C-Terminal Sequencing of Peptides: An Investigation of the Iminohydantoin Method

Abstract

A method for the C-terminal sequencing of peptides was briefly outlined at a conference in 1975, but no further results have been reported since. This method converts the carboxy group into an acyl-S-alkylisothioureide, which on treatment with base reportedly gives the acylcyanamide. Following cyclization and hydrolysis, the iminohydantoin corresponding to the C-terminal residue is formed. Thus the peptide chain is shortened by one residue at each cycle.

Using model peptides, we have prepared authentic samples of the supposed products at each step, and have shown that the acylcyanamide is not an intermediate in this reaction. With glycine as the C-terminal residue, the iminohydantoin is obtained in near-quantitative yield.