Antifungal Polyacetylenic Deoxyglycosides Isolated from Endophytic Fungus Xylaria sp. VDL4 Associated with Vaccinium dunalianum

One novel C₁₀ polyacetylene rhamnoside, 4,6,8-decatriyne-1-<i>O</i>-α-L-rhamnopyranoside, named xylariside A (<b>1</b>), together with two novel C₁₀ polyacetylene quinovopyranosides, 4,6,8-decatriyne-1-<i>O</i>-α-D-quinovopyranoside, xylariside B (<b>2</b>), and 8<i>E</i>-decaene-4,6-diyne-1-<i>O</i>-α-D-quinovopyranoside, xylariside C (<b>3</b>), were obtained from the solid fermentation of <i>Xylaria</i> sp. VDL4, an endophytic fungus isolated from <i>Vaccinium dunalianum</i> wight (Ericaceae). Their chemical structures were elucidated through a combination of spectroscopic techniques. The antifungal activities of these compounds were evaluated in vitro against four phytopathogenic fungi (<i>Fusarium oxysporum</i>, <i>Botrytis cinerea</i>, <i>Phytophthora capsici</i>, and <i>Fusarium solani</i>). Compound <b>2</b> demonstrated significant antifungal activities, with minimum inhibitory concentration (MIC) values ranging from 3.91 to 7.81 μg/mL. Compound <b>2</b>'s effectiveness levels were similar to those of the reference drugs thiabendazole and carbendazim (each MIC = 0.98-15.62 μg/mL). Xylariside B (<b>2</b>) was further evaluated against <i>B. cinerea</i> in vivo. It exhibited remarkable efficacy in both the prevention and treatment of tomato and strawberry gray mold. Molecular docking studies confirmed the antifungal mechanism of compound <b>2</b> by revealing its binding interactions with key enzyme targets in <i>B. cinerea</i>, thereby supporting the observed in vitro and in vivo results. Additionally, compound <b>2</b> showed effective inhibition of α-glucosidase, with IC₅₀ values of 5.27 ± 0.0125 μg/mL.