Methacycline is used for the same indications as other antibiotics of the tetracycline series. In some cases it is tolerated better than tetracyclines. Synonyms of this drug are ron-domycin, methamycin, adramycin, and others.

Doxycycline: Doxycycline, 4-dimethylamino-1,4,4a,5,5a,6,11,12a-oxtahydro-3,5,10,12, 12a-pentahydroxy-6-methyl-1,11-dioxo-2,naphthacencarboxamide (32.3.7), is an isomer of tetracycline that differs only in the placement of one hydroxyl group. Doxycycline can be formally viewed as the result of transferring the C6 hydroxyl group of tetracycline to C5. Doxycycline is synthesized in two different ways from oxytetracycline (32.3.2). One of the ways suggests dehydrating oxytetracycline at C6 by reducing the tertiary hydroxyl group with hydrogen using a rhodium on carbon catalyst [226,227].

The second way is analogous to that of giving methacycline, which suggests an oxidation stage of the homoallyl system, except that N-chlorosuccinimide is used as the oxidant, which results in the formation of a naphthacentetrahydrofuran derivative (32.3.8), and which upon being reacted with hydrofluoric acid breaks apart to form an 11a-chloro-6-exomethylene derivative (32.3.9). Reductive dechlorination of this product using sodium thiosulfate forms the intermediate methacycline (32.3.6), and thiophenol is joined to the methyl group that carry out radical reactions, forming the derivative (32.3.10). This product is reduced by hydrogen over a Raney nickel catalyst, during which reductive desulfu-rization takes places, giving doxycycline [225,228-230].

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