The coupling between the carbamoylmethyl ester of an N-protected amino acid or dipeptide (at 25 mM) and an amino acid amide (at 100 mM) was achieved using Aspergillus melleus protease in 1, 1,1,3,3,3-hexafluoro-2-propanol/N, N-dimethylformamide (1: 1, v/v); the coupling efficiencies were dependent largely on the combination of amino acid residues: e.g. the dipeptide yields after 48 h were for L-Ala + Gly, similar to100% and for L-Leu + L-Leu, 16%.