Application of proteases in the C-terminal modification of peptides

The high selectivity and the mild reaction conditions of enzymatic processes prompted their application in the synthesis of peptides, where selectivity is a feature of pivotal importance. Here we report the use of the serine protease subtilisin for the selective deprotection of C-terminal tert-butyl esters, achieved in good to quantitative yield for most of the natural amino acids. The same enzyme was active in the C-terminal amidation affording excellent yields with several peptides in the presence of a variety of amino sources. Subtilisin, finally, can also catalyse the transesterification of C-terminal primary esters. All the reactions are highly selective and neither side chains modifications nor N-terminus reactions have been observed. The endopeptidase activity, an important drawback in the use of proteases, was minimized upon extensive optimization of the reaction conditions