Sodium borohydride → benzhydryl (7R)-7-[[(2Z)-2-(2-amino-5-chloro-1,3-thiazol-4-yl)-2-trityloxyiminoacetyl]amino]-3-[[2-[2-[(2-methylpropan-2-yl)oxycarbonylamino]ethylsulfanylmethyl]-3-pyridinyl]sulfanyl]-8-oxo-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylate

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To a solution of (2-{3-[2-(2-tert-butoxycarbonylaminoethyl-sulfanylmethyl)-pyridin-3-yldisulfanyl]-pyridin-2-ylmethylsulfanyl}ethyl)carbamic acid tert-butyl ester (1.3 g, 0.0022 mol) in acetonitrile (120 mL) was added sodium borohydride (0.12 g, 0.003 mol), and the mixture was stirred at room temp. for 18 hours. (7R)-7-[(Z)-2-(2-amino-5-chlorothiazol-4-yl)-2-(triphenylmethoxyimino]-acetamido]-3-chloro-8-oxo-1-aza-bicyclo[4.2.0]oct-2-ene-2-carboxylate diphenylmethyl ester (3.6 g, 0.0043 mol) was added in portions and the mixture was heated at reflux for 6 hours. The solvent was evaporated and the residue was partitioned between ethyl acetate (50 mL) and water (50 mL). The organic layer was separated, dried over anhydrous MgSO4 and concentrated. The residue was treated with diethyl ether (50 mL), and the solid that formed was filtered and dried to give 3.6 g of crude product. The crude product was purified by column chromatography on silica gel (100 g), eluting with hexane: ethyl acetate 1:1, to give the title compound (1.15 g).

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