Stereoselective micellar catalysis. Reactions of amino-acid ester derivatives with N-acyl-L-histidine in micelles
Mixed micelles of the N-acyl-L-histidines (I) and cetyltrimethylammonium bromide (CTABr) are effective stereoselective catalysts for cleavage of the enantiomeric amino-acid ester derivatives (II). The rate enhancements and stereoselective effects depend on the hydrophobicity of (I) in micelles, and an increase in the chain length of the acyl part of (I) increases both the reaction rates and the enantiomer rate ratio. Mixed micelles with anionic and nonionic surfactants are relatively less effective stereoselective catalysts. Kinetic analysis indicates that the stereoselectivity in mixed micelles is mainly determined by catalytic acyl transfer to the optically active imidazole group of (I).