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In terms of antibacterial action, this drug is analogous to other sulfanilamides; however, it possesses very prolonged action. Its half-life is from 120 to 200 h. Sulfadoxine is used for infectious diseases caused by microorganisms that are sensitive to the sulfanilamide drugs, such as infections of respiratory organs, gastric and urinary tracts; purulent infections of various localization, osteomyelitis, sinusitis, and other infections. It is used in combination with antimalarial drugs. Synonyms of this drug are sulfarmethoxine, fanasil, and fansidar.

Sulfalene: Sulfalene, 3-methoxy-2-sulfanilamidopyrazine (33.1.41), like other sulfanilamides, is synthesized by the standard scheme from 4-acetylaminobenzenesulfonyl chloride, which is reacted with 3-amino-2-methoxypyrazine, which is synthesized by two technologically available methods. The first of these methods consists of direct bromination of 2-amino-pyrazine using acetic acid as a solvent, which gives 3,5-dibromo-2-aminopyrazine (33.1.34). Reacting this with sodium methoxide gives 3-methoxy-5-bromo-2-aminopyrazine (33.1.35). Hydrogen reduction using a palladium on carbon catalyst replaces the bromine atom at C5 of the product with a hydrogen atom, giving 3-methoxy-2-aminopyrazine (33.1.36). This same 3-methoxy-2-aminopyrazine (33.1.36) is synthesized from 3-hydroxypyrazin-

2-carboxamide. Reacting this with phosphorous oxychloride replaces the hydroxyl group with a chlorine atom while the carboxamide group simultaneously undergoes dehydration to form 3-chloro-2-cyanopyrazine (33.1.37). Next, reacting this with sodium methoxide gives 3-methoxy-2-cyanopyrazine (33.1.38). The cyano group in this compound is hydrolyzed by a base in the presence of hydrogen peroxide to a carboxamide group, giving

3-methoxy-2-carboxamideopyrazine (33.1.39). The resulting product undergoes a Hofmann rearrangement when reacted with sodium hypochlorite, giving the desired 3-methoxy-2 aminopyrazine (33.1.36). Reacting this with 4-acetylaminobenzenesulfonyl chloride and subsequent hydrolysis of the acetyl group with a base to (33.1.40) gives sulfalene [32-34].

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