- Manufacture of 6-methylenetetracyclines
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Methacycline (6-methylene-5-oxytetracycline) is prepared by halogenating oxytetracycline (5-hydroxytetracycline) to produce the 11a-halo-6,12-hemiketal, under conditions which form and maintain the product in the enolic form, reacting the hemiketal base with acid to produce the hemiketal acid salt, dehydrating the acid salt to form 11a-halo-6-methylene-5-oxytetracycline, and reducing the compound to the salt of 6-methylene-5-oxytetracycline. An improved method for producing the 6-methylenetetracycline base from the product salt is also disclosed. The process is applicable to the synthesis of 6-methylenetetracycline per se or other 6-methylenetetracyclines, as well as methacycline.
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