The Chemistry of Sequential Degradation

The degradation is based upon a reaction first described by Bergmann and Miekeley and further developed by Abderhalden and Brockmann in which phenylisocyanate reacts with the a-amino group of the terminal amino acid of a peptide chain, yielding a phenylcarbamyl derivative. This can be cyclisized 

this chemical sequential degradation is generally performed in the following distinct stages 10,11,12,13, (Pig. l). 

In the first stage — coupling — a phenylisothiocyanate (PITC) is reacted with the a-amino group of the N-terminal residue to form a phenylthiocarbamyl (PTC) derivative. 

In the second stage — cleavage — this terminal amino acid is released from the chain and forms an anilinothiazolinone (ATZ) ring. 

Finally, in a third stage — conversion — the unstable thiazolinone is converted into a phenylthiohydantoine (PTH) derivative which can be identified. 

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