33396-29-1 8,9-Didehydro-9-deoxo-6-deoxy-6,9-epoxyerythromycin De-(N-methyl)-N-ethyl-8,9-anhydroerythromycin A 6,9-hemiacetal EM 523 EM-523 EM523L Erythromycin, 8,9-didehydro-9-deoxo-6-deoxy-6,9-epoxy- N-Ethyl-N-demethyl-8,9-anhydroerythromycin A 6,9-hemiketal