PROCESS FOR THE PREPARATION OF STABLE, NON-HYGROSCOPIC SALTS OF L(-)CARNITINE AND ALKANOYL L(-)CARNITINES

Abstract: Stable, non-hygroscopic salts of L(-)carnitine and alkanoyl L(-)carnitines with mucic acid of formula (I) are disclosed wherein the molar ratio between the carnitine moiety and mucic acid is 2:1. A process for producing the salts and solid orally administrable compositions containing same are also disclosed.

Description: PROCESS FOR THE PREPARATION OF STABLE . NON-HYGROSCOPIC SALTS OF L(-.CARNITINE AND ALKANOYL T, ( - 1CARNITINES . The present invention relates to an improved process for preparing stable, non-hygroscopic salts of L(-)carnitine and al anoyl L(- )carnitines . These salts lend themselves to the preparation of solid pharmaceutical compositions suitable for oral administration, such as pills, tablets, chewable tablets, capsules, granulates, powders and the like, of which L( - )carnitine or the alkanoyl L( - )carnitines , optionally formulated with the usual pharmacologically acceptable excipients, constitute the active ingredient. These stable, non-hygroscopic salts also facilitate the production of solid compositions which may contain other active ingredients, e.g. with a nutritional and/or dietetic effect. These compositions which are administered orally constitute by far the most preferable administration form for a vast range of users and are increasingly establishing themselves on the so- called health food, medical food or neutraceutical market. These terms, which have yet to be rigourously defined from the regulatory point of view, denote foods or food components such as food supplements, dietetic products, energy foods, and the like, i.e. formulations which are not addressed to mainly or exclusively therapeutic purposes but which are aimed rather at enhancing well-being and at producing a general improvement in fitness and performance on the part of the consumer or at preventing metabolic disorders caused by dietary deficiencies or by the inadequate biosynthesis of essential endogenous substances as a result of advancing age. The growing interest in L( - )carnitine and its derivatives in this field, too, stems from the increasingly widespread recognition, corroborated by scientific evidence, that L(- )carnitine and the lower alkanoyl L(- )carnitines , in addition to their well-known therapeutic value in the treatment of various diseases, make a marked contribution towards supplying energy to the skeletal musculature and increasing the resistance to prolonged, intense stress in professional athletes or in any subject practising sport also at amateur level, enhancing the performance capability of such subjects. In addition, L( - )carnitine or its lower alkanoyl derivatives constitute indispensable nutritional supplements for vegetarians, whose diets have a low carnitine content as well as a low content of the two amino acids, lysine and methionine, which are the precursors of the biosynthesis of L(- )carnitine in the kidneys and liver. The same considerations apply not only to those subjects who have to live on a diet poor in protein for prolonged periods of time, but, in general, also to those subjects who, though not presenting any clearly definable pathological condition, feel debilitated, experiencing a particular state of stress or physical and/or mental fatigue. All these applications indicate that the solid orally administrable compositions are the preferred presentation form, inasmuch as they make it particularly easy for users to take the substances and comply with optimal dosage regimens. Of growing interest, moreover, is the use of L(- )carnitine and its derivatives in the veterinary field and as animal feed supplements in the breeding of livestock, some species of fish, and, most notably, valuable animals such as racehorses and thoroughbreds. It has long since been known that L ( - )carnitine and its alkanoyl derivatives are extremely hygroscopic and not very stable when they occur as inner salts (or "betaines" ) as represented by the formula + ^ ^^- coo ' wherein R=H or C^-C^ lower alkanoyl. This leads to complex problems of processing, stability and storage both of the raw materials and of the finished products. For example, L(- )carnitine tablets have to be packaged in blisters to keep them out of contact with the air, since, otherwise, even in the presence of normal humidity conditions, they would undergo alterations, swelling up and becoming pasty and sticky. In addition, owing to the inadequate stability, traces of trimethylamine are released which give the products an unpleasant fishy odour. It is also known that the salts of L( - )carnitine and its alkanoyl derivatives present the same therapeutic, nutritional or dietetic