Lactones: Part 11. Feeding-deterrent activity of some bi- and tricyclic terpenoid lactones

The feeding-deterrent activities of thirteen synthetic terpenoid lactones, including isomeric bicyclic gamma-spirolactones with the limonene system and tricyclic gamma-lactones with the pinane system, were determined towards three storage pest insects: the adults of Sitophilus granarius, the adults and larvae of Tribolium confusum and the larvae of Trogoderma granarium. The configuration of chiral centres, as well as the presence of additional functional groups (double bond, iodine and hydroxy group) are important for antifeeding activity.     

Inhibitory action of Cerrado plants against mammalian and insect α-amylases

A total of 185 hexanic, dichloromethanic, ethanolic and hydroethanolic extracts from 24 species of Cerrado plants, were tested against Zabrotes subfasciatus, Acanthoscelides obtectus, and human saliva α-amylases. Twelve crude extracts presented inhibition rates greater than 80% against digestive α-amylases of the insect pest Z. subfasciatus, at a concentration of 1 mg mL⁻¹. These extracts were also tested against A. obtectus and human saliva α-amylases to verify their affinity and specificity of action. The hydroethanolic Kielmeyera coriacea stem bark extract presented a strong inhibitory potential, with IC₅₀ values of 110 μg mL⁻¹ for Z. subfasciatus and 272.12 μg mL⁻¹ for A. obtectus, in addition to a 97.09% reduction in enzyme activity of human saliva α-amylases at 125 μg mL⁻¹. The hexanic Aspidosperma macrocarpon root wood extract totally inhibited the activity of Z. subfasciatus α-amylases, reduced the enzyme activity of A. obtectus by 14.69% at 1 mg mL⁻¹, but did not alter the activity of human saliva α-amylases, thus characterizing greater inhibition affinity and specificity. The results suggest that the application of plant extracts against insect α-amylases represent a promising biotechnological tool for development of new insect pest control strategies, with noticeable affinity and specificity of action against different target enzymes.     

Synthesis and structure–activity relationship analysis of bicyclophosphorothionate blockers with selectivity for housefly γ‐aminobutyric acid receptor channels

BACKGROUND: Bicyclophosphorothionates (2,6,7‐trioxa‐1‐phosphabicyclo[2.2.2]octane‐1‐sulfides) are blockers (or non‐competitive antagonists) of γ‐aminobutyric acid (GABA) receptor channels. Twenty‐two bicyclophosphorothionates with different 3‐ and 4‐substituents were synthesised, and [³H]4′‐ethynyl‐4‐n‐propylbicycloorthobenzoate (EBOB) binding assays were performed to evaluate their affinities for housefly and rat GABA receptors. RESULTS: Introduction of an isopropyl group at the 3‐position enhanced the affinity of bicyclophosphorothionates for housefly GABA receptors and reduced the affinity towards rat GABA receptors. The 4‐isopentyl‐3‐isopropylbicyclophosphorothionate showed the highest affinity for housefly GABA receptors (IC₅₀ = 103 nM ) among the analogues tested, while the 4‐cyclohexylbicyclophosphorothionate showed the highest affinity for rat GABA receptors (IC₅₀ = 125 nM ). Among the bicyclophosphorothionates synthesised to date, the former analogue exhibited the highest selectivity for housefly GABA receptors, with an IC₅₀^rat/IC₅₀^fly ratio of approximately 97. Three‐dimensional GABA receptor models successfully explained the structure–activity relationships of the bicyclophosphorothionates. CONCLUSION: The results indicate that minor structural modifications of blockers can change their selectivity for insect versus mammalian GABA receptors. The substituent at the 3‐position of the bicyclophosphorothionates dictates selectivity for housefly versus rat GABA receptors. This information should prove useful for the design of safer insecticides and parasiticides. Copyright © 2010 Society of Chemical Industry     

Callose and β‐1,3‐glucanase inhibit Phytophthora cinnamomi in a resistant avocado rootstock

