To a solution of S-methyl--N--[4-(phenoxy)benzenesulfonyl]-D-penicillamine methyl ester (0.250 g., 0.610 mmol) in DMSO (3 mL) at room temperature was added sodium thiomethoxide (171 mg., 2.44 mmol) in one portion. The solution was heated at 45° C. for18 hours, and then cooled to 0° C. and acidified to pH=5 using 1N aqueous sodium bisulfate. The mixture was partitioned between ethyl acetate and water, and the organic phase was washed with brine, dried over MgSO4, and concentrated. The residue was purified on silica eluting with 8 to 12% methanol in dichloromethane to give S-methyl--N--[4-(phenoxy)benzenesulfonyl]-D-penicillamine as a white solid in 95% yield: mp 156-158° C.; 1H--NMR (DMSO-d6) δ 1.28 (s, 3H), 1.31 (s, 3H), 1.97 (s,3H), 7.08-7.82 (m, 10H).
