Patent Description:
Tetrahydrofolates are predominantly used as <NUM>-formyltetrahydrofolic acid and the salts thereof (leucovorin and levoleucovorin), as <NUM>-methyltetrahydrofolic acid and the salts thereof (Metafolin®), or as <NUM>,<NUM>-methylenetetrahydrofolic acid and the salts thereof (Modufolin®) for the treatment of megaloblastic folic acid anaemia, as an antidote for increasing the compatibility of folic acid antagonists, particularly of aminopterin and methotrexate in cancer therapy ("antifolate rescue"), for increasing the therapeutic effect of fluorinated pyrimidines and for the treatment of autoimmune diseases such as psoriasis and rheumatoid arthritis, for increasing the compatibility of certain antiparasitic for mutations, for instance trimethoprim-sulfamethoxazole, and for reducing the toxicity of dideazatetrahydrofolates in chemotherapy.

<NUM>-Methyltetrahydrofolic acid is used in particular as a drug and as a food additive, as a vitamin preparation, for the prevention of neural tube defects, for the treatment of depressive illnesses, and for influencing the homocysteine level.

<NUM>-Methyltetrahydrofolic acid and salts thereof are extremely unstable and in particular are highly susceptible to oxidation [see also <NPL>) in this respect] and are therefore difficult to produce at a level of purity which is acceptable for a pharmaceutical active ingredient or a food additive.

Various methods, such as excluding oxygen as completely as possible or the addition of antioxidants such as ascorbic acid or reduced L-glutathione, have been employed in order to overcome the instability of <NUM>-methyltetrahydrofolic acid.

<CIT> discloses amino acid and amine salts and <CIT> glucosamine and galactosamine salts of L-methylfolate.

<NPL> is reviewing the state of the art in: pharmaceutical multicomponent phase design, the intermolecular interactions in these phases, the implications of these interactions on the material properties and the pharmacokinetics in a patient.

<CIT> discloses alkaline earth salts of <NUM>-methyltetrahydrofolic acid, particularly the calcium salt, its crystallization and its use. The crystalline calcium salts of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid exist in four different crystalline modifications.

The drawback of the calcium salts of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid is that they exist in four modifications, since the process of manufacturing each of which has to be controlled very precisely. Additionally, the solubility of said calcium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid in water is relatively poor, possibly leading to a reduced bioavailability and a limitation to its applicable form of use. Also a low solubility is resulting in low time-volume yields when needing to dissolve such compound for further processing e.g. a purification by recrystallization. Additionally the crystalline salts of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid of <CIT> also are having a water of crystallization of at least one equivalent per equivalent of <NUM>-methyltetrahydrofolic acid.

New crystal forms of a pharmaceutically useful compound offer an opportunity to improve the performance profile of a pharmaceutical and/or vitamin/medical food products. It widens the reservoir of materials a formulation scientist has available for designing new dosage forms with improved characteristics.

The technical problem underlying the present invention is solved by a crystalline salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid comprising.

wherein the molar ratio of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid to the sodium is from <NUM>:<NUM> to <NUM>:<NUM> and the molar ratio of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid to the organic base is from <NUM>:<NUM> to <NUM>:<NUM>; and/or hydrates and/or solvates thereof.

Preferably, the molar ratio of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid to the sodium is from <NUM>:<NUM> to <NUM>:<NUM> and the molar ratio of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid to the organic base is from <NUM>:<NUM> to <NUM>:<NUM> and even more preferred, the molar ratio of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid to the sodium is approximately <NUM>:<NUM> and the molar ratio of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid to the organic base is approximately <NUM>:<NUM>. Preferably, the crystalline sodium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid (MTHF) comprising an organic base having a pKa value from <NUM> to <NUM> has a molar ratio of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid to sodium to organic base having a pKa value from <NUM> to <NUM> from <NUM>:<NUM>:<NUM> to <NUM>:<NUM>:<NUM> and/or hydrates and/or solvates thereof.

Preferably, the crystalline salt has a molar ratio of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid to sodium to organic base is from <NUM>:<NUM>:<NUM> to <NUM>:<NUM>:<NUM>.

