1: N,N'-dicyclohexylcarbodiimide / ethyl acetate / 12 h / 4 °C 2: 84 percent / dimethylformamide / 12 h / 25 °C 3: 85 percent / alkaline mesintericopeptidase / H2O / 6 h / 25 °C / pH 8.0 4: 100 percent / phosphodiesterase I / H2O / 6 h / 37 °C / pH 8.8 View Scheme