How does phenyl isothiocyanate, Ph-N=C=S, react with a peptide in the Edman degradation?

Question

Quizplus · Accepted Answer

Phenyl isothiocyanate reacts with the N-terminal amino acid of a peptide to form a phenylthiocarbamyl derivative. The sp carbon of the isothiocyanate group acts as an electrophile and attacks the amino group of the peptide, displacing the N-terminal amino acid and forming a stable thiourea linkage. This process is called the Edman degradation, and it is used to sequence peptides by removing and identifying one amino acid at a time from the N-terminus of the peptide.

How Does Phenyl Isothiocyanate, Ph-N=C=S, React with a Peptide in the Edman