4-Nitrobenzyl (2-{[(allyloxy)carbonyl]amino}-4-{[(2R,3S)-3-((1R)-1-{[tert-butyl(dimethyl)silyl]oxy}ethyl)-4-oxoazetidin-2-yl]acetyl}phenyl)acetate

(2S,2aS,2bR)-2-((R)-1-Methanesulfonyloxy-ethyl)-1-oxo-2,2a,2b,3,5,6-hexahydro-1H-4-thia-7a-aza-cyclobuta[a]indene-7-carboxylic acid allyl ester

(3S,4R)-3-[(R)-1-Hydroxyethyl]-4-[(phenylthio)carbonylmethyl]-2-azetidinone

{(2R,3S)-3-[(R)-1-(tert-Butyl-dimethyl-silanyloxy)-ethyl]-4-oxo-azetidin-2-yl}-thioacetic acid S-isopropyl ester

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