Even more preferred, the crystalline salt has a molar ratio of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid to sodium to organic base of approximately <NUM>:<NUM>:<NUM>.

The solid form of the present invention possesses improved pharmacological characteristics, for example, improved bioavailability, thus offering enhanced possibilities to modulate and design improved drug products.

Additionally, only one crystalline modification of the sodium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid and organic base exists, thus, leading to an improved and accurate process of obtaining the same.

Preferably, the crystalline salt of the present invention is the sodium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid comprising <NUM>-(<NUM>-hydroxyethyl)-morpholine and has a PXRD pattern with at least one characteristic peak (expressed in 2θ ± <NUM>° 2θ (CuKα radiation)) at <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>.

Preferably, the crystalline salt of the present invention is the sodium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid comprising <NUM>-(<NUM>-hydroxyethyl)-morpholine having a PXRD pattern with at least two, even more preferred at least three, most preferred at least four, preferably at least five, more preferred at least six, even more preferred at least seven and most preferred all of the characteristic peaks (expressed in 2θ ± <NUM>° 2θ (CuKα radiation)) at <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>.

Even more preferred, the sodium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid comprising <NUM>-(<NUM>-hydroxyethyl)-morpholine has a PXRD pattern with at least one characteristic peak (expressed in 2θ ± <NUM>° 2θ (CuKα radiation)) at <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> and most preferred the sodium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid and <NUM>-(<NUM>-hydroxyethyl)-morpholine has a PXRD pattern substantially as shown in <FIG>.

Even more preferred, the sodium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid comprising <NUM>-(<NUM>-hydroxyethyl)-morpholine has a PXRD pattern with at least two, even more preferred at least three, most preferred at least four, preferably at least five, more preferred at least six, most preferred at least seven and even more preferred all of the characteristic peaks (expressed in 2θ ± <NUM>° 2θ (CuKα radiation)) at <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>.

A further aspect of the invention is the crystalline sodium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid comprising <NUM>-(<NUM>-hydroxyethyl)-morpholine having a Raman spectrum with least one characteristic peak (expressed in wavenumbers, cm-<NUM>, with an experimental uncertainty of ± <NUM>-<NUM>-<NUM>) at: <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM>-<NUM>.

Yet a further aspect of the invention is the crystalline sodium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid comprising <NUM>-(<NUM>-hydroxyethyl)-morpholine which exhibits a Raman spectrum substantially as depicted in <FIG>.

Additionally, one crystalline modification of the sodium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid and <NUM>-(<NUM>-hydroxyethyl)-morpholine exists, thus, leading to an improved and accurate process of obtaining the same.

Preferably, the crystalline salt is the sodium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid comprising <NUM>-(<NUM>-hydroxyethyl)-pyrrolidine and has a PXRD pattern with at least one characteristic peak (expressed in 2θ ± <NUM>° 2θ (CuKα radiation)) at <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>.

Preferably, the crystalline salt is the sodium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid comprising <NUM>-(<NUM>-hydroxyethyl)-pyrrolidine and has a PXRD pattern with at least two, even more preferred at least three, most preferred at least four, preferably at least five, more preferred at least six, even more preferred at least seven and most preferred all of the characteristic peaks (expressed in 2θ ± <NUM>° 2θ (CuKα radiation)) at <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>.

Preferably, the crystalline salt is the sodium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid comprising <NUM>-(<NUM>-hydroxyethyl)-pyrrolidine and has a PXRD pattern with at least two, even more preferred at least three, most preferred at least four, preferably at least five, more preferred at least six, most preferred at least seven and even more preferred all of the characteristic peaks (expressed in 2θ ± <NUM>° 2θ (CuKα radiation)) at <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>.

Preferably, the crystalline salt is the sodium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid comprising <NUM>-(<NUM>-hydroxyethyl)-pyrrolidine has a PXRD pattern substantially as shown in <FIG>.

A further aspect of the invention is the crystalline sodium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid and <NUM>-(<NUM>-hydroxyethyl)-pyrrolidine which has a Raman spectrum with least one characteristic peak (expressed in wavenumbers, cm-<NUM>, with an experimental uncertainty of ± <NUM>-<NUM>-<NUM>) at <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM>-<NUM>.

