Ultrasound accelerated conversion of Nalpha-urethane protected peptide esters to their thiopeptides using P2S5.

A fast and efficient synthesis of N(alpha)-protected thiopeptide esters from the corresponding peptide esters using P(2)S(5) as thionating agent assisted by ultrasonication has been described. The conversion of peptide bond into thioamide was complete in 20-40 min at rt. The reaction was accomplished without using any base. The products isolated were characterized using (1)H NMR, (13)C NMR and mass spectroscopy.