Reaction Steps
4-Methoxybenzyl (6R, 7R)-7-phenylacetamido-3-(1,1-dioxotetrahydrothien-2-yl)ceph-2-em-4-carboxylate (0.973 g) in dichloromethane (20 ml) was cooled in ice-water and treated with 3-chloroperbenzoic acid (0.343 g) and warmed to room temperature for 1 h. The solution was washed with saturated sodium metabisulphite, brine and then dried. Afar removal of solvent, the residue was flash chromatographed on silica gel eluting initially with 80, 90% ethyl acetate-hexane and then ethyl acetate. The first product eluted was the least polar isomer of the title compound, obtained as a pale yellow foam, (0.309 g, 31%); 5H (CDCl3) 2.02-2.39 (4H, m), 2.91-3.03 (1H, m), 3.11-3.20 (1H, m), 3.49 and 3.79 (2H, ABq, J 8.6 Hz), 3.58 and 3.66 (2H, ABq, J 15.9 Hz), 3.81 (3H, s), 4.52 (1H, d, J 4.7 Hz), 5.02 (1H, dd, J 7.3, 11.2 Hz), 5.20 and 5.26 (2H, ABq, J 11.4 Hz), 6.03 (1H, dd, J 4.7, 10.0 hz), 6.69 (1H, d, J 10.0 Hz), 6.90 (2H, d, J 8.7 Hz) and 7.26-7.39 (7H, m). Further elution with 10% ethanol-ethyl acetate provided the second more polar isomer as an off white, amorphous solid, (0.166g, 17%); 5H (CDCl3) 1.90-2.30 (4H, m), 2.88-3.20 (2H, m), 3.06 a 4.13 (2H, ABq, J 18.4 Hz), 3.57 (2H, s), 3.77 (3H, s), 4.43 (1H, d, J 4.1 Hz), 4.61 (1H, t, J 8.3 Hz), 5.18 (3H, m), 5.98 (1H, dd J 4.8, 9.6 Hz), 6.84 (2H, d, J 8.7 Hz) and 7.17-7.36 (7H, m).
