“…Residues (Xaa = Gly, Ala, Asn(Tr), Glu( t ‐Bu), His( N im ‐Tr), Ile, Leu, Lys(Boc), Phe, Pro, Ser( t ‐Bu), Thr( t ‐Bu), Tyr( t‐ Bu), Val, Sar, N α ‐Me‐Ala, N α ‐Me‐Leu) in the dipeptide sequences ( 57 ) were not significantly oxidized on side chains resulting in reasonably high yielding mixtures of syn‐cis and anti‐cis diastereomers (Scheme ). While in this case side chains were protected, unprotected residues such as Lys, Asn, Glu, Tyr, Ser and ornithine embedded in several peptide sequences were shown to be stable to DMDO exposure for 10 minutes at room temperature . Following the saponification of the N α ‐Tr‐HO‐HPIC‐Xaa‐OMe methyl ester, the resulting carboxylate was readily incorporated into a peptide sequence by standard peptide chemistry .…”