JP2008534458A - Method for producing methylcobalamin - Google Patents

Abstract

  The present invention relates to a novel process for producing methylcobalamin comprising the methylation of cyanocobalamin or hydroxocobalamin with dimethyl carbonate in the presence of a reducing agent.

Description

The present invention is a vitamin B ₁₂ useful coenzyme types in the biosynthesis of methionine, and is widely used in agents for the management of peripheral nervous system disorders, a novel method for producing methylcobalamin (I).

  Japanese Patent Publication No. 45-38059 describes the preparation of methylcobalamin (I) by reductive methylation of cyanocobalamin (II) with methyl iodide and sodium borohydride in the presence of an iron salt to remove the resulting cyano ion. Disclosure.

  German Offenlegungsschrift 2,058,892 discloses the preparation of methylcobalamin (I) by methylation of cyanocobalamin reduced with sodium borohydride via methyl p-toluenesulfonate. This reaction occurs in the absence of oxygen and light in the presence of a metal salt (copper or iron) that results in a stable complex with the cyano ion.

German Offenlegungsschrift 2,149,150 describes methylcobalamin by methylation of hydroxocobalamin (II) with methyl mercuric iodide [MeHgI] or ammonium methylhexafluorosilicate [(NH ₄ ) SiF ₆ Me]. The preparation of (I) is disclosed.

  German Offenlegungsschrift 2,255,203 discloses methylcobalamin (III) by methylation and reduction of hydroxocobalamin (III) via methyl oxalate monoester and zinc powder in the presence of a cobalt salt that catalyzes the reaction. The preparation of I) is disclosed.

  German Patent Publication No. 2,434,967 discloses the methylcobalamin (I) by methylation and reduction of cyanocobalamin (II) via methyl oxalate and zinc powder in the presence of a cobalt salt that catalyzes the reaction. The preparation is disclosed.

  Belgian Patent No. 889,787 discloses the preparation of methylcobalamin (I) by reduction of cyanocobalamin (II) with sodium borohydride followed by methylation with methyl iodide. Is carried out in the presence of an aldehyde to sequester the released cyano ions.

  EP 1236737 discloses the preparation of methylcobalamin by reductive methylation of cyanocobalamin or hydroxocobalamin via sodium borohydride and trimethylsulfonium or trimethylsulfoxonium halide in the presence of iron or cobalt salts. is doing.

  All of these methods are not commercially available reagents (oxalic acid monoester, ammonium methyl hexafluorosilicate) or toxic reagents (methyl iodide, methyl p-toluenesulfonate) or non-environmentally compatible reagents ( (Mercury iodide) has some disadvantages.

  Methylation with trimethylsulfonium or trimethylsulfoxonium halide produces dimethylsulfur as a by-product, which is harmful and offensive. Formation of dimethyl sulfoxide as a by-product may also occur, which is not toxic but is not easily removed from the aqueous phase due to its high solubility and high boiling point (189 ° C.).

  In conclusion, industrial methods for producing methylcobalamin using non-toxic and / or environmentally compatible methylating agents are currently not available.

The present invention provides a novel method for producing methylcobalamin (I) comprising using a non-toxic and environmentally compatible reagent, dimethyl (IV) carbonate, as a methylating agent.

  In recent years, dimethyl carbonate has emerged as a methylating agent in organic chemistry, particularly in the field of so-called environmental environmental chemistry. The advantages of dimethyl carbonate are its non-toxicity, low commercial cost, and only carbon dioxide and methanol are formed as by-products.

  However, dimethyl carbonate usually requires anhydrous and harsh conditions due to its poor reactivity and insolubility in water. Processing conditions are usually in strong basic media at high temperatures.

In the present invention, dimethyl carbonate is a water-insoluble reagent (Merck Index, 13th edition, # 6065), but cobalamin Co obtained by reduction of either cyanocobalamin (II) or hydroxocobalamin (III). It has been demonstrated to be an excellent methylating agent in the ^I reduced form (B _12S ). This is why the so-called supernucleophilic B _12S anion is known to be one of the most powerful nucleophilic reagents in organic chemistry (NN Greenwood and A. Earnshaw, “Elemental Chemistry (Chemistry of the elements), Pergamon Press, Oxford, England, 1984, 1321-1322.

及び、後に、炭酸ジメチルのメチル基でＢ_１２Ｓを求核的に攻撃することでメチルコバラミンが得られる。 In fact, the aforementioned nucleophilic form Co ^I (B _12S ) is obtained from the reduction of cobalamin B ₁₂ by the following scheme (D. Autisser et al., Bull. Soc. Chim. France 1980, part 2, 192):

And later, methylcobalamin is obtained by nucleophilic attack of _B12S with the methyl group of dimethyl carbonate.

Thus, the main embodiment of the present invention is the production of methylcobalamin (I) by reducing cyanocobalamin (II) or hydroxocobalamin (III) and subsequently methylating with dimethyl (IV) carbonate:

  Thus, since the effect of the present invention is based on the preparation of methylcobalamin with dimethyl carbonate under mild, non-anhydrous conditions, this indicates that the reaction is carried out under very selected conditions. Is possible.

  In fact, the methylation reaction takes place in an aqueous medium in the presence of the reducing agent (V), with or without an organic cosolvent, in a slightly basic medium at about ambient temperature.

