p-nitrobenzyl (5R,6S)-6-<(1R)-hydroxyethyl>-2-(2-p-nitrobenzyloxycarbonylaminoethyl)-2-penem-3-carboxylate

p-nitrobenzyl (5R,6S)-6-<(1R)-(tert-butyldimethylsiloxy)ethyl>-2-(2-p-nitrobenzyloxycarbonylaminoethyl)-2-penem-3-carboxylate

p-nitrobenzyl (5R,6S)-6-<(1R)-(tert-butyldimethylsiloxy)ethyl>-2-(3-p-nitrobenzyloxycarbonylaminopropan-1-yl)-2-penem-3-carboxylate

p-nitrobenzyl 2-<(3S,4R)-3-<(1R)-(tert-butyldimethylsiloxy)ethyl>-4-(3-p-nitrobenzyloxycarbonylaminopropionylthio)-2-oxoazetidin-1-yl>-2-hydroxyacetate

p-nitrobenzyl 2-<(3S,4R)-3-<(1R)-(tert-butyldimethylsiloxy)ethyl>-4-(3-p-nitrobenzyloxycarbonylaminopropionylthio)-2-oxoazetidin-1-yl>-2-triphenylphosphoranylideneacetate