0.45 g (3.41 mmol) of sodium thiophenolate was added to a solution of 1.23 g (3.08 mmol) of (4R)-1-t-butoxycarbonyl-4-(p-toluenesulfonyloxy)-N-t-butyl-L-prolinamide [prepared as described in Preparation 6(a)] in 10 ml of a 2:1 by volume mixture of dimethylformamide and ethyl acetate, and the mixture was stirred for 3 hours. At the end of this time, the reaction mixture was poured into a 10% w/v aqueous solution of sodium hydrogen-carbonate and extracted with ethyl acetate. The organic extract was dried over anhydrous sodium sulfate, and then the solvent was removed by distillation under reduced pressure. The resulting residue was purified by preparative thin layer chromatography, using a 1:3 by volume mixture of ethyl acetate and hexane as the developing solvent, to give 1.0 g of the title compound as a colorless powder, melting at 119°-121° C.
