Synthetic approaches to 1,2,4-triazolo[5,1-c][1,2,4]triazin-7-ones as basic heterocyclic structures of the antiviral drug Riamilovir (“Triazavirin®”) active against SARS-CoV-2 (COVID-19)

ABSTRACT
Fragments of 1,2,4-triazolo[5,1-c][1,2,4]triazin-7-one are found in many compounds with various types of biological activities, including the antiviral drug Riamilovir (Triazavirin®), which shows activity against SARS-CoV-2 (COVID-19). Therefore, the development of convenient methods for the synthesis of new derivatives of 1,2,4-triazolo[5,1-c][1,2,4]triazin-7-one is always in demand. This review systematizes the information on the most common synthetic methods for constructing the 1,2,4-triazolo[5,1-c][1,2,4]triazin-7-one heterocyclic system.