(2S,5R,6S)-6-[1-(tert-Butyl-dimethyl-silanyloxy)-ethyl]-3-[1-tert-butylsulfanyl-meth-(E)-ylidene]-7-oxo-4-thia-1-aza-bicyclo[3.2.0]heptane-2-carboxylic acid 4-nitro-benzyl ester

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

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