(2R,7S,8S)-9-oxo-8t-[(R)-1-hydroxyethyl]-6-acetyl-1-azatricyclo[5.2.0.02,4]nonane-2,6-dicarboxylic acid 2-allyl ester 6-ethyl ester

(2S,2aS,2bS,5aS,6R)-2-((R)-1-Hydroxy-ethyl)-2b-methyl-1,4-dioxo-octahydro-3-oxa-6a-aza-cyclobuta[a]pentalene-6-carboxylic acid benzyl ester

1-(4-{[(2R,3S)-3-((1R)-1-{[tert-butyl(dimethyl)silyl]oxy}ethyl)-4-oxoazetidin-2-yl]acetyl}phenyl)-3-methylimidazolidin-2-one

{(2R,3S)-3-[(S)-1-(tert-Butyl-dimethyl-silanyloxy)-ethyl]-2-[2-(4-nitro-benzyloxycarbonylamino)-ethylsulfanylthiocarbonylsulfanyl]-4-oxo-azetidin-1-yl}-hydroxy-acetic acid 4-nitro-benzyl ester

Sodium; (5R,6S)-3-(2-ethoxy-ethylsulfanyl)-6-((R)-1-hydroxy-ethyl)-7-oxo-4-thia-1-aza-bicyclo[3.2.0]hept-2-ene-2-carboxylate