methyl 2-((2R,3R)-2-(acetylthio)-3-methoxy-4-oxo-3-(2-phenoxyacetamido)azetidin-1-yl)-2-(triphenyl-l⁵-phosphanylidene)acetate

methyl 2-((2R,3S)-2-(acetylthio)-4-oxo-3-(2-phenylacetamido)azetidin-1-yl)-2-hydroxyacetate

methyl 2-((2R,3S)-2-(acetylthio)-4-oxo-3-(2-phenylacetamido)azetidin-1-yl)-3-methylbut-2-enoate

methyl α-(4R-acetylthio-3S-methoxy-3-phenoxyacetamido-2-azetidinon-1-yl)-β-methylcrotonate