(2S,4S)-4-Mercapto-2-[2-(4-nitro-benzyloxycarbonylamino)-ethylsulfanylmethyl]-pyrrolidine-1-carboxylic acid 4-nitro-benzyl ester

(4R,5S,6S)-6-((R)-1-Hydroxy-ethyl)-4-methyl-3-{(3S,5S)-1-(4-nitro-benzyloxycarbonyl)-5-[2-(4-nitro-benzyloxycarbonylamino)-ethylsulfanylmethyl]-pyrrolidin-3-ylsulfanyl}-7-oxo-1-aza-bicyclo[3.2.0]hept-2-ene-2-carboxylic acid 4-nitro-benzyl ester