(R)- and (S)-cyanohydrins : their enzymatic synthesis and their reactions

Abstract

The known enzymes (R)- and (S)-oxynitrilase catalyze the enantioselective addition of hydrocyanic acid to ldehydes to give (R)- and (S)-cyanohydrins. The optical yields can distinctly be improved by the application of organic solvents (i.e. ethyl acetate or diisopropyl ether) instead of a waterjethanol mixture which was used previously in these reactions. For the enzyme (S)-oxynitrilase Sorghum bicolor evolved to be the best source. The optically active cyanohydrins can be transformed without any racemization by acid catalyzed hydrolysis into a-hydroxy acids and by hydrogenation with lithiumjaluminum hydride into 1,2-amino alcohols. Via addition of Grignard reagents to the O-protected cyanohydrins and follow-up hydrogenation, 1,2-amino alcohols are gained with very high diastereoselectivity. By O-sulfonylation of the (R)- and (S)-cyanohydrins optically active α-sulfonyloxy nitriles are obtained. These nitriles react with various nucleophiles by complete inversion of configuration to form various α-substituted carboxylic acid derivatives, α-azido nitriles, α-amino nitriles, α-amino acids, etc.