(3S,4S)-4-<<4-<(1,1-dimethylethoxy)carbonyl>phenyl>oxy>-3-ethyl-3-butylazetidin-2-one

4-((2S,3S)-1-Benzylcarbamoyl-3-ethyl-4-oxo-3-propyl-azetidin-2-yloxy)-benzoic acid tert-butyl ester

4-((2S,3S)-3-Benzyl-1-benzylcarbamoyl-3-ethyl-4-oxo-azetidin-2-yloxy)-benzoic acid tert-butyl ester

4-[(2S,3S)-3-Benzyl-3-ethyl-4-oxo-1-((R)-1-phenyl-ethylcarbamoyl)-azetidin-2-yloxy]-benzoic acid

(2S,3S)-3-Benzyl-3-ethyl-2-[4-(4-methyl-piperazine-1-carbonyl)-phenoxy]-4-oxo-azetidine-1-carboxylic acid ((R)-1-phenyl-ethyl)-amide