activities, respectively, as the so-called inner salt (or "betaines") and can, therefore, be used in their place, provided these salts are "pharmacologically acceptable", i.e. they do not present unwanted toxic or side effects. In practice, then, the choice between an "inner salt" and a true L( - )carnitine or alkanoyl L( - )carnitine salt will depend essentially on pharmacy considerations rather than on therapeutic, nutritional or dietetic considerations . The pharmaceutical technologist is indeed interested in having at his disposal salts of L(- )carnitine and its derivatives which, unlike the inner salts, are solid and stable, particularly even in conditions of prolonged storage, which are non- hygroscopic and therefore can be easily processed and formulated with the usual excipients, using blending, tabletting devices, etc., of a traditional type, and which, in addition, pose no packaging problems when converted into finished products. These salts, both in the form of raw materials and when formulated in finished products, should not, even in non-ideal storage conditions, release traces of trimethylamine which would have a repulsive effect on the user. There is now an extensive body of literature, particularly patents, disclosing the production of stable, non-hygroscopic salts of L(- )carnitine and its derivatives . Japanese patent No. 303067 (Tanabe Seiyaku), published on 19.6.1962, publication No. 5199/19, discloses a process for the preparation of carnitine orotate, teaching that it is "advantageously less hygroscopic than carnitine and its typical salt, i.e. carnitine chloride, and can therefore be easily processed" . US patent 4,602,039 (Sigma-Tau) granted on 22.7.1986 discloses acid maleate and acid fumarate of L(- )carnitine . French patent application No. 82 11626 (Sanofi) published on 6.1.1984 publication No. 2 529 545, discloses L(- )carnitine acid sulphate and acid oxalate as non-hygroscopic salts. Finally, EP 0434088 (LONZA) discloses the use of the non-hygroscopic L( - )carnitine L( + )tartrate (2:1) (the preparation and physico-chemical characterization of which were however described by D. Mϋller and E. Strack in Hoppe Seyler's Z. Physiol. Chem. 353. 618- 622, April 1972) for the preparation of solid forms suitable for oral administration, such as tablets, capsules, powders or granulates. The known processes described in the aforesaid patents entail the use of large volumes of water or hydroalcoholic mixtures or organic solvents (such as methanol, ethanol, isobutanol) wherein L(- )carnitine inner salt and/or the suitable acid [e.g. L(+) tartaric or fumaric acid] are dissolved for carrying out the salification and the subsequent crystallization. For instance, according to the previously cited EP 0434088, a boiling solution of L(+)tartaric acid in aqueous 90% ethanol is prepared and L( - )carnitine inner salt is then added thereto. This makes it necessary to concentrate large volumes of the carnitine salt-containing solution at high temperatures (50-60 C) under reduced pressure (about 200 Torr ) , with attendant noticeable energy waste. Moreover, the use of organic solvents entail high costs and serious problems of solvent recycling, environmental pollution and disposal of toxic waste materials . The process of the present invention for preparing a stable, non-hygroscopic salt of L( - )-carnitine or alkanoyl L( - )-carnitine wherein the alkanoyl is a straight or branched group having 2-5 carbon atoms, of formula (I) • X ,n" • m H2O CD wherein R is hydrogen or lower, straight or branched alkanoyl group having 2-5 carbon atoms; n is 1 or 2; X n~ is the monoanion or dianion of a pharmacologically acceptable organic dicarboxylic acid H + X n~ apt to form stable and non-hygroscopic salts with L(-)- carnitine or the alkanoyl L(- )-carnitine; and m is 0; 0.5; 1; 1.5 or 2, comprises : (a) mixing at room temperature L( - )carnitine inner salt or an alkanoyl L( - )carnitine inner salt wherein the alkanoyl is as previously defined with the least amount of water necessary to obtain a slurry of pasty or semiliquid consistency; (b) adding to the slurry at room temperature an equi olar amount of the organic acid H + n X n~ with respect to L( - )carnitine or the aforesaid alkanoyl L( - )carnitine inner salt in case of a 1:1 salt or one-half of the molar amount in case of a 2:1 salt and thoroughly blending the resulting reaction mixture ; (c) carrying out the solidification/dehydration of the reaction mixture by allowing the reaction mixture to stand in the open air at relative humidity not higher than 50% or accelerating the solidification/dehydration thereof by drying means; and (d) optionally grinding the solidified reaction mixture to provide the salt as a granulate or powder product. In carrying