Photo-induced preparation of unnatural α-amino acids: synthesis and characterization of novel Leu5-enkephalin analogues

We here report the first example of the photo-induced preparation of unnatural α-amino acids and modification of peptides with unactivated alkyl chlorides (iodides) without the assistance of a transition metal catalyst or photosensitizer. The method was successfully applied for the late-stage modification of peptides and provided a novel enkephalin analogue with significantly better analgesic activity and 2.6-fold more long-lasting time compared to its parent peptide.