Chemoselective Wittig and Michael ligations of unprotected peptidyl phosphoranes in water furnish potent inhibitors of caspase-3.

Abstract

Unprotected peptidyl phosphoranes 1 with sequence Ac-L-aspartyl-L-glutamyl-L-valinyl-L-aspartyl are released from polymer support and react with aliphatic and aromatic aldehydes in aqueous medium in a Wittig ligation. Obtained vinyl ketones 6-12 are potent inhibitors of caspase-3. Vinyl ketone 6, derived from formaldehyde, undergoes Michael ligations with thiol nucleophiles furnishing products 14-16, also in aqueous medium. The demonstrated ligation reactions enable the modification of complex functionalized peptides in water providing bioactive protein ligands without side-chain protection.