(2S,6R)-3,3-Dimethyl-4,7-dioxo-6-phenylacetylamino-4λ4-thia-1-aza-bicyclo[3.2.0]heptane-2-carboxylic acid phenylacetoxymethyl ester
(R)-3-Methoxy-8-oxo-7-phenylacetylamino-5-thia-1-aza-bicyclo[4.2.0]oct-2-ene-2-carboxylic acid phenylacetoxymethyl ester
(2S,6R)-3,3-Dimethyl-7-oxo-6-phenylacetylamino-4-thia-1-aza-bicyclo[3.2.0]heptane-2-carboxylic acid phenylacetoxymethyl ester
(R)-3-Methyl-8-oxo-7-phenylacetylamino-5-thia-1-aza-bicyclo[4.2.0]oct-2-ene-2-carboxylic acid phenylacetoxymethyl ester