Bioassay-Guided Isolation and Herbicidal Activity Evaluation of Phytochemicals from <i>Abelia grandiflora</i>

In response to the escalating challenges of weed resistance and environmental pollution, the discovery of novel herbicides derived from natural products provides a promising strategy to mitigate these dual challenges. In this study, we found that the ethanol crude extract of Abelia grandiflora (A. grandiflora) exhibits strong growth inhibitory activity against both monocotyledonous and dicotyledonous weeds, indicating its potential for the discovery of novel herbicidal compounds. Bioassay-guided fractionation led to the isolation and characterization of six compounds, including a new bis-iridoid glucoside, designated abelioside C (1), along with five known compounds: abelioside A (2), 7-O-acetyllaciniatoside V (3), daucosterol (4), isoboonein (5), and linarin (6). The structure of abelioside C was elucidated through comprehensive spectroscopic analyses, including 1D/2D NMR and HR-ESI-MS. Among them, abelioside A exhibited the strongest herbicidal activity, significantly inhibiting both root and shoot growth of Echinochloa crus-galli and Amaranthus retroflexus, with IC50 (half maximal inhibitory concentration) values ranging from 43.32 to 66.46 μg/mL. Both the ethanol extract and iridoid glucosides from A. grandiflora demonstrated significant herbicidal efficacy. These findings highlight A. grandiflora as a rich source of bioactive iridoid glucosides and support their potential for the development of sustainable and eco-friendly bioherbicides.