out step (c), if it is preferred to accelerate the solidification/dehydration of the reaction mixture obtained in step (b), instead of allowing the reaction mixture to stand, a stream of air at a temperature slightly higher than room temperature and low relative humidity can be conveyed over the mixture or the mixture can be fed into a continuous drier or batch drier such as a turbotray drier, direct- heat rotary drier, drum drier, belt drier, spray drier, fluid bed drier and similar industrial driers well known to those skilled in chemical technology (see. e.g. "Drying" in Kirk-Othmer ' s Encyclopedia of Chemical Technology, vol. 8, pages 91-112, 1979). Alternatively or in combination with the aforesaid operation, the solidification of the reaction mixture can be carried out by treating it with a very small volume of a non-toxic volatile, water-miscible solvent wherein the L( - )carnitine and alkanoyl L( - )carnitine salts are insoluble, such as e.g. acetone. The process of the present invention is particularly suited for the preparation of the salts of formula (I) wherein, if R is alkanoyl, this is selected from the group comprising acetyl, propionyl, butyryl, valeryl and isovaleryl. The organic acid H + n X n~ is preferably selected from the group comprising L( + ) -tartaric, fu aric, mucic and D-glucaric acid. Among the salts of formula (I), particularly preferred for preparation via the process of the present invention are: L ( - )-carnitine L ( + )-tartrate (2:1), L(-)- carnitine acid fumarate (1:1), L( - )-carnitine mucate (2:1)«H 2 0, acetyl L( - )-carnitine mucate (2:1)«2H 2 0, propionyl L(- )-carnitine mucate (2:1)-2H 2 0, valeryl (L- )-carnitine mucate (2:1)«2H 2 0 and isovaleryl L(-)- carnitine mucate (2:1) -2^0. The following non-limiting examples show the preparation of some salts of L( - )carnitine and alkanoyl L(- )carnitines according to the process of the present invention. Example 1 : L(-)carnitine mucate (2:1) -H 2 0 (l.a) 161.2 g (1.0 mole) of L(- )carnitine inner salt and 30 mL of distilled water were mixed in a mortar to obtain a semiliquid slurry. 105.1 g (0.5 moles) of mucic acid were added to the slurry and the resulting mixture was thoroughly blended with a pestle. Upon homogenization, a semitransparent , sticky and whitish "cream" formed which could be evenly spread on the bottom and walls of the mortar. In order to accelerate the solidification of the mucate thus formed the product was exposed to the air stream of a fan (air relative humidity about 40-45%, room temperature about 22 Q C). After 15-20 minutes, the solidified L(-)carnitine mucate could be ground to the wanted particle size. By repeating the aforesaid preparation several times, it was consistently found that the water content of the end product [L(-)carnitine mucate (2:1)-2H 2 0] was 2.7-2.9% by weight. Yield: 100% It was also shown that L(- )carnitine mucate solidification and water removal till a groundable product was obtained, occurred also spontaneously after some hours by simply allowing the product to stand, i.e. without exposing the product to any air stream, (l.b) Alternatively, the slurry of L( - )carnitine and mucic acid was homogenized with a spatula on a glass plate instead of mixing the slurry with a pestle in a mortar. The resulting mucate was spread on the glass plate to form a thin layer in order to promote the spontaneous water removal. The result was similar to that previously described; however, water removal occurred in a shorter time. L( - )carnitine content, calculated on the anhydrous product, is 60.5% and 58.6% on the hydrated product. Example 2 : L(-) carnitine mucate (2:1) -H 0 16.2 g (0.1 moles) of ( - )carnitine inner salt and 3 mL of distilled water were mixed in a mortar to obtain a se iliquid slurry. 10.5 g (0.05 moles) of mucic acid were added to the slurry and the resulting mixture was thoroughly homogenized with a pestle until a se itransparent , sticky and withish "cream" formed . When the "cream" started to solidify, 70 L of acetone were added thereto while mixing with the pestle was continued. Shortly thereafter the mucate was obtained as a finely powder-like solid which was filtered off, allowed to stand at room temperature and about 50% relative humidity for 24 hours and then homogenized by trituration and/or passing it through a 200μ sieve. Yield: higher than 99%. Example 3 : Acetyl L( - ) carnitine mucate ( 2 : 1 ) • 2H 2 0 203.2 g (1.0 mole) of acetyl L( - )carnitine inner salt and 35 mL of distilled water were mixed in a mortar to obtain a semiliquid slurry. 