127020-81-9 2-Azetidinecarboxylic acid, 3-ethyl-1-((4-nitrophenyl)sulfonyl)-4-oxo-, ethyl ester, trans- L 652,117 L 652,306 L 652117 L 652306 L-652117 L-652306 cis-4-Ethoxycarbonyl-3-ethyl-1-(4-nitrophenylsulfonyl)-azetidin-3-one