(5R,6S)-6-((R)-1-hydroxyethyl)-2-[(1-tetrahydro-2-furyl)ethyl]penem-3-carboxylic acid allyl ester

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

(3S,4S)-3-[(R)-1-(tert-butyldimethylsilyloxy)ethyl]-4-[1,1-di(allyloxycarbonyl)ethyl]-2-azetidinone

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

(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-carboxylic acid 4-nitro-benzyl ester