Antifungal activity and tautomeric cyclization equilibria of formylphenylboronic acids

[Display omitted] •2-Formylphenylboronic acids display antifungal activity.•It is due to their tautomerization to the corresponding 3-hydroxybenzoxaboroles. 2-Formylphenylboronic acid and four isomeric fluoro-2-formylphenylboronic acids have been found active against a series of fungal strains: Aspergillus, Fusarium, Penicillium and Candida. The level of antifungal activity was evaluated by agar diffusion tests as well as the determination of minimum inhibitory concentrations (MICs) by serial dilution method. Among the tested compounds, 4-fluoro-2-formylphenylboronic acid – an analogue of the known antifungal drug Tavaborole (AN2690) – proved to be the most potent antifungal agent. The tautomeric equilibrium leading to the formation of 3-hydroxybenzoxaboroles as well as the position of the fluorine substituent were revealed to play a crucial role in the observed activity.