Biological transformation of anhydrotetracyclines to 6-deoxytetracyclines
alpha.-6-Deoxy-5-hydroxytetracycline (doxycycline) is obtained by adding, at the beginning or during aerobic fermn., anhydro-5-hydroxytetracycline to a culture of Streptomyces alboflavus (NCIB 10588 or NCIB 10589) in an aq. medium. After the transformation is complete, the fermented broth is acidified to pH 0.1-1.5 and the doxycycline sepd. by forming insol. derivs. with 3-hydroxy-2-naphthylates or with methylene-5,5-disalicylates. The crude ppt. is purified by transformation into the derivs. of .alpha.-6-deoxytetracycline with a purity sufficient for therapeutical use.