| Summary: | Six phytotoxins were obtained from the culture filtrates of the ascomycete <i>Neofusicoccum batangarum</i>, the causal agent of the scabby canker of cactus pear (<i>Opuntia ficus-indica</i> L.) in minor Sicily islands. The phytotoxins were identified as (−)-(<i>R</i>)-mellein (<b>1</b>); (±)-botryoisocoumarin A (<b>2</b>); (−)-(3<i>R</i>,4<i>R</i>)- and (−)-(3<i>R</i>,4<i>S</i>)-4-hydroxymellein (<b>3</b> and <b>4</b>); (−)-terpestacin (<b>5</b>); and (+)-3,4-dihydro-4,5,8-trihydroxy-3-methylisocoumarin, which we named (+)-neoisocoumarin (<b>6</b>). This identification was done by comparing their spectral and optical data with those already reported in literature. The absolute configuration (3<i>R</i>,4<i>S</i>) to (+)-neoisocoumarin (<b>6</b>) was determined using the advanced Mosher method. All six metabolites were shown to have phytotoxicity on the host (cactus pear) and non-host (tomato) plants, and the most active compounds were (±)-botryoisocoumarin A (<b>2</b>), (−)-terpestacin (<b>5</b>), and (+)-neoisocoumarin (<b>6</b>).
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