Amino acid bromides: Their N-protection and use in the synthesis of peptides with extremely difficult sequences

N-Protected ?-amino acid bromides were easily generated in situ with 1-bromo-N,N-2-trimethyl-1-propenylamine from the corresponding amino acids under very mild conditions. o-Nbs and the azido moieties proved to be compatible with these overactivated halides and were successfully applied in difficult peptide bond formations. N-Deprotection methods and the total step-by-step solution synthesis of a peptide containing up to seven consecutive L-(?Me)Valine residues are also reported. The assembly of this homopeptide was achieved in a short time and in very high yields by the azido/bromide system in a single repetitive operation.