(3S,4R)-4-Allyl-3-[(R)-1-(tert-butyl-dimethyl-silanyloxy)-ethyl]-1-but-2-ynyl-azetidin-2-one

(3S,4R)-4-Allyl-1-[4-(tert-butyl-dimethyl-silanyloxy)-but-2-ynyl]-3-[(R)-1-(tert-butyl-dimethyl-silanyloxy)-ethyl]-azetidin-2-one

(3S,4R)-4-(but-3-enyl)-1-(tert-butyldimethylsilyl)-3-[(R)-1-tert-butyldimethylsilyloxyethyl]-2-azetidinone

[(2R,3S)-3-[(R)-1-(tert-Butyl-dimethyl-silanyloxy)-ethyl]-2-((S)-1-{1-[(E)-4-nitro-benzyloxycarbonylimino]-ethyl}-pyrrolidin-3-ylsulfanylcarbonylmethyl)-4-oxo-azetidin-1-yl]-oxo-acetic acid 4-nitro-benzyl ester