Phytotoxic Metabolites from Three Neofusicoccum Species Causal Agents of Botryosphaeria Dieback in Australia, Luteopyroxin, Neoanthraquinone, and Luteoxepinone, a Disubstituted Furo-α-pyrone, a Hexasubstituted Anthraquinone, and a Trisubstituted Oxepi-2-one from Neofusicoccum luteum.

Abstract

Different phytotoxic metabolites were isolated from the organic extract of Neofusicoccum luteum, Neofusicoccum australe, and Neofusicoccum parvum, causal agents of Botryosphaeria dieback in Australia. N. luteum produced a new disubstituted furo-α-pyrone, a hexasubstituted anthraquinone, and a trisubstituted oxepi-2(7H)-one, luteopyroxin (4), neoanthraquinone (5), and luteoxepinone (7), respectively, together with the known (±)-nigrosporione (6), tyrosol (8), (R)-(-)-mellein (1), and (3R,4S)-(-)- and (3R,4R)-(-)-4-hydroxymellein (2 and 3). The three melleins and tyrosol were also produced by N. parvum, while N. australe produced (R)-(-)-mellein (1), neoanthraquinone (5), tyrosol (8), and p-cresol (9). Luteopryoxin (4), neoanthraquinone (5), and luteoxepinone (7) were characterized by analyses of physical data, essentially one- and two-dimensional nuclear magnetic resonance and high-resolution electrospray ionization mass spectrometry. The relative and absolute configurations of luteopyroxin (4) were determined by nuclear Overhauser effect spectroscopy and experimental and calculated electronic circular dichroism data. When assayed on grapevine leaves, neoanthraquinone (5) showed the highest toxic effect, causing severe shriveling and withering. Luteopyroxin (4), nigrosporione (6), and luteoxepinone (7) also showed different degrees of toxicity, while p-cresol (9) displayed low phytotoxicity.