1-Azabicyclo[3.2.0]hept-2-ene-2-carboxylic acid,3-[[1-[(1,6-dihydro-6-oxo-3-pyridinyl)carbonyl]-3-azetidinyl]thio]-6-[(1R)-1-hydroxyethyl]-4-methyl-7-oxo-, (4-nitrophenyl)methyl ester,(4R,5S,6S)-