Directed N-Terminal Elongation of Unprotected Peptides Catalyzed by Cathepsin C in Water

N-terminal chain extension of unprotected amino acid amides and peptides with dipeptide amides using Cathepsin C (dipeptidyl aminopeptidase I, EC 3.4.14.1)-mediated reverse proteolysis in water was studied. Taking Pro-X-NH₂ as the acyl donor, the sensitivity of the kinetically controlled peptide, coupling to pH value, temperature, acetonitrile addition, and nucleophile type were investigated. Basic or hydrophobic amino acids as the α-amino-N-nucleophile proved to be much more prone to catalyzed bond formation than their neutral, hydrophilic, or negatively charged analogues. In a preparative run a pentapeptide was obtained with 83% yield by directed and regioselective coupling of ProTrpNH₂ with LysLeuPheNH₂ catalyzed by Cathepsin C in aqueous buffer.