LAUSR

A new tetrasubstituted octanoic acid, named hyfraxinic acid (1), was isolated together with the 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's 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 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.