Phytophthora root rot (PRR) of avocado, caused by Phytophthora cinnamomi, is a significant threat to sustainable production wherever the crop is grown. Resistant rootstocks in combination with phosphite applications are the most effective options for managing this disease. Recently, the mechanisms underpinning PRR resistance have been investigated by the avocado community. Here, biochemical assays and confocal and scanning electron microscopy were used to investigate early defence responses in PRR resistant and ‐susceptible avocado rootstocks. Zoospore germination and subsequent hyphal growth for the pathogen were significantly inhibited on the surface of resistant avocado roots. When penetration occurred in the resistant R0.06 rootstock, callose was deposited in the epidermal cells, parenchyma and cortex of roots. In addition, β‐1,3‐glucanase was released early (6 h post‐inoculation, hpi) in response to the pathogen, followed by a significant increase in catalase by 24 hpi. In contrast, susceptible R0.12 roots responded only with the deposition of lignin and phenolic compounds incapable of impeding pathogen colonization. In this study, PRR resistance was attributed to a timely multilayered response to infection by P. cinnamomi.     

Enantioselective catalysis for agrochemicals: synthetic routes to (S)-metolachlor, (R)-metalaxyl and (αS,3R)-clozylacon

The application of enantioselective catalytic methods for the technical preparation of chiral agrochemicals is illustrated for three active ingredients of the acylanilide type. The key step for the technical synthesis of the herbicide (S)-metolachlor is the enantioselective hydrogenation of an imine intermediate using a novel iridium ferrocenyldiphosphine catalyst with an unprecedented high activity and 80% ee. (R)-metalaxyl and (αS,3R)-clozylacon were synthesized via the enantioselective hydrogenation of corre-sponding enamide precursors with Rh and Ru/binap catalysts with >95% and 99% enantiomeric purity, respectively. © 1998 Society of Chemical Industry     

Long‐lasting β‐aminobutyric acid‐induced resistance protects tomato fruit against Botrytis cinerea

Minimizing losses to pests and diseases is essential for producing sufficient food to feed the world's rapidly growing population. The necrotrophic fungus Botrytis cinerea triggers devastating pre‐ and post‐harvest yield losses in tomato (Solanum lycopersicum). Current control methods are based on the pre‐harvest use of fungicides, which are limited by strict legislation. This investigation tested whether induction of resistance by β‐aminobutyric acid (BABA) at different developmental stages provides an alternative strategy to protect post‐harvest tomato fruit against B. cinerea. Soil‐drenching plants with BABA once fruit had already formed had no impact on tomato susceptibility to B. cinerea. However, BABA application to seedlings significantly reduced post‐harvest infection of fruit. This resistance response was not associated with a yield reduction; however, there was a delay in fruit ripening. Untargeted metabolomics revealed differences between fruit from water‐ and BABA‐treated plants, demonstrating that BABA triggered a defence‐associated metabolomics profile that was long lasting. Targeted analysis of defence hormones suggested a role of abscisic acid (ABA) in the resistance phenotype. Post‐harvest application of ABA to the fruit of water‐treated plants induced susceptibility to B. cinerea. This phenotype was absent from the ABA‐exposed fruit of BABA‐treated plants, suggesting a complex role of ABA in BABA‐induced resistance. A final targeted metabolomic analysis detected trace residues of BABA accumulated in the red fruit. Overall, it was demonstrated that BABA induces post‐harvest resistance in tomato fruit against B. cinerea with no penalties in yield.     

Recovery of solubilized δ‐endotoxin from Bacillus thuringiensis subsp kurstaki fermentation broth

Insecticidal δ‐endotoxin proteins, degraded from parasporal crystals by protease, were recovered by a simple procedure using heat treatment, solubilization, and ultrafiltration of a fermentation broth of Bacillus thuringiensis subsp kurstaki HD‐1. A 68 kDa insecticidal protein was obtained and characterized by SDS‐PAGE. The procedure described gave a nearly quantitative recovery of toxicity. Furthermore, bioassay results on larvae of the diamondback moth (Plutella xylostella) showed that the 68 kDa δ‐endotoxin fraction (P1) was the principal insecticidal component to this target insect. A similar molecular mass polypeptide P2 (65 kDa) which was solubilized together with P1 from the parasporal crystals, gave relatively low mortality. © 2000 Society of Chemical Industry