{(2R,3S)-3-[(R)-1-(tert-Butyl-dimethyl-silanyloxy)-ethyl]-2-[(1R,4R)-4-(2-methoxy-ethyl)-2-oxo-cyclohexyl]-4-oxo-azetidin-1-yl}-oxo-acetic acid benzyl ester

tert-butyl 4-{[(2R,3S)-3-{(1R)-1-{[tert-butyl-(dimethyl)-silyl]-oxy}-ethyl}-4-oxoazetidin-2-yl]-acetyl}-phenyl carbamate

(3S,4R)-3-((1R)-1-{[tert-butyl-(dimethyl)-silyl]-oxy}-ethyl)-4-[2-(3-{[tert-butyl-(dimethyl)-silyl]-oxy}-phenyl)-2-oxoethyl]-azetidin-2-one

(3S,4R)-4-[4-(allyloxycarbonyl)-1-benzyl-3-oxopiperidin-4-yl]-3-[(R)-1-(tert-butyldimethylsilyloxy)ethyl]-2-azetidinone

(5R,6S)-6-<(1R)-hydroxyethyl>-2-<(2R)-pyrrolidin-2-yl>-2-penem-3-carboxylic acid