Method for production of dimeric alkaloids

Abstract: A method for producing a dimeric alkaloid which comprises reacting catharanthine with vindoline in the presence of Fe³⁺, and either removing or inactivating the Fe³⁺ and reacting the reaction product with a reducing agent or adding oxygen and a dicarboxylic acid or a derivative thereof to the reaction system and reacting the reaction product with a hydride source. By this method such dimeric alkaloids as vinblastine, leurocidin and 3′,4′-anhydrovinblastine, which are useful as antineoplastic drugs, can be produced in high yields.

Description: This invention relates to an improved method for producing in high yields such dimeric alkaloids as vinblastine and leucocidin, which are useful as antineoplastic drugs. Such dimeric alkaloids as vinblastine and 3',4'-anhydrovinblastine are known to possess antineoplastic activity (US-A-4,029,663). These compounds can be obtained by extraction from a plant of genus Catharanthus, having the scientific name of Catharanthus roseous (alias Vinca rosea), or by methods which resort to chemical synthesis using catharanthine and vindoline derived from the plant as starting materials. Extraction methods entail difficulties in separation and purification of the dimeric alkaloids because the plant contains very little dimeric alkaloid and also because a number of analogous compounds are also present in the plant. Among the methods resorting to chemical synthesis is a method which comprises oxidizing catharanthine with a peracid, acylating the resultant N-oxide, causing reaction of the acylated product with vindoline and reducing the reaction product with NaBH₄ (US-A-4,144,237). This method, however, attains isolation of 3',4'-anhydrovinblastine only in a low yield of 41% and simultaneously gives rise to 10% of isomers as a by-product. Thus, this method entails difficulties in separation and purification of the dimeric alkaloids. WO-A-88/02002 describes the preparation of alkaloid dimers by coupling vindoline and catharanthine in the presence of ferric ion. Mindful of the commercialized production of dimeric alkaloids we have found a special interest in the method which comprises coupling of catharanthine with vindoline in the presence of Fe³⁺ and then causing the product of coupling to react with a reducing agent or a hydride source. We have tried the reaction of the product of coupling with various reducing agents or hydride sources, to find that this method is not particularly effective in improving the yield of the dimeric alkaloids. We have continued a study with a view to improving the yield of the dimeric alkaloids and have found a method whereby the yield of vinblastine, which has utility as a cancer depressant, can be greatly improved. The invention accordingly provides a method for producing a dimeric alkaloid, which comprises reacting catharanthine with vindoline in the presence of Fe³⁺, adding oxygen and a dicarboxylic acid or derivative thereof to the reaction system and reacting the reaction product with a hydride source. Preferably the dicarboxylic acid is oxalic acid, malonic acid, or a 2-position substituted malonic acid and the dimeric alkaloid is vinblastine or leurosidine. In the method of this invention, the reaction of catharanthine with vindoline in the presence of Fe³⁺ can be carried out as conventionally practiced. Although this reaction can be carried out in the air, better results are achieved when it is carried out in an atmosphere of nitrogen or under a current of nitrogen until the addition of a dicarboxylic acid or derivative thereof. After the addition of the dicarboxylate, the reaction is continued in an atmosphere of air, under a current of air, in an atmosphere of oxygen, or under a current of oxygen. The addition of the dicarboxylate is then followed by the addition of a hydride source. Hydride sources which are usable in this method include sodium borohydride, potassium borohydride, sodium cyanoborohydride amine complexes of borane, for example. Desirably, such a hydride source is added in an amount of 0.05 to 10 mol, preferably 0.1 to 1 mol, per mol of Fe³⁺. The dicarboxylic acids which are usable herein include aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, aromatic dicarboxylic acids, and heterocyclic dicarboxylic acids, for example. They may be used either singly or as mixtures. In this invention, these dicarboxylic acids can be extensively used without reference to discrimination between saturation and unsaturation. As examples of these dicarboxylic acids, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, maleic acid, fumaric acid, phthalic acid, isophthalic acid, terephthalic acid, and derivatives of such acids may be mentioned. Among other dicarboxylic acids mentioned above, saturated aliphatic dicarboxylic acids are usable particularly advantageously. The saturated aliphatic dicarboxylic acids which can be used include oxalic acid and malonic acid and such 2-position-substituted malonic acids as 2-hydroxymalonic acid, 2-methylmalonic acid, 2-ethylmalonic acid, 2,2-dimethylmalonic acid, 2-aminomalonic acid, 2-nitromalonic acid, 2,2-dihydroxymalonic acid, 2-phenylmalonic acid, and 2-benzylmalonic acid, for example. Besides the free acids mentioned above, salts, amides, and other derivatives of such acids are similarly usable for the present reaction. The bases which are usable for the formation of such salts include such alkali metals as sodium, potassium and lithium, and amines such as ammonia, methylamine, dimethylamine, trimethylamine and ethylamine, for example. Such quaternary ammonium salts as tetramethyl ammonium, tetraethyl ammonium, tetrapropyl ammonium, tetrabutyl ammonium, and trimethylbenzyl ammonium are similarly usable. Ammonium oxalate, methyl ammonium oxalate, potassium oxalate, ammonium malonate, and potassium malonate are preferably used. The salt of dicarboxylic acid to be added is suitably used in an amount of 1 to 10 mol, preferably 1 to 4 mol, per mol of Fe³⁺. Solvents which are usable in this reaction include ketones such as acetone and methylethyl ketone, tetrahydrofuran, alcohols such as methanol and ethanol, acetonitrile, DMF, DMSO, and water, for example. Optionally, a mixture of such solvents may be used. Desirably, water alone or a mixed solvent of water and methanol may be used. The reaction can be carried out at a temperature between above the melting point of the reaction solvent and 50°C. Desirably, this reaction temperature is from -10° to 10°C. The dimeric alkaloid which is formed by this reaction can be obtained by basifying the reaction system containing the product by treatment with the hydroxide of an alkali metal, a (bi)carbonate, urea, ammonia, or an amine and then extracting the dimeric alkaloid with an organic solvent. Since this method produces various species of dimers, such dimers may be separated from one another. These dimers in the mixed state manifest an antineoplastic activity and therefore they may be utilized in the mixed state. In this case, they can be expected to manifest various physiological activities other than the antineoplastic activity. By this method, dimeric alkaloids such as vinblastine and leurosidine are formed in increased yields and vinblastine is formed in a remarkable high yield. The invention will now be described with reference to Examples. Example 1: In a reaction vessel having an inner volume of 50 ml, 10 ml of water was placed, kept cooled with ice and, at the same time, bubbled with nitrogen for 30 minutes. To this water, 200 µl (2.39 µ mols) of an aqueous 11.9 mM catharanthine half-sulfate, 200 µl (2.41 µ mols) of 12.0 mM vindoline hydrochloride solution, and 1.0 ml (1.20 m mol) of an aqueous 1.2 M ferric chloride solution were added sequentially in the order mentioned. The resultant mixture was kept cooled with ice and bubbled with nitrogen and, at the same time, stirred for three hours. Then, the resultant mixture and 0.51 g (3.6 m.mols) of ammonium oxalate added thereto were bubbled with air and kept cooled with ice and, at the same time, stirred for 30 minutes. After 30 minutes following the completion of the stirring, the resultant reaction mixture was stirred in conjunction with 1 ml (227 µ mol) of an aqueous 227 mM NaBH₄ solution for 30 minutes. Thereafter, the resultant reaction mixture was alkalinized by addition of 2.00 ml of 25% aqueous ammonia and extracted three times each time with 10 ml of ethyl acetate. The extract consequently collected was dried under a vacuum at a temperature of not higher than 40°C and analyzed by HPLC under the following conditions. As the result, vinblastine and leurosidine were obtained in respective yields of 30% and 11%. Column: YMC-packed column, Am-312 (S-5 120A ODS). Solvent: A 3 : 2 mixture of CH₃CN : Aqueous 0.01 M ammonium carbonate solution. Flow rate: 1 ml/min. Column temperature: 45° Detection wavelength: 254 nm Retention time: Leurosidine (10.8 to 15 minutes: variable with the time of use of the column), vinblastine (12.5 minutes), and 3',4'-anhydrovinblastine (40.8 minutes) Example 2: Vinblastine and leurosidine were obtained in the respective yields of 27% and 12% by following the procedure of Example 1, except ammonium malonate was added in place of ammonium oxalate. Example 3: Vinblastine and leurosidine were obtained in the respective yields of 32% and 11% by following the procedures of Example 1, except methyl ammonium oxalate was added in place of ammonium oxalate. Example 4: Vinblastine and leurosidine were obtained in the respective yields of 28% and 19% by following the procedure of Example 1, except tetramethyl ammonium oxalate was added in place of ammonium oxalate. Example 5: Vinblastine and leurosidine were obtained in the respective yields of 28% and 20% by following the procedure of Example 1, except potassium oxalate was added in place of ammonium oxalate. Example 6: Vinblastine and leurosidine were obtained in the respective yields of 27% and 14% by following the procedure of Example 1, except ammonium 2-methylmalonate was added in place of ammonium oxalate. As demonstrated by Examples 1 to 6, this invention allows an improvement of more than 10% in the yields of vinblastine as compared with the conventional method which contemplates no addition of a dicarboxylic acid or derivative thereof to the reaction system. In light of the very high price of vinblastine as a medicine, this improvement in yield promises a great economic contribution.

