methyl (2S,5R,6S)-6-bromo-6-((R)-1-hydroxyethyl)-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]heptane-2-carboxylate

benzyl (2S,5R,6R)-6-<(R)-1-hydroxyethyl>penicillanate

(2S,5R,6R)-6-[(R)-1-(tert-Butyl-dimethyl-silanyloxy)-ethyl]-3,3-dimethyl-7-oxo-4-thia-1-aza-bicyclo[3.2.0]heptane-2-carboxylic acid benzyl ester

benzyl (2S,5R,6S)-6-<(R)-1-hydroxyethyl>-6-(phenylseleno)penicillanate

benzyl (2S,5R,6R)-6-<(R)-1-(t-butyldimethylsilyloxy)ethyl>penicillanate 1,1-dioxide