Azithromycin imp. I

Azithromycin imp. I is a synthetic byproduct arising from incomplete glycosylation during Azithromycin production, characterized by a 15-membered macrolactone core lacking the cladinose sugar moiety. It retains the desosamine amino sugar and the 9α-hydroxy-9α-methyl substituent critical to the parent drug's structure. The absence of cladinose introduces a free 3-hydroxyl group on the lactone ring, distinguishing it from Azithromycin. This impurity is utilized as an HPLC reference standard for quantifying process-related impurities in Azithromycin active pharmaceutical ingredients.