4-{(2R,3S)-1-(tert-Butyl-dimethyl-silanyl)-3-[(S)-1-(tert-butyl-dimethyl-silanyloxy)-ethyl]-4-oxo-azetidin-2-yl}-3-oxo-butyric acid 4-nitro-benzyl ester
Carbonic acid 5-{(5R,6S)-6-((R)-1-hydroxy-ethyl)-3-[2-(4-nitro-benzyloxycarbonylamino)-ethylsulfanyl]-7-oxo-1-aza-bicyclo[3.2.0]hept-2-en-2-yl}-tetrazol-1-ylmethyl ester 4-nitro-benzyl ester
Trifluoro-methanesulfonic acid (5R,6S)-6-((R)-1-hydroxy-ethyl)-2-[1-(4-nitro-benzyloxycarbonyloxymethyl)-1H-tetrazol-5-yl]-7-oxo-1-aza-bicyclo[3.2.0]hept-2-en-3-yl ester
Carbonic acid 5-[(5R,6S)-3-(N,N-dimethyl-carbamimidoylmethylsulfanyl)-6-((R)-1-hydroxy-ethyl)-7-oxo-1-aza-bicyclo[3.2.0]hept-2-en-2-yl]-tetrazol-1-ylmethyl ester 4-nitro-benzyl ester
Carbonic acid 5-[(5R,6S)-6-((R)-1-hydroxy-ethyl)-7-oxo-3-phenylsulfanyl-1-aza-bicyclo[3.2.0]hept-2-en-2-yl]-tetrazol-1-ylmethyl ester 4-nitro-benzyl ester