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

(3S,4S)-1-(allyloxycarbonylmethyl)-3-[(1R)-1-(tert-butyldimethylsilyloxy)ethyl]-4-{(1R)-1-[(3S,5S)-1-allyloxycarbonyl-5-dimethylaminocarbonylpyrrolidin-3-yl]thiocarbonylethyl}-2-azetidinone

(4R,5S,6S)-3-Benzylsulfanyl-6-((R)-1-hydroxy-ethyl)-4-methyl-7-oxo-1-aza-bicyclo[3.2.0]hept-2-ene-2-carboxylic acid allyl ester

allyl (4R,5S,6S)-6-[(1R)-1-(tert-butyldimethylsilyloxy)ethyl]-3-cyclohexylthio-4-methyl-7-oxo-1-azabicyclo[3.2.0]hept-2-ene-2-carboxylate

(4R,5R,6S)-6-[(R)-1-(tert-Butyl-dimethyl-silanyloxy)-ethyl]-3-(diphenoxy-phosphoryloxy)-4-methyl-7-oxo-1-aza-bicyclo[3.2.0]hept-2-ene-2-carboxylic acid allyl ester