The 2,2,2-Trichloroethyl Group for Carboxyl Protection During Peptide Synthesis

The 2,2,2-trichloroethyl esters of several N-carbobenzoxy-amino acids were prepared by reacting the corresponding acid chlorides with trichloroethanol and the carbobenzoxy groups were selectively removed by HBr–AcOH. The resulting esters were then coupled with various N-carbobenzoxy-amino acids or peptides using dicyclohexylcarbodiimide in acetonitrile to give N-carbobenzoxy-peptide trichloroethyl esters. The selective removal of the trichloroethyl protecting group was effected by reduction using zinc in acetic acid. The optical activity of the N-carbobenzoxy-peptides so obtained agreed well with the values reported in the literature. The overall results suggest that the 2,2,2-trichloroethyl group could be useful for carboxyl protection during peptide synthesis.