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

A new tetrasubstituted octanoic acid, named hyfraxinic acid (), was isolated together with known 1-deoxyviridiol (), viridiol (), nodulisporiviridin M (), and demethoxyviridiol () from the organic extract of responsible for ash ( L.) dieback in Europe. Hyfraxinic acid () 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 (3) of 1-deoxyviridiol. Nodulisporiviridin M () was isolated for the first time from . The phytotoxicity of each compound was tested by a leaf puncture assay on L., L., L., L., and L. leaves. Compounds , , and exhibited remarkable phytotoxicity on all plants tested, inducing necrotic lesions at concentrations of 1.0 and 0.5 mg/mL, while compounds and were found to be inactive in this bioassay. These results could contribute to a deeper understanding of the pathogenicity of .