Organocatalytic Peptide Modification

Significance

The tetraaminophosphonium salt 1-catalyzed formal quaternization of polypeptides is reported. The peptides were activated via dehydration, furnishing azlactones 2, which were reacted with various alkyl halides under biphasic conditions in the presence of chiral phase-transfer catalyst 1. The transformation led to the desired products 3 in high yields and excellent diastereoselectivities. These cyclic reaction products could then readily be reopened via direct ligation, giving rise to modified peptides.