Enzymatic synthesis of C-terminal arylamides of amino acids and peptides.

A mild and cost-efficient chemo-enzymatic method for the synthesis of C-terminal arylamides of amino acid and peptides is described. Using the industrial serine protease Alcalase under near-anhydrous conditions, C-terminal arylamides of N-Cbz-protected amino acids and peptides could be obtained from the corresponding C-terminal carboxylic acids, methyl (Me) or benzyl (Bn) esters, in high chemical and enantio- and diastereomeric purities. Yields ranged between 50% and 95% depending on the size of the aryl substituents and the presence of electron-withdrawing substituents. Complete alpha-C-terminal selectivity could be obtained even in the presence of various unprotected side-chain functionalities such as beta/gamma-carboxyl, hydroxyl, and guanidino groups. In addition, the use of the cysteine protease papain and the lipase Cal-B gave anilides in high yields. The chemo-enzymatic synthesis of arylamides proved to be completely free of racemization, in contrast to the state-of-the-art chemical methods.