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

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

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

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

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