T3P (propylphosphonic anhydride) mediated conversion of Nα-protected amino/peptide acids into thioacids

A general, mild and an efficient protocol, which makes use of T3P as an acid activator for the synthesis of Nα-protected amino/peptide thioacids from corresponding acids in the presence of finely ground Na2S as hydrosulfide ion donor is described. The protocol employed significantly increases the overall efficiency as the yield, reaction duration and purity of even sterically hindered amino acids.