N-Hydroxypeptides have recently attracted attention for their distinct conformational and physicochemical properties, which markedly influence biological activity. However, incorporating N-hydroxyproline into peptide sequences is synthetically demanding, typically requiring complex transformations with several protection/deprotection steps that reduce efficiency and sustainability of the synthesis process. In this study, we present an innovative strategy for the N-hydroxylation of proline in peptides using an on-site oxidation strategy via Cope elimination under mild conditions. The methodology is showcased through the assembly of an N-hydroxylated derivative of melanostatin neuropeptide.

Our approach demonstrates that the N-(cyanoethyl) group serves as a protecting moiety during peptide synthesis and as a leaving group in the oxidation step. Using N-(cyanoethyl)-L-proline as the starting material, peptide coupling with H-L-Leu-Gly-OMe afforded a melanostatin intermediate that, upon treatment with m-chloroperbenzoic acid, underwent an efficient Cope elimination to introduce the N-hydroxy group at the proline residue.

This single-step oxidation under mild conditions delivered the desired tripeptide with excellent yield (93%), avoiding additional deprotection steps. Comparative experiments revealed that incorporating the N-(cyanoethyl) group earlier in the synthesis significantly improved the global yield (78%) relative to late-stage derivatization (41%).

Overall, this work presents a novel strategy for the selective modification of prolyl-containing peptides, exemplified by the assembly of N-hydroxy-melanostatin. This on-site oxidation methodology, based on Cope elimination, offers a valuable tool for the development of bioactive N-hydroxylated peptides.