crystal structure of Compound (I).

The asymmetric unit of Compound (I) is shown in Figure 9. The unit cell (Figure 10a-b) is characterized by the simultaneous presence of one independent VPA molecule and one of CNT. These two molecules interact to form an 7?2 (1°) hydrogen-bonded ring, through the establishment of two hydrogen bonds between the carboxylate group of VPA, the carboxylic moiety and the alcoholic OH group of CNT.

Herein below (Table 3) the reflections observed in the XRPD pattern of the Compound (I) drug-drug co-crystal structure are reported.

Table 3. 20 degree values for the reflections observed in the XRPD pattern of Compound (I).

4.76 12.19 14.41 14.73 16.44 18.21

9.52 14.30 14.70 15.66 18.13 18.30

Claims

1. A co-crystal comprising valproic acid and L-carnitine, Compound (I).

2. Compound (I), according to claim 1 , characterized by having an XRPD pattern comprising peaks at angles 2-theta of about 4.68, 9.44, 12.13, 14.66, 15.59, 18.23, 19.05, and 19.89 degrees.

3. Compound (I), according to claims 1-2, characterized by having an XRPD pattern substantially as shown in FIG. 7.

4. Compound (I), according to claims 1-3, characterized by having an IR spectrum comprising peaks at wavenumbers of about 2956, 2934, 2873, 1629, 1197, and 1096 cm^-1.

5. Compound (I), according to claims 1-4, characterized by having an IR spectrum substantially as shown in FIG. 1.

6. Compound (I), according to claims 1-5, characterized by having a ¹H MAS SSNMR spectrum comprising peaks at chemical shifts of about 18.9, 8.0, and 4.6 ppm.

7. Compound (I), according to claims 1-6, characterized by having a ¹H MAS SSNMR spectrum substantially as shown in FIG. 2.

8. Compound (I), according to claims 1-7, characterized by having a ¹³C CPMAS SSNMR spectrum comprising peaks at chemical shifts of about 182.9, 175.3, 67.5, 48.1 , and 14.9 ppm.

9. Compound (I), according to claims 1-8, characterized by having a ¹³C CPMAS SSNMR spectrum substantially as shown in FIG. 3.

10. Compound (I), according to claims 1-9, characterized by having a ¹⁵N CPMAS SSNMR spectrum comprising peaks at chemical shifts of about 49.1 ppm.

11. Compound (I), according to claims 1-10, characterized by having a ¹⁵N CPMAS SSNMR spectrum substantially as shown in FIG. 4.

12. Process for preparing Compound (I) according to claims 1-11 , comprising grinding CNT in presence of VPA in a stoichiometric ratio of 1 :1 at room temperature with no solvent added.

13. Compound (I), according to claims 1-12, for use as a medicine.

14. Pharmaceutical composition comprising Compound (I), according to claims 1- 12, and an excipient.

15. Compound (I), according to claims 1-12, and the pharmaceutical composition according to claim 14 for use in a method of treating neurological disorders, immune disorders, or viral-related disorders.