Non-coded amino acids as acyl donor substrates for peptide bond formation catalyzed by thermoase in toluene

The peptide bond formation of N-protected non-coded amino acids having different structures as acyl donor substrates that is catalyzed by thermoase in organic media was investigated. In these reactions, N-protected l-α-non-coded amino acids, including l-Orn, l-Cit, α-aminobutyric acid (l-α-Abu) and phenylalanine homologues, were used as the acyl donors and phenylalanine derivatives were used as the acyl acceptors. This kind of enzymatic reactions cannot be carried out in an aqueous buffer due to the rigid specificity of proteases to coded amino acids in water. The results demonstrated that the substrate specificity of proteases could be broadened in organic solvents. In addition, the factors that influenced these protease-catalyzed reactions, including structures of the substrates, water content and the bases used, were systematically studied. Our work provided important evidence for broadening the application of protease in organic synthesis.