Amino acid bromides:a convenient choice for very difficult couplings

摘要

During the synthesis of pseudopeptides,many difficulties can be encountered for introduction of very hindered pseudoamino acids into a peptide chain.In the case of alpha-trifluoromethyl or difluoromethyl amino acids (alpha-Tfm or Dfm-AA),all methods known in modern peptide chemistry fail to afford peptides in significant yields.In fact,besides the steric hindrance,the polarizing effect of fluorine renders the amino function totally unreactive.