105.1 g (0.5 moles) of mucic acid were then added to the slurry. The same procedure as that of Example 1 was then followed. The reaction mixture behaviour was the same as that of Example 1. By repeating this preparation several times, it was consistently found that the water content of the end product [acetyl L( - )carnitine mucate (2:1)-2H 2 0] was 5.5-6.0% by weight. Yield: 100%. The content of acetyl L( - )carnitine , calculated on the anhydrous product, is 65.9% and 62.3% on the dihydrate. Example 4: Propionyl L( - )carnitine mucate (2:1) • 2H 2 0 217.2 g (1.0 mole) of propionyl L( - )carnitine inner salt and 35 L of distilled water were mixed in a mortar to obtain a semiliquid slurry. 105.1 g (0.5 moles) of mucic acid were then added to the slurry. The same procedure as that of Example 1 was then followed. The reaction mixture behaviour was the same as that of Example 1. By repeating this preparation several times, it was consistently found that the water content of the end product [propionyl L(- )carnitine mucate (2:1)] was 5.4- 5.9% by weight. Yield: 100%. The content of propionyl L(- )carnitine, calculated on the anhydrous product, is 67.4% and 63.8% on the dihydrate . Example 5: Isovaleryl L(-)carnitine mucate (2:1)-2H 0 245.2 g (1.0 mole) of isovaleryl L( - )carnitine inner salt and 38 mL of distilled water were mixed in a mortar to obtain a semiliquid slurry. 105.1 g (0.5 moles) of mucic acid were then added to the slurry. The same procedure as that of Example 1 was then followed. The reaction mixture behaviour was the same as that of Example 1. By repeating this preparation several times, it was consistently found that the water content of the end product [isovaleryl L ( - )carnitine mucate (2:1)*2H 0] was 4.9-5.5% by weight. Yield: 100%. The content of isovaleryl L( - )carnitine , calculated on the anhydrous product, is 70.0% and 66.6% on the dihydrate. Example 6: L(- ) -carnitine L(+ )-tartrate (2:1) 8.05 g (0.05 moles) of L( - )-carnitine and 1.5 mL of distilled water were mixed in a mortar giving a semiliquid slurry. 3.75 g (0.025 moles) of L( + )-tartaric acid were added to the slurry and the resulting mixture was thoroughly blended with a pestle, obtaining almost immediately a homogeneous, semitransparent , colourless "cream" . The solidification time of the tartrate was longer than that of the mucate, but the times became comparable to each other when an air stream at relative humidity of ten units lower than that used for mucate solidification was blown on the sample. By treating the tartrate with an organic solvent, e.g. acetone, its final water content was lower than 1% by weight. The L(- )-carnitine content, calculated on the anhydrous product, was 68.2%. Example 7 : L(-)-carnitine fumarate (1:1) 8.05 g (0.05 moles) of L ( - )-carnitine and 1.5 mL of distilled water were mixed in a mortar giving a semiliquid slurry. 5.80 g (0.05 moles) of fumaric acid were added to the slurry and the resulting mixture was thoroughly blended with a pestle, yielding almost immediately a homogeneous, semitransparent, colourless "cream" which solidified after some time. The product treated as in the previous example showed a final water content < 1% by weight. The L( - )-carnitine content, calculated on the anhydrous product, was 58.1% by weight. It will be apparent that the moisture content of the end product depends on many factors such as the moisture content of the starting L(- )carnitine or alkanoyl L ( - )carnitine , the temperature and relative humidity of the air in the plant where the production operations are carried out, the overall processing duration and the particle size of the final product. Following exposure to relative humidity higher than 60%, in addition to crystallization water (if any), also imbibition water can be found. It will also be apparent that the present process presents several, noticeable advantages over the prior art processes: a) the process is carried out at room temperature and ambient pressure; b) no organic solvents (or very small amounts thereof) are used, thus environmental pollution is avoided; c) the yield is practically quantitative; d) starting from anhydrous L( - )carnitine or alkanoyl L(- )carnitine inner salt is not required: it is sufficient that their initial moisture content is known; e) the consistency of the starting mixture can be varied, from a semisolid slurry to dense slurries of varying flowability, by simply regulating the added amount of water (10% to 30% by weight of the whole slurry). This allows a selection among the dehydration procedures to be made: from spontaneous water evaporation to procedures which entail the use of the aforesaid industrial driers; and f) in spontaneous evaporation, the dehydration time can be shortened by placing the product in an environment of low relative humidity (e.g. 30-40%) and/or by conveying on the product a stream of air of low relative humidity, at room temperature or slightly higher.

