Polymer attached cyclic dipeptides as catalysts for enantioselective cyanohydrin formation

Abstract

Derivatives of cyclo-[(S)-Tyr-(S)-His], related to the 'Inoue' catalyst, cyclo-[(S)-Phe-(S)-His] have been attached to chloromethylated polystyrene and to polysiloxane polymers via spacer groups coupled to the tyrosine phenolic residue. These polymer-attached dipeptides have been shown to be efficient catalysts for the conversion of aromatic aldehydes to cyanohydrins but enantioselectivities are low. The loss of enantioselectivity relative to the Inoue catalyst has been attributed to steric effects from the substituents on the tyrosyl phenolic group. Some mechanistic comments regarding the preferred conformation of the active dipeptide are made. © 1992.