{(2R,3S)-3-[(R)-1-(tert-Butyl-dimethyl-silanyloxy)-ethyl]-2-[4-(4-nitro-benzyloxycarbonylamino)-butylsulfanylthiocarbonylsulfanyl]-4-oxo-azetidin-1-yl}-hydroxy-acetic acid 4-nitro-benzyl ester

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

{(2R,3S)-3-[(R)-1-(tert-Butyl-dimethyl-silanyloxy)-ethyl]-2-[4-(4-nitro-benzyloxycarbonylamino)-butylsulfanylthiocarbonylsulfanyl]-4-oxo-azetidin-1-yl}-(triphenyl-λ5-phosphanylidene)-acetic acid 4-nitro-benzyl ester

Trithiocarbonic acid (2R,3S)-3-[(R)-1-(tert-butyl-dimethyl-silanyloxy)-ethyl]-4-oxo-azetidin-2-yl ester 4-(4-nitro-benzyloxycarbonylamino)-butyl ester