| Summary: | <i>Fusarium</i> is one of the most toxigenic phytopathogens causing diseases and reduced agricultural productivity worldwide. Current chemical fungicides exhibit toxicity against non-target organisms, triggering negative environmental impact, and are a danger to consumers. In order to explore the chemical diversity of plants for potential antifungal applications, crude extract and fractions from <i>Monotes kerstingii</i> were screened for their activity against two multi-resistant <i>Fusarium oxysporum</i> strains: <i>Fo32931</i> and <i>Fo4287</i>. Antifungal activity was evaluated by the determination of minimum inhibitory concentration (MIC) by broth dilution of fermentative yeasts using kinetic OD<sub>600 nm</sub> reading by a spectrophotometer. The <i>n</i>-butanol fraction showed the best activity against <i>Fo4287</i>. We screened eleven previously reported natural compounds isolated from different fractions, and a stilbene–coumarin 5-[(1<i>E</i>)-2-(4-hydroxyphenyl)ethenyl]-4,7-dimethoxy-3-methyl-2<i>H</i>-1-benzopyran-2-one (<b>1</b>) was the most active compound against both strains. Compound <b>1</b> was employed as a nucleophile with a selection of electrophilic derivatizing agents to synthesize five novel stilbene–coumarin analogues. These semisynthetic derivatives showed moderate activity against <i>Fo32931</i> with only prenylated derivative exhibiting activity comparable to the natural stilbene–coumarin (<b>1</b>), demonstrating the key role of the phenolic group.
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