(3S,4R)-3-[(R)-1-(tert-Butyl-dimethyl-silanyloxy)-ethyl]-4-((S)-1-methyl-2-trityloxymethyl-allyl)-azetidin-2-one

(1S,6S,8aS,8bR)-1-[(R)-1-(tert-Butyl-dimethyl-silanyloxy)-ethyl]-6-(2-methoxy-ethyl)-2-oxo-1,2,5,6,7,8,8a,8b-octahydro-azeto[2,1-a]isoindole-4-carboxylic acid benzyl ester

(5R,6S)-3-tert-Butyl-6-((R)-1-hydroxy-ethyl)-7-oxo-4-thia-1-aza-bicyclo[3.2.0]hept-2-ene-2-carboxylic acid 4-nitro-benzyl ester

<3S-<3α(S*),4β>>-methyl 3-(1-t-butyldimethylsilyloxyethyl)-2-azetidinone-4-carboxylate

2-{(2R,3S)-3-[(R)-1-(tert-Butyl-dimethyl-silanyloxy)-ethyl]-4-oxo-azetidin-2-yl}-3,4-dihydro-2H-acridin-1-one