A further aspect of the invention is the crystalline sodium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid and <NUM>-(<NUM>-hydroxyethyl)-pyrrolidine which exhibits a Raman spectrum substantially as shown in <FIG>.

Additionally, one crystalline modification of the sodium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid and <NUM>-(<NUM>-hydroxyethyl)-pyrrolidine exists, thus, leading to an improved and accurate process of obtaining the same.

Preferably, the crystalline salt of the present invention is the sodium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid comprising <NUM>-dimethylaminoethanol and having a PXRD pattern with at least one characteristic peak (expressed in 2θ ± <NUM>° 2θ (CuKα radiation)) at <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>.

Even more preferred, the crystalline salt of the present invention is the sodium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid comprising <NUM>-dimethylaminoethanol and having a PXRD pattern with at least two, even more preferred at least three, most preferred at least four, preferably at least five, more preferred at least six, even more preferred at least seven and most preferred all of the characteristic peaks (expressed in 2θ ± <NUM>° 2θ (CuKα radiation)) at <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>.

Preferably, the crystalline salt is the sodium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid comprising <NUM>-dimethylaminoethanol and having a PXRD pattern with at least one characteristic peak (expressed in 2θ ± <NUM>° 2θ (CuKα radiation)) at <NUM>,<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM>.

Even more preferred, the crystalline salt is the sodium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid comprising <NUM>-dimethylaminoethanol and having a PXRD pattern with at least two, even more preferred at least three, most preferred at least four, preferably at least five, more preferred at least six, most preferred at least seven and even more preferred all of the characteristic peaks (expressed in 2θ ± <NUM>° 2θ (CuKα radiation)) at <NUM>,<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM>.

Preferably, the crystalline salt is the sodium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid <NUM>-dimethylaminoethanol having a PXRD pattern substantially as shown in <FIG>.

A further aspect of the invention is that the crystalline sodium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid and <NUM>-dimethylaminoethanol having a Raman spectrum with least one characteristic peak (expressed in wavenumbers, cm-<NUM>, with an experimental uncertainty of ± <NUM>-<NUM>-<NUM>) at: <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM>-<NUM>.

Preferably, the crystalline sodium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid and <NUM>-dimethylaminoethanol exhibits a Raman spectrum substantially as shown in <FIG>. Additionally, one crystalline modification of the sodium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid and <NUM>-dimethylaminoethanol exists, thus, leading to an improved and accurate process of obtaining the same.

Yet a further aspect of the present invention is that the crystalline sodium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid comprising <NUM>-(<NUM>-hydroxyethyl)-morpholine can readily be obtained in favorable particulate properties. The salt of this invention can be obtained in large, rod-shape particles that show excellent sedimentation and filtration properties that are useful for separation of the solid product in large scale production (<FIG>). Contrary thereto the calcium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid according to <CIT> (<FIG>, <FIG>) does not crystallize in large, rod-shaped particles, thus, leading to poorer processing properties, since such particles are difficult to handle and difficult to separate from a suspension after crystallization by filtration.

A further aspect of the present invention is a process for obtaining the crystalline sodium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid comprising an organic base having a pKa value from <NUM> to <NUM> comprising the steps of:.

Preferably, the molar ratio of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid and sodium hydroxide in step b) is in the range of from1:<NUM> to <NUM>:<NUM> and more preferred from <NUM>:<NUM> to <NUM>:<NUM>. In a further preferred embodiment, the molar ratio of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid and the organic base having a pKa value from <NUM> to <NUM> in step c) is in the range of from <NUM>:<NUM> to <NUM>:<NUM>.

Preferably, the solvent and/or mixtures of solvents according to step a), c) and/or d) is selected from the group consisting of water, water-soluble alcohols, methanol, ethanol, isopropanol, n-propanol, acetonitrile, tetrahydrofuran, acetone, methyl ethyl ketone, methyl isobutyl ketone, benzylalcohol, and mixtures thereof.

Furthermore, steps b) and c) can be interchanged.

