{(2R,3S)-2-(2-Allyloxycarbonylamino-ethylsulfanylthiocarbonylsulfanyl)-4-oxo-3-[(R)-1-(2,2,2-trichloro-ethoxycarbonyloxy)-ethyl]-azetidin-1-yl}-hydroxy-acetic acid allyl ester

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

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