New α-pyrone derivatives with herbicidal activity from the endophytic fungus Alternaria brassicicola

Three pairs of undescribed enantiomeric α-pyrone derivatives (1a/1b–3a/3b) and six previously undescribed congeners (4–9), were obtained from the fungus Alternaria brassicicola, which was isolated from the fresh leaves of Siegesbeckia pubescens Makino (Compositae). The structures of these new compounds were identified by extensive NMR spectroscopic and HRESIMS data, and their absolute configurations were further elucidated by ECD calculations, a modified Mosher's method, and single-crystal X-ray diffraction. This is the first report of three pairs of enantiomeric α-pyrone derivatives from fungus Alternaria brassicicola, and these enantiomers were successfully acquired from scalemic mixtures via chiral HPLC. Compounds 1a/1b–3a/3b and 4–9 were evaluated for the herbicidal activity against Echinochloa crusgalli, Setaria viridis, Portulaca oleracea and Taraxacum mongolicum. At a concentration of 100 μg/mL, compounds 1a and 1b could significantly inhibit the germination of the monocotyledon weed seeds (E. crusgalli and S. viridis) with inhibitory ratios ranging from 68.6 ± 6.4% to 84.2 ± 5.1%, , which was equivalent to that of the positive control (glyphosate). In addition, the structure-herbicidal activity relationship of the above compounds was discussed. To a certain extent, the results of this study will attract great interest for the potential practical application of promising fungal metabolites, α-pyrone derivatives, as ecofriendly herbicides. [Display omitted] •Twelve new bioactive metabolites were isolated from the fungus Alternaria brassicicola.•Their absolute configurations were characterized by a modified Mosher's method, chemical conversion, X-ray crystallography analysis, and ECD calculations.•Compounds 1a/1b–3a/3b are the first examples of enantiomeric α-pyrone derivatives from the fungus A. brassicicola.•Compounds 1a and 1b could significantly inhibit the germination of the monocotyledon weed seeds (E. crusgalli and S. viridis), which was equivalent to that of the positive control (glyphosate). Three pairs of undescribed enantiomeric α-pyrone derivatives (1a/1b–3a/3b) and six undescribed congeners (4–9), were obtained from the fungus Alternaria brassicicola that was isolated from the fresh leaves of Siegesbeckia pubescens Makino (Compositae). The structures of these new compounds were characterized by extensive NMR spectroscopic and HRESIMS data, and their absolute configurations were further elucidated by a modified Mosher's method, chemical co