Preferably, in step c), d) and/or e) the temperature is less than <NUM>, more preferred less than <NUM>, even more preferred less than <NUM> and most preferred less than <NUM>.

Preferably, in step a), b), c), d) and/or e) seed crystals are added. Even more preferred the seed crystals are the desired sodium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid comprising an organic base having a pKa value from <NUM> to <NUM>.

A further aspect of the present invention is a pharmaceutical composition, food additive, vitamin and/or other preparation comprising the crystalline sodium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid comprising an organic base according to the present invention and optionally one or more acceptable excipients and the use of the crystalline sodium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid and the organic base according to the present invention as constituent for the production of drugs, vitamins and/or food additives.

The crystalline sodium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid comprising an organic base of the present invention for use in the treatment of anemia, neural tube defects, cardiovascular diseases, depression, Alzheimer's disease, cognitive impairment and osteoporosis and/or dietary management of low plasma and/or low red blood cell and/or low cerebrospinal fluid and/or low peripheral or central nervous system folate is also part of the present invention.

Surprisingly, the crystalline sodium salts of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid of the present invention have an improved kinetic solubility compared with the crystalline calcium salt disclosed in <CIT>. The measurement of the kinetic solubility was conducted as described in the experimental part.

The solubility of the crystalline sodium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid comprising <NUM>-(<NUM>-hydroxyethyl)-morpholine of the present invention in water (room temperature) is greater than <NUM> per <NUM> of water, whereas the calcium salt exhibits a solubility being considerably smaller than <NUM> per <NUM> of water. [remark: not assay corrected].

Moreover, the crystalline sodium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid comprising <NUM>-(<NUM>-hydroxyethyl)-pyrrolidine also has a solubility greater than <NUM> per <NUM> of water (room temperature).

Additionally, the crystalline sodium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid comprising <NUM>-dimethylaminoethanol also has a solubility greater than <NUM> per <NUM> of water (room temperature).

Due to the higher solubility of the sodium salts of the present invention the bioavailability is much better. This results in oral dosage forms, in which the amount of the active ingredient can be reduced, without diminishing the effectivity of the medicament or food additive.

Surprisingly, each of the above described crystalline sodium salts of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid and an organic base having a pKa value from <NUM> to <NUM> of the present invention form only one crystalline form which leads compared with the calcium salts of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid disclosed in <CIT> to a sleek and accurate process of manufacturing which can be controlled very precisely. Said result could not be foreseen by the skilled artisan.

Pharmaceutical compositions according to the present invention can be applied for all modes of administration, preferably for oral, parenteral, intramuscular, intraspinal, intrathecal, periodontal, topical or rectal administration.

Light microscopy was performed on a Leitz Orthoplan polarized microscope, generally a 10x10 magnification was applied.

Thermogravimetric measurements were carried out with a Netzsch Thermo-Microbalance TG <NUM> coupled to a Bruker FTIR Spectrometer Vector <NUM> (sample pans with a pinhole, N<NUM> atmosphere, heating rate <NUM>/min).

FT-Raman spectra were recorded on a Bruker MultiRAM FT-Raman or a Bruker RFS <NUM> FT-Raman system with a near infrared Nd:YAG laser operating at <NUM> and a liquid nitrogen-cooled germanium detector. <NUM> scans with a resolution of <NUM>-<NUM> were accumulated in the range from <NUM> to -<NUM>-'; however, only data above <NUM>-<NUM> are evaluated due to filter cutoff effects. Nominal laser powers are typically <NUM> or <NUM> mW.

