<4R,3S(R)>-3-<1(R)-1-<(tert-butyldimethylsilyl)oxy>ethyl>-4-<<<(tert-butyldimethylsilyl)oxy>acetyl>thio>-2-azetidinone

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

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

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

p-nitrobenzyl(5R,6S)-6-[1(R)-hydroxyethyl]-2-hydroxymethyl-penem-3-carboxylate