Azole

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Azoles are a family of five-membered rings that include nitrogen and at least one other non-carbon atom (such as nitrogen, sulfur, or oxygen) in the ring. They’re named using the Hantzsch–Widman system. The parent rings are aromatic with two double bonds; there are simpler forms called azolines and azolidines with fewer double bonds. In azoles, exactly one lone pair from each heteroatom helps form the aromatic ring. When these rings are reduced, the prefix is kept (for example, pyrazoline and pyrazolidine). Ring numbering starts at the heteroatom that is not part of a double bond and goes toward the other heteroatom. Imidazole and other five-membered rings with two nitrogens are common in nature and are key parts of many biomolecules, such as histidine.

In antifungals, ketoconazole was the first azole taken orally for systemic fungal infections in the early 1980s. This was followed by triazoles like fluconazole and itraconazole, which have broader activity and better safety. To address limitations in activity, drug interactions, toxicity, resistance, and pharmacokinetics, newer azoles were developed. Second-generation triazoles—voriconazole, posaconazole, ravuconazole—are more potent and effective against resistant fungi. For wood preservation, other azoles such as propiconazole, tebuconazole, and cyproconazole are used to protect wood from rot, sometimes with copper compounds. These azoles work well in solvents and water-based formulations and are effective against wood-destroying fungi.