Claims: CLAIMS 1. A process for preparing a stable, non-hygroscopic salt of L(- )-carnitine or alkanoyl L( - )-carnitine wherein the alkanoyl is a straight or branched group having 2-5 carbon atoms, of formula (I) + ( C_H 3 ) 3NCH 2 CHCH2CCOH ,χ n -. m H 2 0 OR n (I) wherein R is hydrogen or lower, straight or branched alkanoyl having 2-5 carbon atoms. n is 1 or 2; X n is the monoanion or dianion of a pharmacologically acceptable organic dicarboxylic acid H + n X n~ apt to form stable and non-hygroscopic salts with L(-)- carnitine or the alkanoyl L(- )-carnitine ; and m is 0; 0.5; 1; 1.5 or 2 , which comprises: (a) mixing at room temperature L( - )carnitine inner salt or an alkanoyl L(- )carnitine inner salt wherein the alkanoyl is as previously defined with the least amount of water necessary to obtain a pasty or semiliquid slurry; (b) adding to the slurry at room temperature an equimolar amount of the organic acid H ~ X n_ with respect to L( - )-carnitine or the aforesaid alkanoyl L( - )carnitine inner salts in case of a 1:1 salt or one-half of the molar amount in case of a 2:1 salt and thoroughly blending the resulting reaction mixture ; (c) carrying out the solidification/dehydration of the reaction mixture by allowing the reaction mixture to stand in the open air at relative humidity not higher than 50% or accelerating the solidification/dehydration thereof by drying means; and (d) optionally grinding the solidified reaction mixture to provide the salt as a granulate or powder product. 2. The process of claim 1, wherein the drying means are selected from a continuous drier, a batch drier, a turbotray drier, a direct-heat rotary drier, a drum drier, a belt drier, a spray drier and a fluid-bed drier. 3. The process of claim 1, wherein the alkanoyl is selected from the group comprising acetyl, propionyl, butyryl , valeryl and isovaleryl. 4. The process of anyone of the preceding claims wherein the organic acid H + X n~ is selected from the group comprising L ( + )-tartaric acid, fumaric acid, mucic acid and D-glucaric acid. 5. The process of anyone of the preceding claims for obtaining L( - )-carnitine tartrate (2:1), L( - )-carnitine acid fumarate (1:1), L ( - )-carnitine mucate (2:1) Η 2 0, acetyl L ( - )-carnitine mucate (2:1) « 2H 2 0, propionyl L(-)- carnitine mucate (2:1)-2H 2 0, valeryl L( - )-carnitine mucate (2:1)«2H 2 0, and isovaleryl L( -) carnitine mucate (2:1) -2H 2 0. 6. Salts of L( - )-carnitine or alkanoyl L( - )-carnitine wherein the alkanoyl is a straight or branched group having 2-5 carbon atoms, of formula (I) ( CH 3 ) 3 NCH 2 CHCH2 co OH X ,n" • m H2O j OR n CD wherein R is hydrogen or lower, straight or branched alkanoyl group having 2-5 carbon atoms; n is 1 or 2; X n~ is the monoanion or dianion of a pharmacologically acceptable organic dicarboxylic acid H + n X n~ apt to form stable and non-hygroscopic salts with L(-)- carnitine or the alkanoyl L( - )-carnitine; and is 0.5; 1; 1.5 or 2. 7. A salt according to claim 6, selected from the group consisting of L( - )carnitine mucate (2:1) Η 2 0 acetyl L( - )carnitine mucate (2:1)*2H 0 - propionyl L( - )carnitine mucate (2:1)«2H 0 isovaleryl L( - )carnitine mucate (2:1)*2H 2 0.

Inventors: FASSI ALDO, FASSI, ALDO
Applicants: FASSI ALDO, FASSI, ALDO
Application year: 1998
Main classification: C07C227
IPC codes: C07C51, C07C57, C07C59, C07C227, C07C229