Exploration of lipase-catalyzed direct amidation of free carboxylic acids with ammonia in organic solvents

Abstract

Lipase-catalyzed direct amidation of free carboxylic acids is possible with ammonia in organic solvents. For butyric acid as a model compound the reaction proceeds well despite precipitation of ammonium butyrate, provided that the added molar amounts of butyric acid and ammonia are in the same range. The addition of ammonium salts is a convenient way to ensure suitable ammonia concentrations. Using Candida antarctica lipase B as the biocatalyst, the amidation proceeds well for various carboxylic acids and is very enantioselective in the amidation of 4-methyloctanoic acid.