Peptide heterocycle conjugates: a diverted edman degradation protocol for the synthesis of N-terminal 2-iminohydantoins.

[reaction: see text] A modified Edman degradation procedure provides an effective means of introducing a heterocycle at the N-terminus of an alpha-amino acid amide or peptide. Reaction of a peptide with an isothiocyanate, followed by dehydrothiolative trapping of the intermediate thiourea, by intramolecular cyclization of the weakly nucleophilic adjacent amide nitrogen, generates an iminohydantoin. A solution-phase parallel synthesis of iminohydantoins and a polymer-supported synthesis of dipeptide- and tripeptide-derived iminohydantoins were also achieved.