Peptide bond formation mediated by 4,5-dimethoxy-2-mercaptobenzylamine after periodate oxidation of the N-terminal serine residue.

[reaction in text] A thiol linker-attached peptide was prepared from a nonprotected peptide via an N(alpha)()-alpha-oxoacyl peptide. Selective oxidation of the N-terminal serine with sodium periodate gave the N(alpha)-glyoxyloyl peptide, reductive amination of which with 4,5-dimethoxy-2-(triphenylmethylthio)benzylamine gave an N(alpha)-4,5-dimethoxy-2-mercaptobenzyl glycyl peptide after removal of the trityl group. The N(alpha)-4,5-dimethoxy-2-mercaptobenzyl peptide can be condensed with a peptide thioester, and the linker is removable. This strategy provides a useful method for the synthesis of peptides using recombinant proteins.