Malononitrile → Levosimendan

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U.S. Pat. No. 5,569,657 discloses the preparation of levosimendan and its salts. (±)-6-(4-aminophenyl)-5-methylpyridazin-3-(2H)-one is dissolved in 2-propanol on heating. L-tartaric acid is gradually added to the solution and stirred on heating to obtain a clear solution. The solution is cooled slowly to room temperature and then stirred overnight at 200 C to obtain a crystalline product. On filtering, the wet salt is dissolved in water and to it potassium carbonate solution is added with stirring. The free base obtained is filtered, washed with water and dried. The product is further dissolved in dioxane on heating and allowed to cool to room temperature. The contents are filtered and dried under vacuum to obtain (−)-6-(4-aminophenyl)-5-methylpyridazin-3-(2H)-one crystalline solid. The pure (−)-6-(4-aminophenyl)-5-methylpyridazin-3-(2H)-one compound is then treated with sodium nitrite and malononitrile under acidic condition to obtain levosimendan. A disadvantage of the resolution process disclosed is that to obtain a high optical purity (99.5%) of the pyridazinone compound, recrystallisation with dioxane is required. Also the process involves multiple steps and is time consuming.

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