Indazole - an emerging privileged scaffold: synthesis and its biological significance

Nitrogen-containing molecules are an important class of heterocyclic compounds. Among these, indazole is one of the most important scaffolds with a broad scope because of its pharmaceutical and biological properties. Many novel molecules were reported in clinical trials for treating various diseases containing the indazole scaffold. Indazole has a vast potential for the discovery of novel pharmaceuticals such as anti-bacterial, anti-fungal, anti-leishmanial, antidiabetic, anti-cancer, anti-tuberculosis, anti-Parkinson's, anti-protozoal, anti-depressant, and anti-inflammatory. This review covers the structures of new indazoles, the current pipeline of indazole-containing compounds in the various stages of clinical trials, and naturally occurring indazoles, along with some marketed drugs. Furthermore, we have covered the different methods for the synthesis of 1H-indazole, 2H-indazole, and 3H-indazole with a wide variety of starting materials under different reaction conditions and their biological activities.