  Under these conditions, methylcobalamin is obtained with good yield and quality. Furthermore, methylation with dimethyl carbonate does not form by-products that can cause safety, toxicity or environmental problems.

  The amount of dimethyl carbonate to be used can vary from 1 to 25 equivalents, but is preferably 3 to 15 equivalents.

  As the reducing agent (V), those capable of reducing Co (III) atoms to Co (I), in particular halides, and more particularly sodium borohydride, can be used.

  The amount to be used of the reducing agent (V) is not critical, but 4 to 25 equivalents, preferably 10 to 20 equivalents are generally used.

  The reaction temperature can vary from 5 to 60 ° C, but a temperature of 20 to 40 ° C is recommended.

  The reaction is carried out in the presence of a sequestering agent for cyano ions under standard conditions described in the literature. The use of iron salts such as ferrous sulfate and cobalt salts such as cobalt (II) chloride is particularly efficient.

  The amount of cyanoion sequestering agent to be used is small, usually in the range between 0.1 and 1.0 equivalents, preferably between 0.2 and 0.5 equivalents.

  The reaction can be carried out by adding each solution of reducing agent and dimethyl carbonate sequentially or simultaneously under the conditions described above.

The reaction is carried out in an aqueous or aqueous-organic medium. If an organic solvent is used, its polarity should be sufficient to obtain solubilization in an aqueous reaction medium. For example, alcohols, ketones, ethers, esters, nitriles, amides and ureas, preferably alcohols and lower ketones are useful. Preferred solvents are methanol, ethanol, n- propanol, C ₁ -C ₄ alcohols, such as i- propanol; acetonitrile and dimethylformamide; ketones such as acetone and methyl ethyl ketone; tetrahydrofuran and ethers, such as dioxane.

  The reaction is carried out in the absence of oxygen and light to avoid the photo-oxidative degradation of methylcobalamin (RJ Anderson et al., Journal of Organic Chemistry 1992, 437, 227-337).

  The invention will now be described in detail by the following non-limiting examples.

Example 1 Methylcobalamin (I)
In an inert atmosphere and red light, 10 g (0.0074 mol) cyanocobalamin, 0.65 g (0.0027 mol) cobalt (II) chloride hexahydrate, 6.65 g (0.075 mol) dimethyl carbonate in 125 ml water. Mol) was added to a stirred solution of 4.2 g (0.11 mol) of sodium borohydride and 0.42 g of 1N sodium hydroxide in 25 ml of water at 35-40 ° C. over 2 hours. After stirring for 4 hours at the same temperature, the mixture was allowed to cool at 10 ° C., stirred for a further 3 hours and then filtered. The resulting solid was treated with 200 ml of acetone / water (60:40 v / v) and filtered. The resulting solution was concentrated under reduced pressure until acetone was removed. This aqueous solution was chromatographed through 500 ml of nonpolar resin (Amberlite XAD-2). All inorganic salts were removed by first washing with water until constant conductivity, and then methylcobalamin was eluted with a methanol / water (50/50 v / v) mixture. The eluate containing the pure product was concentrated under reduced pressure and then precipitated with 10 volumes of acetone to give 8.4 g (85%).
UV spectrum, pH 2.0 solution: maximum absorption at 262-266, 303-307 and 459-463 nm.
UV spectrum, pH 7.0 solution: maximum absorption at 265-269, 340-344 and 520-524 nm.
The purity by chromatographic evaluation (HPLC) was> 99%.

(Example 2) Methylcobalamin (I)
To a solution of 13 g (0.0096 mol) of cyanocobalamin, 0.91 g (0.0038 mol) of cobalt (II) chloride hexahydrate in 169 ml of water was added. The mixture was heated at 35-37 ° C., protected from light under a nitrogen atmosphere, a solution of 4.75 g (0.053 mol) of dimethyl carbonate in 13 ml of methyl ethyl ketone, and 26 ml of water containing 0.26 ml of 2N sodium hydroxide. A solution of 5.2 g (0.138 mol) of sodium borohydride in was added simultaneously over 3 hours. After stirring for 1 hour at 35-37 ° C., the mixture was allowed to cool at 12 ° C., stirred for an additional 3 hours and filtered. The resulting solid was treated with 182 ml of acetone / water (50:50 v / v) at 35-40 ° C. and filtered. The resulting solution was concentrated under reduced pressure until acetone was removed. This aqueous solution was chromatographed through 500 ml of non-polar resin (Diaion HP20L). All inorganic salts were removed by first washing with water until constant conductivity, then the methylcobalamin was eluted with a methanol / water (50/50 v / v) mixture. Fractions containing pure product were concentrated under reduced pressure and then precipitated with 10 volumes of acetone to give 11.6 g (90%).

Claims (5)

  A process for producing methylcobalamin comprising methylation of cyanocobalamin or hydroxocobalamin with dimethyl carbonate in the presence of a reducing agent.   The process of claim 1, wherein the methylation occurs in an aqueous or water-organic medium in the presence of a sequestering agent of cyano ions.   The method according to claim 1 or 2, wherein the reducing agent is sodium borohydride.   The method according to any one of claims 1 to 3, wherein the sequestering agent is iron (II) sulfate or cobalt (II) chloride.   5. A process according to any one of claims 1 to 4 wherein the reaction occurs by adding sodium borohydride and dimethyl carbonate sequentially or simultaneously.