Studies in Thiohydantoin Chemistry. II. C-Terminal Sequencing of Peptides

Abstract

An investigation has been carried out into the thiocyanate degradation (AcOH/Ac₂O/HSCN) procedure as it relates to the C-terminal sequencing of peptides, particular emphasis being placed on the sequencing of amino acid residues containing sensitive or functional side chains. Attempted C-terminal sequencing of several serine- and threonine -containing peptides stopped at these particular residues, and did not proceed further. It is concluded that sequencing of most of the common amino acids is achievable but that significant problems will have to be overcome before routine sequencing of proline , serine, threonine, arginine , and, in particular, aspartic and glutamic acids can be claimed. The action of base on the thiohydantoin derivatives of N,S- diacetylcysteine and N,S- diacetyl-β-methylcysteine causes β-elimination of thioacetic S-acid to give the corresponding olefinic thiohydantoins.