Stepwise Synthesis of Oligopeptides with N-Carboxy α-Amino Acid Anhydrides. V. Synthesis and NMR Study of Oligopeptides with Some Sequences of L-Alanine and L-Valine

Abstract

Oligopeptides with the sequences of alternating L-alanine and L-valine and of a short block of the two amino acids were synthesized in high yields by the NCA method in a heterogeneous system of acetonitrile–water. The NMR spectra of methyl protons in the side chains of the oligopeptides in TFA showed a clear difference in chemical shifts resulting from the sequential position, C-terminal, internal and N-terminal, of the amino acid residues in the oligopeptides. Deshielding effects of terminal carboxyl and ammonium groups as compared with that of peptide linkage was estimated from the spectra of the oligopeptides.