Claims: A method for producing a dimeric alkaloid, which comprises reacting catharanthine with vindoline in the presence of Fe³⁺, adding oxygen and a dicarboxylic acid or derivative thereof to the reaction system and reacting the reaction product with a hydride source. A method according to claim 1, wherein said dicarboxylic acid is oxalic acid, malonic acid or a 2-position substituted malonic acid and said dimeric alkaloid is vinblastine or leurosidine.

Inventors: HATA EIICHIROU MITSUI PETROCHE, ISHITOKU TAKESHI MITSUI PETROC, KIHARA NORIAKI MITSUI PETROCHE, SAKAMOTO NAOYA MITSUI PETROCHE, TAN HIROAKI MITSUI PETROCHEMIC, HATA, EIICHIROU MITSUI PETROCHEMICAL IND., LTD., ISHITOKU, TAKESHI MITSUI PETROCHEMICAL IND., LTD., KIHARA, NORIAKI MITSUI PETROCHEMICAL IND., LTD., SAKAMOTO, NAOYA MITSUI PETROCHEMICAL IND., LTD., TAN, HIROAKI MITSUI PETROCHEMICAL INDUSTRIES, LTD.
Applicants: MITSUI PETROCHEMICAL IND, MITSUI PETROCHEMICAL INDUSTRIES, LTD.
Application year: 1989
Main classification: C07D519
IPC codes: C07D519