Herbicidal and Antibacterial Secondary Metabolites Isolated from the Nicotiana tabacum-Derived Endophytic Fungus Aspergillus japonicus TE-739D

Endophytic fungi possess a unique ability to produce abundant secondary metabolites, which play an active role in the growth and development of host plants. In this study, chemical investigations on the endophytic fungus <i>Aspergillus japonicus</i> TE-739D derived from the cultivated tobacco (<i>Nicotiana tabacum</i> L.) afforded two new polyketide derivatives, namely japoniones A (<b>1</b>) and B (<b>2</b>), as well as four previously reported compounds <b>3</b>-<b>6</b>. Their chemical structures were elucidated by detailed spectroscopic analyses and quantum chemical calculations. In the herbicidal assays on the germination and radicle growth of <i>Amaranthus retroflexus</i> L. and <i>Eleusine indica</i> seeds, compound <b>1</b> was found to inhibit the germ and radicle elongation. Notably, compound <b>2</b> showed potent herbicidal activity against <i>A. retroflexus</i> L. germ elongation, with an IC₅₀ value of 43.6 μg/mL, even higher than the positive control glyphosate (IC₅₀ = 76.0 μg/mL). Moreover, compound <b>4</b> demonstrated strong antibacterial effects against the pathogens <i>Bacillus cereus</i> and <i>Bacillus subtilis</i>, with a comparable MIC value of 16 μg/mL to the positive control chloramphenicol. These findings indicate that the endophytic fungus <i>A. japonicus</i> TE-739D holds significant metabolic potential to produce bioactive secondary metabolites, which are beneficial, providing survival value to the host plants.