4-[Carbomethoxymethyl]-6-[carboethoxy-3-phenyl propylamino]-perhydro-1,4-thiazepin-5-one (0.1 g) is dissolved in 1.5 ml of methanol and 0.5 ml of 1M sodium hydroxide. At the end of 4 hours at room temperature, 2 ml of water is added. The resulting solution is loaded onto a column of Dowex-50 resin (on the proton cycle). After thorough washing with water, the column is developed with 5% pyridine. The eluent is lyophilized to yield the product as a white solid (0.085 g). The sample analyzes for C17H23N2O5S.1/2H2O.
