The molecule is an erythromycin cation that is the conjugate acid of erythromycin B, arising from protonation of the tertiary amino group on the 3,4,6-trideoxy-3-(dimethylamino)-beta-D-xylo-hexopyranosyl residue; major species at pH 7.3.
[(2S,3R,4S,6R)-2-[[(3R,4S,5S,6R,7R,9R,11R,12S,13R,14R)-14-ethyl-7,12-dihydroxy-4-[(2R,4R,5S,6S)-5-hydroxy-4-methoxy-4,6-dimethyloxan-2-yl]oxy-3,5,7,9,11,13-hexamethyl-2,10-dioxo-oxacyclotetradec-6-yl]oxy]-3-hydroxy-6-methyloxan-4-yl]-dimethylazanium