3.5 Grams of Z-Arg(Tos)-Ser-Ser-OMe was dissolved in 50 ml of methanol and 10 ml of water, and 8.06 ml of 1N-sodium hydroxide was added thereto, the mixture was stirred at a room temperature for 45 minutes, next 7.24 ml of 1N-HCl was added to neutralize the reaction mixture, then methanol was removed by distillation, and the residue was extracted with n-butanol. The extract was washed with water, and n-butanol and water were removed by distillation, the residue was crystallized by adding ether, reprecipitated from methanol-ethyl acetate to obtain 2.60 g of Z-Arg(Tos)-Ser-Ser-OH.
