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(2007/10/02)p-nitrobenzyl hydroxy-(2-iodomethyl-4-oxoazetidin-1-yl)acetate
p-nitrobenzyl isopenam-3-endo-carboxylate
p-nitrobenzyl isopenam-3-exo-carboxylate
Chloro-(2-iodomethyl-4-oxo-azetidin-1-yl)-acetic acid 4-nitro-benzyl ester
3-exo-p-nitrobenzyloxycarbonylisopenam 2,2-dioxide