4-{(2R,3S)-3-[(R)-1-(4-Nitro-benzyloxycarbonyloxy)-ethyl]-4-oxo-azetidin-2-yl}-3-oxo-butyric acid 4-nitro-benzyl ester

(3R,4R)-3-<(R)-1-(tert-butyldimethylsilyloxy)ethyl>-4-methylsulfonyl-2-azetidinone

methyl 3-methyl-2-[(3S,4R)-4-{2-(p-nitrobenzyloxycarbonylmethyl)allyl}-3-[(1S)-1-(p-nitrobenzyloxycarbonyloxy)ethyl}-2-oxoazetidin-1-yl]but-2-enoate