Fused systems combining 1,2,4-triazole and 1,3,4-thiadiazole rings occupy a prominent place in modern bioorganic and medicinal chemistry due to the diverse range of their biological activities. Thus, compounds incorporating [1,2,4]triazolo[3,4-b]thiadiazole ring system are of essential importance and particular interest both in the pharmaceutical as well as agrochemical industries. Herein, an overview of certain synthetic methodologies for obtaining of heterocyclic compounds based on functionally substituted 1,2,4-triazolo[3,4-b][1,3,4]thiadiazoles are presented.

Condensed bicyclic systems with thiadiazole core being annelated to other five-membered heterocycles such as 1,3-thiazole, imidazole or 1,2,4-triazole occupy prominent place in medicinal chemistry because of their broad spectrum of pharmacological activities. The combination of several heterocycles into a bicyclic system commonly provides much more interest in the enhanced activity profile of its analogs than their parent separate constituents. In this review, we summarized the literature data about the main approaches for obtaining and possible directions of structural modification of the most common 1,3,4-thiadiazole containing [5+5] annelated heterosystems as promising objects for modern medicinal chemistry.