(6R,7R)-3-(acetyloxymethyl)-7-[[(5R)-5-azaniumyl-6-oxido-6-oxohexanoyl]amino]-8-oxo-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylate (6R,7R)-3-(acetoxymethyl)-7-[[(5R)-5-azaniumyl-6-oxido-6-oxo-hexanoyl]amino]-8-oxo-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylate (6R,7R)-3-(acetoxymethyl)-7-[[(5R)-5-ammonio-6-oxido-1,6-dioxohexyl]amino]-8-oxo-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylate (6R,7R)-3-(acetoxymethyl)-7-[[(5R)-5-ammonio-6-keto-6-oxido-hexanoyl]amino]-8-keto-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylate (6R,7R)-3-(acetyloxymethyl)-7-[[(5R)-5-azaniumyl-6-oxido-6-oxo-hexanoyl]amino]-8-oxo-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylate