Compound Ia, e.g., ({[3-(biphenyl-4-ylsulfonyl)-1,3-thiazolidin-2-yl]carbonyl}amino)-(phenyl)acetic acid (500 mg, 1.04 mmol) was dissolved in THF (10 mL). Ammonia in dioxane (0.5N, 3.11 mL, 1.55 mmol) was added followed by HOBt (210 mg, 1.55 mmol) and DMAP (6 mg, 0.05 mmol). EDC.HCl (298 mg, 1.55 mmol) was finally added. The mixture was stirred for 5 hours at RT. As the reaction was complete, it was diluted with EtOAc, washed with 5% citric acid, NH4Cl sat, NaHCO3 sat, brine and dried over MgSO4. After filtration and evaporation of the solvents, the resulting crude product was purified by flash chromatography (Cyclohexane/EtOAc, gradient from 1:1 to 0:1). Compound Ib, e.g. N-(2-amino-2-oxo-1-phenylethyl)-3-(biphenyl-4-ylsulfonyl)-1,3-thiazolidine-2-carboxamide, was isolated in 90% purity by HPLC (349 mg, 80% yield).
