Methods of Synthesis for the Azolo[1,2,4]Triazines
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Methods of synthesis for the azolo[1,2,4]triazines Egor K. Voinkov1*, Roman A. Drokin1, Evgeny N. Ulomsky1,2, Oleg N. Chupakhin1,2, Valery N. Charushin1,2, Vladimir L. Rusinov1,2 1
Ural Federal University named after the first President of Russia B. N. Yeltsin, 19 Mira St., Yekaterinburg 620002, Russia; e-mail: [email protected] 2 Postovsky Institute of Organic Synthesis, Ural Branch of the Russian Academy of Sciences, 22 S. Kovalevskoi / 20 Akademicheskaya St., Yekaterinburg 620108, Russia
Translated from Khimiya Geterotsiklicheskikh Soedinenii, 2020, 56(10), 1254–1273
Submitted May 29, 2020 Accepted after revision July 9, 2020
The review summarizes and analyzes data from modern information sources on the methods of synthesis of azolo[X,Y-c][1,2,4]triazines. Approaches to the construction of the condensed azolotriazine heterocyclic system are considered and classified, the conditions of the synthetic processes, the structures and yields of the resulting products are given, and their biological action is described. Keywords: azolotriazines, pyrazoles, annulation, azo coupling, biological activity, cyclization, diazotization.
Azolo[X,Y-c][1,2,4]triazines are worthy representatives of the azoloazine series due to their structural similarity with known antiviral drugs (acyclovir, ganciclovir, abacavir, didanosine, entecavir, etc.), purine antimetabolites (mercaptopurine, fludarabine, nelarabine, pemetrexed) and many other drugs (azathioprine, allopurinol, etc.) included in the list of vital and essential drugs. Azolo[5,1-c][1,2,4]triazines represent a new family of antiviral drugs.1 The antiviral drug triazavirin (sodium salt of 3-nitro7-methylthio-1,2,4-triazolo[5,1-c][1,2,4]triazin-7-one, dihydrate) is currently successfully used in medical practice as a means for the treatment and prevention of influenza and acute respiratory viral infections,2–7 and is also effective against tick-borne encephalitis virus.8–11 The development and targeted synthesis of azolo[1,2,4]triazines remains highly relevant. In recent years, the number of publications on their synthesis has significantly increased, mainly related to the search for biologically active compounds with respect to known and new infectious agents. Hence, azolo[1,2,4]triazines are promising scaffolds for the formation of compounds with useful biological activity, which is revealed in this review. Methods for the synthesis of azolo[X,Y-c][1,2,4]triazines are basically reduced to two approaches: construction of the 1,2,4-triazine ring on the basis of azoles, or 0009-3122/20/56(10)-1254©2020 Springer Science+Business Media, LLC
annulation of the azole fragment to the 1,2,4-triazine ring. In the first case, most of the methods, which are the same for all types of diazoazoles, involve azo coupling of diazoazoles with CH-active two-carbon synthons according to the [4+2] principle. Therefore, in this review, the methods for the synthesis of azolo[X,Y-c][1,2,4]triazines obtained by azo coupling are classified mainly according to the CH-active two-carbon synthon, rega
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