Synthesis of cyclic peptide hemicryptophanes: enantioselective recognition of a chiral zwitterionic guest.

The synthesis of the first members of a new class of cyclic peptide-containing hemicryptophanes is described. Synthesis was achieved through attachment of veratryl groups to the L-tyrosine side chains of a cyclic hexapeptide, c(YG)3, followed by intramolecular cyclodehydration to generate the CTV unit. The diastereomeric P- and M-hemicryptophanes were generated in a 2 : 1 ratio and were separated by chromatography. The enantioselective binding properties of the hemicryptophanes were investigated by complexation with carnitine. Both isomers were found to have significant selectivity for binding (R)-carnitine.