2-bromo-1-ethyl pyridinium tetrafluoroborate (BEP): A powerful coupling reagent for N-methylated peptide synthesis

2-Bromo-1-ethyl pyridinium tetrafluoroborate (BEP) was firstly utilized to the synthesis of peptides containing N-methyl amino acid residues both in s olution and solid phase, and demonstrated high reactivity, low racemization and excellent yields, which were approved by the successful synthesis of a series of oligopeptides and hindered peptide fragments, such as the 8-11 s egment of Cyclosporine A and the pentapeptide moiety of Dolastatin 15.