(6R,6'R)-3,3'-dimethyl-8,8'-dioxo-(6rH,6'r'H)-7t,7't'-carbonyldiamino-bis-(5-thia-1-aza-bicyclo[4.2.0]oct-2-ene-2-carboxylic acid) bis-(2,2-dimethyl-propionyloxymethyl) ester

(6R)-3,7c-dimethyl-8-oxo-7t-(2-phenyl-acetylamino)-(6rH)-5-thia-1-aza-bicyclo[4.2.0]oct-2-ene-2-carboxylic acid tert-butyl ester

(6R,7R)-7-[(R)-2-Amino-2-(2,3-dihydro-benzofuran-5-yl)-acetylamino]-3-methyl-8-oxo-5-thia-1-aza-bicyclo[4.2.0]oct-2-ene-2-carboxylic acid