Thioglycolic Acid → (2S,4S)-4-Mercapto-2-{4-[2-(p-nitrobenzyloxycarbonyl)oxyethyl]-1-piperazinylcarbonyl}-1-(p-nitrobenzyloxycarbonyl)pyrrolidine

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Reaction Steps

A solution of 36.5 g of diethyl azodicarboxylate in 100 ml of tetrahydrofuran was added dropwise, whilst ice-cooling, to a solution of 105 g of (2S,4R)-4-hydroxy-2-{4-[2-(4-nitrobenzyloxycarbonyl)oxyethyl]-1-piperazinylcarbonyl}-1-(4-nitrobenzyloxycarbonyl)pyrrolidine [prepared as described in steps 90(b)(i), 90(b)(i') and 90(b)(i") above] and 55 g of triphenylphosphine in 700 ml of tetrahydrofuran, and the resulting mixture was stirred at the same temperature for 10 minutes. A solution of 15.9 g of mercaptoacetic acid in 100 ml of tetrahydrofuran was then added dropwise to the mixture, and the mixture was stirred at room temperature for 1 hour. At the end of this time, the reaction mixture was concentrated by evaporation under reduced pressure, and the concentrate was dissolved in 1.5 liters of ethyl acetate. The resulting solution was then washed with water and with an aqueous solution of sodium chloride, in that order, after which it was dried over anhydrous sodium sulfate. The solvent was removed by distillation under reduced pressure, and then the residue was mixed with 400 ml of diisopropyl ether. The diisopropyl ether-soluble materials were extracted and discarded. The same extraction operations were repeated four times, and then the resulting residue was purified by column chromatography through 3 kg of silica gel, using a gradient elution method, with mixtures of ethyl acetate and methanol ranging from 1:0 to 20:1 by volume as the eluent, to give 88.4 g of the title compound, as a colorless powder.

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