Abstract
Thrombin-catalyzed peptide synthesis has been studied using nine series of "inverse substrates, " i.e., p-amidinophenyl, p- and m-guanidinophenyl, p- and m-(guanidinomethyl)phenyl, and four position isomers of guanidinonaphthyl esters derived from Nα-(tert-butyloxycarbonyl)amino acid as acyl donor components. These substrates were classified into two types with respect to their response to thrombin. One group includes p-amidino- and p-guanidinophenyl esters, which undergo less enantioselective coupling reaction. Substrates classified into the other group are m-guanidinophenyl, p- and m-(guanidinomethyl)phenyl, and four position isomers of guanidinonaphthyl esters which are involved in the enantioselective coupling reaction. Thus amino acid residues of L-series (in the present case; Nα-Boc-L-Ala) are readily coupled to afford peptides by assigning them to either of the inverse substrates. The optimum condition for the coupling reaction was studied by changing organic solvent, pH, and acyl acceptor concentration. It was found that the enzymatic hydrolysis of the resulting product was negligible.
