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

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

(3S,4R)-3-<(1R)-(tert-butyldimethylsiloxy)ethyl>-4-<3-(p-nitrobenzyloxycarbonylamino)propionylthio>azetidin-2-one

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

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