Since the pioneering studies in the 1950s by Wieland, who was inspired by the biosynthetic use of S-acetyl-coenzyme A, thiocarboxylic acid derivatives have served in various approaches for peptide bond formation, most notably, native chemical ligation. For example, dipeptides have been synthesized in a two-step process entailing thioacid synthesis using thioacetic acid and sodium hydrogen sulphide. Oxidative dimerization of the thioacids to the diacyl disulfide followed by amino acylation was shown to give dipeptides without racemization. 41