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

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

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

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

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