Azolo[5,1 c] 1,2,4 triazines as a new class of antiviral compoundsSynthetic methods, reactivity, and the properties of a new class of antiviral compounds, pyrazolo , imidazo , 1,2,4 triazolo[5,1 c] 1,2,4 triazinones, tetrazolo[5,1 b] 1,2,4 triazinones, and azoloannulated amino 1,2,4 triazines having structural similarity with biogenic purines and capable of mimicking them in metabolic processes are considered.Aza analogs and structural analogs of natural purine and pyrimidine bases are widely employed for the synthesis of abnormal nucleosides in the search for antiviral and antitumor agents. Abnormal nucleosides on the basis of azauracil, azathymine, and azacytosine have been prepared, 18-31 for example, antiviral compounds 6-9. Pyrrolo , 32 imidazo , 33-35 and 1,2,4 triazolo 1,2,4 tri azines 33,36,37 containing a ribosyl fragment in the azole ring, for example, compounds 10-12, have been described.This review considers the synthetic methods, reactiv ity, and properties of 1,2,4 triazinones annulated at the edge to pyrrole, pyrazole, imidazole, or 1,2,4 triazole frag ment; 7 aminoazolo 1,2,4 triazines and tetrazolo[5,1 b] 1,2,4 triazine 7(4H) ones, 7 aminotetrazolo[5,1 b] 1,2,4 triazines, and abnormal nucleosides based on them. The last section is devoted to the antiviral action of this class of compounds, which allows one to estimate the synthetic potential of the heterocyclic system in the search for anti viral agents.The considered azolotriazines have three types of num bering of the heterocyclic system. Thus the numbering of pyrrolo , pyrazolo , imidazo[5,1 c] 1,2,4 triazine, and imidazo[2,1 c] 1,2,4 triazine I starts with a triazine ni trogen, while in 1,2,4 triazolo[3,4 c] 1,2,4 triazine II, 1,2,3 triazolo , 1,2,4 triazolo , and tetrazolo[5,1 c] 1,2,4 triazines III, from azole nitrogens.Discussion of the methods of synthesis and chemical properties of the whole group of azolo[c] 1,2,4 triazines using their inherent numbering systems is inconvenient for the unified information perception; therefore, in the review we number the heterocyclic system as is usually done for 1,2,3 triazolo , 1,2,4 triazolo , and tetrazolo [5,1 c] 1,2,4 triazines III.
Synthesis of azolo[5,1 c] 1,2,4 triazin 7(4H) ones and 7 aminoazolo[5,1 c] 1,2,4 triazinesThe azolo[5,1 c] 1,2,4 triazine system can be con structed by two strategic approaches: annulation of a 1,2,4 triazine ring to an azole ring or annulation of an azole ring to a 1,2,4 triazine ring. The annulation of a 1,2,4 triazine ring is mainly performed according to the [4+2] pattern, the N-C-N-N fragment of the 1,2,4 triazine ring be ing provided by the azole moiety, and the C-C fragment coming from the second reactant. According to the [3+3]Azolo[5.1 c] 1,2,4 triazine Russ.
