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

4-nitrobenzyl 2-((2R,3S)-3-((R)-1-((tert-butyldimethylsilyl)oxy)ethyl)-2-((((2-((((4-nitrobenzyl)oxy)carbonyl)amino)ethyl)thio)carbonothioyl)thio)-4-oxoazetidin-1-yl)-2-(triethoxy-l5-phosphaneylidene)acetate