2-{(2R,3R)-3-(1,3-Dioxo-1,3-dihydro-isoindol-2-yl)-2-[(Z)-2-hydroxy-1-(4-nitro-benzyloxycarbonyl)-propenylsulfanyl]-4-oxo-azetidin-1-yl}-3-methyl-but-2-enoic acid benzyl ester
secopenicillin
(Z)-2-[(2R,3R)-1-((R)-1-Benzyloxycarbonyl-2-methyl-allyl)-3-(1,3-dioxo-1,3-dihydro-isoindol-2-yl)-4-oxo-azetidin-2-ylsulfanyl]-3-hydroxy-but-2-enoic acid 4-nitro-benzyl ester
2-{(2R,3R)-3-(1,3-Dioxo-1,3-dihydro-isoindol-2-yl)-2-[(Z)-2-hydroxy-1-(4-nitro-benzyloxycarbonyl)-propenylsulfanyl]-4-oxo-azetidin-1-yl}-3-methyl-but-2-enoic acid benzyl ester
4-nitrobenzyl 2-diazo-3-oxo-butanoate
{(2R,3R)-3-(1,3-Dioxo-1,3-dihydro-isoindol-2-yl)-2-[(2-methyl-[1,3]dioxolan-2-yl)-(4-nitro-benzyloxycarbonyl)-methylsulfanyl]-4-oxo-azetidin-1-yl}-hydroxy-acetic acid 4-nitro-benzyl ester
(5R,6R)-6-(1,3-Dioxo-1,3-dihydro-isoindol-2-yl)-7-oxo-4-thia-1-aza-bicyclo[3.2.0]hept-2-ene-2,3-dicarboxylic acid bis-(4-nitro-benzyl) ester
(6R,7R)-7-(1,3-Dioxo-1,3-dihydro-isoindol-2-yl)-3-methyl-8-oxo-5-thia-1-aza-bicyclo[4.2.0]oct-3-ene-2,4-dicarboxylic acid bis-(4-nitro-benzyl) ester
Chloro-{(2R,3R)-3-(1,3-dioxo-1,3-dihydro-isoindol-2-yl)-2-[(2-methyl-[1,3]dioxolan-2-yl)-(4-nitro-benzyloxycarbonyl)-methylsulfanyl]-4-oxo-azetidin-1-yl}-acetic acid 4-nitro-benzyl ester
[(2R,3R)-3-(1,3-Dioxo-1,3-dihydro-isoindol-2-yl)-2-(4-nitro-benzyloxyoxalylsulfanyl)-4-oxo-azetidin-1-yl]-(triphenyl-λ5-phosphanylidene)-acetic acid 4-nitro-benzyl ester