Synthesis of peptides with narrow molecular weight distributions via exopeptidase-catalyzed aminolysis of hydrophobic amino-acid alkyl esters

A new synthesis technique that produces homogeneous oligopeptides that are essential for the formation of self-assembled structures is described. In contrast with endopeptidases, exopeptidases, which catalyze the cleavage of terminal peptide bonds, can potentially prevent unexpected hydrolysis during aminolysis. This is the first report on exopeptidase-catalyzed oligopeptide synthesis. Oligo(L-leucine) was synthesized using the exopeptidase carboxypeptidase Y (CPDY), which also prevented enzymatic hydrolysis. A high yield of oligo(L-leucine) with a narrow polydispersity (PDI) was obtained by limiting polypeptide cleavage during aminolysis. The reaction conditions, such as the temperature, pH, CPDY and substrate concentrations, were optimized to produce the best yields, molecular weights and PDI of the oligomers. Hydrophobic L-leucine methyl ester and L-isoleucine methyl ester were found to be the appropriate substrates for CPDY-catalyzed oligomerization; however, no oligomers were obtained using hydrophilic amino-acid esters. Oligomer yields were also affected by the amino-acid ester groups. Remarkably, the PDI of the oligomers was as low as 1.0, regardless of the reaction conditions and types of substrates used. Thus, exopeptidase-catalyzed oligomerization may become an alternative route for the current endopeptide-catalyzed oligomerization of peptides.