Hyfraxinic Acid, a Phytotoxic Tetrasubstituted Octanoic Acid, Produced by the Ash (Fraxinus excelsior L.) Pathogen Hymenoscyphus fraxineus Together with Viridiol and Some of Its Analogues

• Published in: Journal of agricultural and food chemistry Vol. 67; no. 49; pp. 13617 - 13623
• Main Authors: Masi, Marco, Di Lecce, Roberta, Tuzi, Angela, Linaldeddu, Benedetto Teodoro, Montecchio, Lucio, Maddau, Lucia, Evidente, Antonio
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 11-12-2019
• Subjects: Androstenediols - chemistry; Androstenediols - metabolism; Androstenediols - toxicity; Ascomycota - metabolism; Ascomycota - pathogenicity; Caprylates - chemistry; Caprylates - metabolism; Caprylates - toxicity; Fraxinus - microbiology; Juglans - drug effects; Molecular Structure; Plant Diseases - microbiology; Quercus - drug effects; Virulence; phytotoxins; demethoxyviridiol; Hymenoscyphus fraxineus; viridiol; ash dieback; hyfraxinic acid
• ISSN: 0021-8561; 1520-5118
• DOI: 10.1021/acs.jafc.9b06055

A new tetrasubstituted octanoic acid, named hyfraxinic acid (1), was isolated together with known 1-deoxyviridiol (2), viridiol (3), nodulisporiviridin M (4), and demethoxyviridiol (5) from the organic extract of Hymenoscyphus fraxineus responsible for ash (Fraxinus excelsior L.) dieback in Europe. Hyfraxinic acid (1) was characterized, using spectroscopic methods, as 2,4-dihydroxy-7-methyl-6-methyleneoctanoic acid. Furthermore, the advanced Mosher method was used to determine the absolute configuration (3R) of 1-deoxyviridiol. Nodulisporiviridin M (4) was isolated for the first time from H. fraxineus. The phytotoxicity of each compound was tested by a leaf puncture assay on Celtis australis L., Quercus suber L., Hedera elix L., Juglans regia L., and Fraxinus angustifolia L. leaves. Compounds 1, 3, and 5 exhibited remarkable phytotoxicity on all plants tested, inducing necrotic lesions at concentrations of 1.0 and 0.5 mg/mL, while compounds 2 and 4 were found to be inactive in this bioassay. These results could contribute to a deeper understanding of the pathogenicity of H. fraxineus.