(6R,7R)-3-(Acetoxymethyl)-8-oxo-7-(2-phenylacetamido)-5-thia-1-azabicyclo(4.2.0)oct-2-en-2-carbonsaeure 3-(Acetoxymethyl)-8-oxo-7-(phenylacetamido)-5-thia-1-azabicyclo(4.2.0)oct-2-ene-2-carboxylic acid