(2S,2aS,2bS,5aS,6R)-2-[(R)-1-(tert-Butyl-dimethyl-silanyloxy)-ethyl]-2b-methyl-1,4-dioxo-octahydro-3-oxa-6a-aza-cyclobuta[a]pentalene-6-carboxylic acid benzyl ester

(2S,2aS,2bR,5aR,6S)-2-[(R)-1-(tert-Butyl-dimethyl-silanyloxy)-ethyl]-4-hydroxy-2b-methyl-1-oxo-5a-phenylsulfanyl-octahydro-3-oxa-6a-aza-cyclobuta[a]pentalene-6-carboxylic acid benzyl ester

(2S,2aS,2bR,5aR,6S)-2-[(R)-1-(tert-Butyl-dimethyl-silanyloxy)-ethyl]-2b-methyl-1,4-dioxo-5a-phenylsulfanyl-octahydro-3-oxa-6a-aza-cyclobuta[a]pentalene-6-carboxylic acid benzyl ester

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