tert-Butyl esters of tripeptides based on Pro-Phe as organocatalysts for the asymmetric aldol reaction in aqueous or organic medium

The enantioselective aldol reaction between ketones and aldehydes constitutes one the most common reaction models for the evaluation of novel organocatalysts. The last few years, it has been shown that the organocatalytic aldol reaction can be performed in water. A family of tripeptides consisting of proline, phenylalanine, and tert-butyl esters of amino acids was successfully employed in this asymmetric transformation. The products of the reaction between various ketones and aldehydes were obtained in high yields (up to 99%) with excellent diastereo- (up to 97:3 dr) and enantioselectivities (up to 99% ee). The C-terminal amino acid determines the ability of the tripeptide (Pro-Phe-AA-O^tBu) to act efficiently in aqueous or organic medium.