Pièce de Self-Résistance: a New Paradigm for Natural-Product Herbicide Discovery

Laboratory bioassay, greenhouse experiment and 3D-QSAR studies on berberine analogues: a search for new herbicides based on natural products

BACKGROUND

Berberine is a herbicidal chemical that we isolated from Coptis chinensis. In continuation of our program aimed at discovering and developing natural botanical herbicides, we evaluated the herbicidal activities of 39 berberine analogues and developed a three-dimensional quantitative structure-activity relationship (3D-QSAR) model.

RESULTS

Among these 39 analogs, the most active compounds were determined to be worenine chloride and coptisine chloride, with median inhibitory concentration (IC₅₀ ) values on all eight tested weed species of < 10 mg L^-1 . As a reference, the IC₅₀ values of berberine on six weed species were < 10 mg L^-1 . Furthermore, the results of a greenhouse experiment showed that at 10 mg L^-1 , and 7 days after treatment, the effects of worenine chloride and coptisine chloride on Lemna minor and Ageratum conyzoides were significantly higher than those of glyphosate and sulcotrione. In the 3D-QSAR analysis, the electrostatic field contour map indicated that introducing an electropositive group in the N-7, C-9 and C-10 positions would potentially improve the inhibition rate. A positively charged nitrogen atom at the N-7 position was important for activity. Replacement of -OCH₃ by -OH at the C-9 and C-10 positions could decrease the inhibitory activity, while the hydrophobic field contour map revealed that the hydrophobicity of the C-10 position was associated with high activity. Moreover, the hydrogen bond acceptor field contour map suggested that the existence of a hydrogen bond acceptor at the C-3 and C-9 positions might affect the inhibition rate.

CONCLUSIONS

3D-QSAR provided meaningful clues to the structural features of berberine analogues that will assist the design of more potent herbicidal compounds in the future. © 2020 Society of Chemical Industry.

Reconsidering Hydrosols as Main Products of Aromatic Plants Manufactory: The Lavandin (Lavandula intermedia) Case Study in Tuscany

: The present work evaluates for the first time two Lavandin (Lavandula × intermedia Emeric ex Loisel.) aromatic waters obtained from different plant organs, the flowers and the stems. Both extracts were analysed by GC-MS, which indicates semi-quantitative differences between the major metabolites including linalool, 1,8-cineole, camphor, linalyl acetate and 4-terpineol. ¹H-NMR and LC-MS investigation confirmed the presence of these compounds. Moreover, behavioural tests with the food insect pest Tribolium confusum (Coleoptera Tenebrionidae) showed a good repellency for both hydrosols extracts with RD₅₀ values of 3.6 and 3.3 µL cm^-2 for the flowers and stems, respectively; at the higher concentrations, however, the hydrosol extract from the flowers is expected to be more effective than the one from the stems. The effect of the flowers and stems aromatic water of Lavandin on seed germination of Raphanus sativus was also evaluated. Results showed that seed germination was completely inhibited by flowers hydrolate, having a possible application as natural herbicide. The overall experience with these Lavandin extracts indicates the potential of improved hydrolates to become the main distillation products, rather than by-products, of the aromatic plants manufacturing; this stimulates further discussions about the potential positive impacts that such a shift could have in the context of ecopharmacognosy.