(6R)-3-methyl-5ξ,8-dioxo-7t-phthalimido-(6rH)-5λ4-thia-1-aza-bicyclo[4.2.0]oct-2-ene-2-carboxylic acid methyl ester

(5R,6S)-6-(1,3-Dioxo-1,3-dihydro-isoindol-2-yl)-7-oxo-3-(tetrahydro-pyran-2-yloxymethyl)-4-thia-1-aza-bicyclo[3.2.0]hept-2-ene-2-carboxylic acid methyl ester

(6R)-3t-hydroxy-3c-methyl-8-oxo-7t-phthalimido-(6rH)-5-thia-1-aza-bicyclo[4.2.0]octane-2c-carboxylic acid methyl ester

(Z)-2-[(2R,3R)-2-(Benzothiazol-2-yldisulfanyl)-3-(1,3-dioxo-1,3-dihydro-isoindol-2-yl)-4-oxo-azetidin-1-yl]-3,4-dihydroxy-but-2-enoic acid methyl ester

2-((2R)-2r-benzothiazol-2-yldisulfanyl-4-oxo-3c-phthalimido-azetidin-1-yl)-3-methyl-but-2-enoic acid methyl ester