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)