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

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

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

p-nitrobenzyl (5R,6S)-6-<(1R)-hydroxyethyl>-2-<<(2S)-N-p-nitrobenzyloxycarbonylazeitidin-2-yl>methyl>-2-penem-3-carboxylate