4-Epi Doxycycline (Crude)

4-Epi Doxycycline is a stereoisomeric impurity arising from inversion of the 4-hydroxyl configuration in the tetracycline core of doxycycline. It retains the characteristic dimethylamino group at position 4, 6-keto, and 10β-hydroxyl functionalities but exhibits altered conformational flexibility due to the epimerized hydroxyl at C-4. This structural deviation reduces chelation efficiency with divalent cations compared to the parent compound. Synthesized as a minor byproduct during doxycycline fermentation or semi-synthetic derivatization. Serves as a reference standard for HPLC-based quantification of epimeric impurities in doxycycline APIs.