Stereochemical studies of tetracycline antibiotics and their common impurities by 400 MHz 1 H NMR spectroscopy

The 400 MHz 1 H NMR spectra of hydrochlorides of tetracycline, chlortetracycline, doxycycline and two epimeric derivatives are reported and interpreted in terms of solute conformation in DMSO‐ d 6 and configuration. Coupling constant magnitudes within the system H‐5, H‐4a, H‐4 and H‐12a and dimethylamino chemical shifts are applied to the configurational assignment of isomeric α‐ and β‐apooxytetracyclines.