To a solution of 3-{4-[2-(tert-butoxycarbonyl-heptyl-amino)-ethyl]-phenyl}-2-hydroxy-propionic acid ethyl ester (0.69 mmol, 300 mg) dissolved in pyridine (3 mL) was added methanesulfonyl chloride (0.69 mmol, 0.534 mL). The mixture was stirred at room temperature overnight. A portion of the reaction mixture (0.115 mmol) was added to a solution containing 2-propane thiol (0.115 mmol, 0.107 mL) dissolved in anhydrous CH2Cl2 (2 mL). To this stirred solution was added a 1M solution of potassium tert-butoxide in tetrahydrofuran (0.115 mmol, 0.115 mL). The mixture was stirred overnight then poured over 1 M HCl. The mixture was extracted with diethyl ether (3×). The organic layers were combined, washed with 1 M HCl (2×), saturated brine (2×), dried over Na2SO4, and concentrated to a crude film. The film was purified by chromatography on silica gel (Merck silica gel 60, art#9385-3) eluting with 20% ethyl acetate in hexanes to give 3-{4-[2-(tert-butoxycarbonyl-heptyl-amino)-ethyl]-phenyl}-2-isopropylsulfanyl-propionic acid ethyl ester as a clear film containing an approximate 1:1 mixture of methyl and ethyl ester (30.2 mg, 55%).
