Structure-activity relationships of cadinane-type sesquiterpene derivatives against wood-decay fungi

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Abstract
Cadinane-type sesquiterpenes have a wide spectrum of biological activity, but their use as wood preservatives and the structure-activity relationships of their derivatives have not yet been reported. A total of 13 compounds were synthesized from T-cadinol, T-muurolol, and α-cadinol and their chemical structures were confirmed by IR, MS, and 1H and 13C NMR. The antifungal properties of 16 compounds against three wood-decay fungi were evaluated in vitro. α-Cadinol showed strong antifungal activity against Lenzites betulina, Trametes versicolor, and Laetiporus sulphureus (total mean IC50 0.10 mM). Among the derivatives synthesized, 3β-ethoxy-T-muurolol (0.24 mM), 4ξH-cadinan-10β-ol (0.25 mM), 4ξH-muurolan-10β-ol (0.29 mM), and 4ξH-cadinan-10α-ol (0.25 mM) showed good antifungal activity against all fungi tested. Correlation was observed between the antifungal activity of the compounds tested and log P. Furthermore, the presence of an unsaturated double bond and oxygen-containing functional groups in the compounds plays a key role in their antifungal activity. The stereo configuration of cadinane-type sesquiterpenes also influences their antifungal activity. Understanding how the structure of natural compounds relates to their antifungal function is important and may facilitate their application as novel wood preservatives.