(Z)-2-{(2R,3S)-2-[(2R,3S)-1-((Z)-1-Benzhydryloxycarbonyl-3-hydroxy-2-methyl-propenyl)-4-oxo-3-phenylacetylamino-azetidin-2-yldisulfanyl]-4-oxo-3-phenylacetylamino-azetidin-1-yl}-4-hydroxy-3-methyl-but-2-enoic acid benzhydryl ester