The molecule is an erythromycin cation resulting from the protonation of the tertiary amino group of erythromycin D; the major species at pH 7.3. It is a conjugate acid of an erythromycin D.
[(2S,3R,4S,6R)-2-[[(3R,4S,5S,6R,7R,9R,11R,12S,13R,14R)-4-[(2R,4R,5S,6S)-4,5-dihydroxy-4,6-dimethyloxan-2-yl]oxy-14-ethyl-7,12-dihydroxy-3,5,7,9,11,13-hexamethyl-2,10-dioxo-oxacyclotetradec-6-yl]oxy]-3-hydroxy-6-methyloxan-4-yl]-dimethylazanium