Hydroxyl and carboxyl groups present in the peptide are to be first protected as amides or esters. Terminal carboxyl group is converted into an anhydride first and treated with iso-thiocyanate to give a C-terminal acyl thiocyanate peptide product. The product automatically rearranges to a thiohydantoin incorporating the penultimate C-terminal unit. Repetitive analyses may be conducted in much the same way they are with the Edman procedure to find the amino acid sequence in the chain.