To <NUM> of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid monohydrate (assay <NUM>-methyltetrahydrofolic acid <NUM>%w/w) were weighed into a glass vial equipped with a magnetic stirrer bar. <NUM> of sodium hydroxide standard solution <NUM> mol/L and <NUM>µl of <NUM>-(<NUM>-hydroxy-ethyl)-morpholine were added and the mixture was sonicated to obtain an essentially clear solution. At ambient temperature, <NUM> ethanol was added followed by seeding with about three mg of crystalline monosodium salt. Then <NUM> ethanol was added and the seeding step was repeated. Upon seeding, a thick suspension was obtained that was diluted with <NUM> of an ethanol - water <NUM>:<NUM> mixture. After stirring at r. for about one hour the solid product was separated by filtration and after drying in air at r. , characterized by powder X-ray diffraction (<FIG>, Table <NUM>), <NUM>H-NMR, light microscopy and TG-FTIR. The yield was about <NUM>. The sample was further examined by HPLC, Raman spectroscopy, and IC-OES for determination of the sodium content. <NUM>H-NMR shows that when the integral for the two protons of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid near <NUM> is normalized to <NUM> the resultant integral for the six protons of the <NUM>-(<NUM>-hydroxy-ethyl)-morpholine that appear near <NUM> is <NUM>. This shows that the molar ratio of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid to <NUM>-(<NUM>-hydroxy-ethyl)-morpholine is essentially <NUM>:<NUM>. Further analysis by TG-FTIR shows a water content of about <NUM> wt-%. The sodium content was determined by ICP-OES (inductively coupled plasma atomic emission spectroscopy) and a content of <NUM> wt-% sodium was found. This shows that the molar ratio of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid to sodium is essentially <NUM>:<NUM>. The product was further investigated by Raman spectroscopy <FIG>, Table <NUM>.

<NUM> of crystalline <NUM>-methyl-(<NUM>)-tetrahydrofolic acid sodium salt containing <NUM>-(<NUM>-hydroxy-ethyl)-morpholine (according to Example <NUM>) with a stoichiometric ratio of <NUM>:<NUM>:<NUM> are weighed into a <NUM> glass vial with screw cap. <NUM> of purified/de-ionized water (for instance water for chromatography) is added. The mixture is vigorously agitated at room temperature and briefly sonicated and a clear slightly yellow solution is readily obtained (within a few seconds). Thus the solubility is greater than <NUM> per <NUM> of water. The solution remains clear for several hours at r.

<NUM> of crystalline calcium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid (containing about <NUM>% of water, thus corresponding to a dry weight of about <NUM>) are weighed into a <NUM> glass vial with screw cap. <NUM> of purified/de-ionized water (for instance water for chromatography) is added to the solid using an adjustable volumetric pipette. The mixture is vigorously agitated at room temperature and briefly sonicated. No clear solution can be obtained and a fairly concentrated suspension persists. Thus the kinetic solubility measured as described here is smaller than <NUM> per <NUM> of water.

A small aliquot (a few microliters) of the suspension obtained upon crystallization of the sodium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid comprising <NUM>-(<NUM>-hydroxyethyl)-morpholine is transferred on a microscopy glass slide and examined with a light microscope from on Leitz Orthoplan under polarized light. A 10x10 magnification was applied. Microscopy shows rod shaped particles with lengths of up to about <NUM> and a thickness of about <NUM> to <NUM>µ. Such particles are easy to handle and have favorable filtration and drying properties. An image is shown in <FIG>.

A small aliquot (a few micrograms) of crystalline calcium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid is transferred on a microscopy glass slide and examined as dry powder with a light microscope under polarized light. A 10x10 magnification was applied. Microscopy shows large agglomerates that consist of a multitude of very small particles. Such particles are difficult to handle. An image is shown in <FIG>.

To <NUM> of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid monohydrate (assay <NUM>-methyltetrahydrofolic acid <NUM>%w/w) were weighed into a glass vial equipped with a magnetic stirrer bar. <NUM> of sodium hydroxide standard solution <NUM> mol/L, then <NUM>µl of <NUM>-(<NUM>-hydroxyethyl)-pyrrolidine and <NUM> ethanol were added. The resultant mixture was sonicated and stirred at ambient temperature for two hours. A thick suspension was obtained that was diluted with <NUM> of an ethanol - water mixture <NUM>:<NUM> v/v and stirring was continued for one hour before the solid product was separated by filtration. After drying in air at ambient temperature for half an hour the product was characterized by powder X-ray diffraction (<FIG>, Table <NUM>), H-NMR, and TG-FTIR. The yield was about <NUM>. The sample was further examined by HPLC and showed an HPLC purity of <NUM> area-%. H-NMR spectroscopy shows that when the integral for the two protons of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid near <NUM> is normalized to <NUM>, the resultant integral for the four methylene protons in the five-ring near <NUM> ppm of <NUM>-(<NUM>-hydroxyethyl)-pyrrolidine is <NUM>. This suggests that the molar ratio of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid to <NUM>-(<NUM>-hydroxyethyl)-pyrrolidine is essentially <NUM>:<NUM>. Further analysis by TG-FTIR suggests a water content of about <NUM>%. The sodium content was determined by ICP-OES (inductively coupled plasma atomic emission spectroscopy) and a content of <NUM> wt-% sodium was found. This shows that the molar ratio of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid to sodium is essentially <NUM>:<NUM>. The product was further investigated by Raman spectroscopy <FIG>, Table <NUM>.

