210 μl of diisopropylethylamine and 250 μl of diphenylphosphoryl chloride were simultaneously added, whilst ice-cooling, to a solution of 400 mg of 4-nitrobenzyl (5R, 6S)-6-[(1R)-1-hydroxyethyl]-2-oxo-1-carbapenam-3-carboxylate dissolved in 5 ml of dry acetronitrile, and the mixture was stirred for 1 hour, whilst ice-cooling. At the end of this time, a solution of 447 mg of the crude (2S, 4S)-2-carbamoyl-1,1-dimethyl-4-mercaptopyrrolidinium salt prepared as described in Example 1-(1) in 5 ml of dry acetonitrile was added to the mixture, whilst ice-cooling, and then the mixture was allowed to stand for 4 hours at the same temperature and then for 2 days in a refrigerator. The reaction mixture was then poured into diethyl ether and the resulting deposit was washed repeatedly by decantation. The crude product was dissolved in a mixture of 30 ml of tetrahydrofuran and 30 ml of a 0.1M phosphate buffer (pH 7.0) and hydrogenated at room temperature for 2.5 hours in the presence of 450 mg of 10% w/w palladium-on-charcoal. At the end of this time, insoluble materials were removed by filtration using a Celite filter aid. The aqueous layer was concentrated by evaporation under reduced pressure, and the residue was transferred to a column packed with Diaion HP-20AG (Mitsubishi Chemicals Industries, Ltd.). Fractions eluted with water were collected and lyophilized to afford the title compound as a powder. This was further purified using a Lobar column (Merck, LiChroprep RP-8 size B) and fractions eluted with a 5% by volume aqueous methanolic solution were collected and concentrated by evaporation under reduced pressure followed by lyophilization, to afford 208 mg of the title compound.
