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Fexinidazole is a medication used in the treatment of African trypanosomiasis caused by trypanosoma brucei gambiense. An antitrypanosomal agent. It also functions as a medication used against the main species that cause visceral and cutaneous new World leishmaniasis.

Fexinidazole is a 2-substituted-5-nitroimidazole antiparasitic drug originally synthesised and disclosed in the 1970s by Hoechst AG (now part of Sanofi). The drug was found to be active against Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense (African trypanosomes) through a joint screening campaign by the Drugs for Neglected Diseases initiative and Sanofi in 2005. This has led to the rediscovery of fexinidazole as a candidate for the treatment of human African trypanosomiasis (HAT, commonly known as sleeping sickness.) In November 2018, the European Medicines Agency (EMA) gave a positive opinion on fexinidazole for the treatment of stage 1 (haemolymphatic) and stage 2 (meningoencephalitic) HAT in adults and children. As the first all-oral treatment for HAT, the World Health Organisation (WHO) added it to its list of essential medicines in 2019.In July 2021, the US FDA approved fexinidazole for the treatment of HAT in patients aged 6 years and older who weigh at least 20kg.

Anti TrypanosomaLeishmania agent.''Fexinidazole is a potent anti-Trypanosoma agent. Trypanosoma species human protozoan pathogens are responsible for sleeping sickness and Chagas disease. In vivofexinidazole is oxidized to sulfoxide and sulfone metabolites th at are effective in blocking the progression of the parasitic disease visceral leishmaniasis. The mechanism of action appears to be by reductive activation via an NADH-dependent nitroreductase expressed by the parasites.

The synthesis of Fexinidazole started with the methylation of nitroimidazole (2.1) using dimethyl sulphate in dioxane to give intermediate 2.2 in 82% yield. The methylated imidazole 2.2 was subsequently reacted with formaldehyde in dimethyl sulfoxide to produce the corresponding imidazolyl methanol derivative 2.3 in 62% yield. Intermediate 2.3 was reacted with dichlorosulfoxide in chloroform to give the corresponding 2-chloromethyl-1-methyl-5-nitroimidazole 2.4, which was then coupled with 4-methylmercaptophenol (2.5) in the presence of acetone and potassium carbonate to produce "wet" fexinidazole hydrochloride (2.6). The final free base of fexinidazole (2) was obtained by neutralisation with 25% aqueous ammonia solution, giving an overall yield of 65% for the entire three-step reaction.

Trypanosoma

[1] Bioorganic and Medicinal Chemistry Letters, 2011, vol. 21, # 3, p. 1015 - 1018