Comparative SAR Evaluations of Annonaceous Acetogenins for Pesticidal Activity

The activities of 44 Annonaceous acetogenins, which were originally isolated by monitoring plant fractionations with the brine shrimp lethality test (BST), were evaluated in the yellow fever mosquito larvae microtiter plate (YFM) assay. The results clearly demonstrate that most acetogenins have pesticidal properties. The structure–activity relationships indicate that the compounds bearing adjacent bis-THF (tetrahydrofuran) rings with three hydroxyl groups are the most potent. Bullatacin ( 1 ) and trilobin ( 7 ) gave the best activities against YFM with LC₅₀ values of 0·10 and 0·67 mg litre^-1, respectively. Compounds showing LC₅₀ values below 1·0 mg litre^-1 in this assay are usually considered significant as new lead candidates for pesticidal development. In the BST, the corresponding LC₅₀ values were 1·6×10^-3 ( 1 ) and 9·7×10^-3 ( 7 ) mg litre^-1. This is the first report of pesticidal structure–activity relationships for a series of Annonaceous acetogenins which are known to act, at least in part, as potent inhibitors of mitochondrial NADH: ubiquinone oxidoreductase. © of SCI.     

The synthesis and larvicidal activity of N-aroyl-N′-(5-aryl-2-furoyl)ureas

A novel type of diarolyurea compound containing a furan ring has been designed and prepared. Thus, a series of N-aroyl-N′-(5-aryl-2-furoyl)ureas were synthesized by a nucleophilic addition reaction between 5-substituted furamide and aroyl isocyanate in high yield (>80%). Their structures were confirmed by IR, [¹H]NMR and elemental analyses. Bioassay showed that some of them exhibited activity against second-instar larvae of the yellow fever mosquito (Aedes aegypti L.). With the aid of artificial neural network combined with multivariable regression, a preliminary study was made of structure–activity relationship. © 1998 SCI.     

Responses of rare and common segetal species to wheat competition and fertiliser type and dose

Fertiliser application is considered crucial for determining the crop–weed competition relationship by stimulating plant growth and modulating the competition for below‐ground (soil nutrients) and above‐ground resources (e.g. light and space). Segetal species, those preferentially inhabiting cereal fields, have suffered a strong decline, owing to agricultural intensification. Under continued pressure, particularly the rarest species may disappear. In this study, we aimed to assess the competitive ability of common and rare segetal species when growing with wheat and how this competitive relationship is modulated by the type (organic and mineral) and dose (low or high) of fertilisation in a pot experiment. The segetal species grew better at higher doses of fertilisers when growing alone. However, when growing with wheat, they were outcompeted by the cereal plants. Overall, flowering was not affected by the competition with wheat under the different fertiliser regimes. Only the onset of flowering of some segetal weeds tended to be delayed by crop competition. Some rare species were more affected by the competition with wheat, indicating that they may be disadvantaged in a community context. However, not all rare segetal species tested responded in the same way, which highlights that competitiveness alone is a poor predictor of the rarity of segetal species.