Thionation of di and tripeptides employing thiourea as a sulphur transfer reagent

A simple and efficient method for the synthesis of thiopeptides by the treatment of N α -protected peptide esters employing DMF/PCl 5 and thiourea as a sulphur transfer reagent is described. The conversion is carried out at room temperature within a short reaction time. The method is high yielding and free from racemization. Multiple thionation is demonstrated by conversion of two peptide bonds of tripeptides into thioamides. In addition, amino acid derived arylamides are also converted into aryl thioamides.