(5R,6S)-6-[(R)-1-(tert-Butyl-dimethyl-silanyloxy)-ethyl]-3-(3-hydroxy-propylsulfanyl)-7-oxo-4-thia-1-aza-bicyclo[3.2.0]hept-2-ene-2-carboxylic acid 4-nitro-benzyl ester

p-nitrobenzyl 2-<(3S,4R)-3-<(1R)-(tert-butyldimethylsiloxy)ethyl>-4-propionylthio-2-oxoazetidin-1-yl>-2-hydroxyacetate

p-nitrobenzyl (5R,6S)-6-<(1R)-hydroxyethyl>-2-(4-p-nitrobenzyloxycarbonylaminobutan-1-yl)-2-penem-3-carboxylate

p-nitrobenzyl (5R,6S)-6-<(1R)-hydroxyethyl>-2-ethoxymethyl-2-penem-3-carboxylate