Amino acids 9-methyl thiocarboxylates

Methyl thiocarboxylates are very suitable for the V-thioacylation of V-unprotected amino acids. Thus, shaking a heterogenous mixture of PhCSOMe in ether and the amino acid in aq. NaOH gives g(X)d yields of V-thiobenzoylated material. Using (9-alkyl thiocarboxylates of amino acids (2 R = R NHCHR ), the approach has been extended to synthesize endothiopeptides such as (5) formation of imidates may interfere with the desired process. The reaction has been carried out in water/THF using NazCOj or as shown in equation (3). ... 

DCC can be used to prepare 5-alkyl and 5-aryl thiocarboxylates (1) from carboxylic acids and thiols according to equation (5). This method has been successfully applied to the synAesis of thiol esters with sensitive substituents, e.g. 5-methyl thioacrylate, a natural product. In particular, N-protected amino acid and peptide 5-phenyl esters, which are useful building blocks in peptide synthesis, are obtained in excellent yields without racemization. N-Hydroxyphthalimide and DMAP have been used as cocatalysts to facilitate the reaction. The preparation of the Wittig reagent (5) by this route is shown in equation (6). 

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