(2S,5R,6S)-6-((R)-1-Hydroxy-ethyl)-3,3-dimethyl-4,7-dioxo-4λ4-thia-1-aza-bicyclo[3.2.0]heptane-2-carboxylic acid methyl ester

2-{(2R,3S)-2-((E)-3-Acetoxy-1-acetoxymethyl-propenylsulfanyl)-3-[(R)-1-(4-nitro-benzyloxycarbonyloxy)-ethyl]-4-oxo-azetidin-1-yl}-3-methyl-but-2-enoic acid methyl ester

{(2R,3S)-2-(2-Acetoxy-acetylsulfanyl)-3-[(R)-1-(4-nitro-benzyloxycarbonyloxy)-ethyl]-4-oxo-azetidin-1-yl}-(triphenyl-λ5-phosphanylidene)-acetic acid 2-oxo-propyl ester

Acetic acid (2R,3S)-3-[(R)-1-(4-nitro-benzyloxycarbonyloxy)-ethyl]-4-oxo-azetidin-2-ylsulfanylcarbonylmethyl ester

(5R,6S)-3-Acetoxymethyl-6-[(R)-1-(4-nitro-benzyloxycarbonyloxy)-ethyl]-7-oxo-4-thia-1-aza-bicyclo[3.2.0]hept-2-ene-2-carboxylic acid 2-oxo-propyl ester