<NUM> of crystalline sodium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid comprising <NUM>-(<NUM>-hydroxyethyl)-pyrrolidine is weighed into a <NUM> glass vial with screw cap. Then <NUM> of purified/de-ionized water is added. The mixture is agitated at room temperature and a clear solution is readily obtained (within a few seconds). Thus the solubility is greater than <NUM> per <NUM> of water. The solution remains clear for several hours at r.

<NUM> of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid monohydrate (assay <NUM>-methyltetrahydrofolic acid <NUM>%w/w) were weighed into a glass vial equipped with a magnetic stirrer bar. The added <NUM> of sodium hydroxide standard solution <NUM> mol/L, then added <NUM>µl of <NUM>-dimethylaminoethanol (~<NUM> equivalents). To the essentially clear solution <NUM> of ethanol was added. The resultant mixture was sonicated, seeded with crystalline salt, and stirred at ambient temperature for one hour. A thick suspension was obtained that was diluted with <NUM> of an ethanol - water mixture <NUM>:<NUM> v/v and stirring was continued for one hour before the solid product was separated by filtration and after drying in air at r. The crystalline product was characterized by H-NMR, Raman spectroscopy, PXRD, and TG-FTIR. Powder X-ray diffraction shows that the sample is clearly crystalline in nature (<FIG>, Table <NUM>). H-NMR spectroscopy shows that when the integral for the two protons of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid near <NUM> is normalized to <NUM>, the resultant integral for the six protons of the two methyl groups <NUM>-dimethylaminoethanol near <NUM> ppm of is <NUM>. This suggests that the molar ratio of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid to <NUM>-dimethylaminoethanol is essentially <NUM>:<NUM>. The sample was further examined by Raman spectroscopy and it shows a Raman spectrum as described in Table <NUM> and shown in <FIG>. The sodium content was determined by ICP-OES (inductively coupled plasma atomic emission spectroscopy) and a content of <NUM> wt-% sodium was found. Further analysis by TG-FTIR suggests a water content of about <NUM>%. Based on the two results, the product has a <NUM>:<NUM> molar ratio of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid to sodium.

<NUM> of crystalline sodium salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid comprising <NUM>-dimethylaminoethanol is weighed into a <NUM> glass vial with screw cap. Then <NUM> of purified/de-ionized water is added. The mixture is agitated at room temperature and a clear solution is readily obtained (within a few seconds). Thus the solubility is greater than <NUM> per <NUM> of water. The solution remains clear for several hours at r.

Claim 1:
A crystalline salt of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid comprising
(i) <NUM>-methyl-(<NUM>)-tetrahydrofolic acid,
(ii) sodium and
(iii) an organic base having a pKa value from <NUM> to <NUM>, selected from the group consisting of <NUM>-(<NUM>-hydroxyethyl)-morpholine, <NUM>-(<NUM>-hydroxyethyl)-pyrrolidine, imidazole, <NUM>-dimethylaminoethanol, and tert-butylamine; and mixtures thereof; wherein the molar ratio of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid to the sodium is from <NUM>:<NUM> to <NUM>:<NUM> and the molar ratio of <NUM>-methyl-(<NUM>)-tetrahydrofolic acid to the organic base is from <NUM>:<NUM> to <NUM>:<NUM>; and/or hydrates and/or solvates thereof.