Flometoquin (FLO) is a novel quinoline-type insecticide that elicits a quick knock-down effect against target pests; however, its mode of action (MoA) remains unknown. In this study, we investigated its MoA systematically, using varying biochemical techniques. Since FLO-treated insects exhibited symptoms similar to those induced by respiratory inhibitors, we examined the effect of FLO on respiratory enzyme complexes using mitochondria isolated from different insects (housefly, diamondback moth, and western flower thrips). We found that FLO itself is not active; however, its deacylated metabolite, FloMet, specifically inhibits the activity of ubiquinol-cytochrome c oxidoreductase (complex III) in mitochondria at the nM level. Ligand binding assays and monitoring the reduction kinetics of cytochrome hemes b and c₁ clearly revealed that FloMet inhibits complex III by binding to the Q_i site.

In recent years, the stable supply of natural rubber has been threatened by a new leaf fall disease (LFD) caused by filamentous fungi. We screened pesticides to control the growth of Neopestalotiopsis sp. and Colletotrichum sp., which are considered to be the causal agents of LFD in rubber trees. We identified two effective pesticides, Quinondo 80% WP and Topsin M WP. When these two candidate pesticides were used in combination at 10 ppm each, there was enhanced inhibition of growth of both fungal species. Furthermore, the use of Quinondo 80% WP was shown to suppress the development of necrotic lesions caused by Neopestalotiopsis in rubber seedlings. These results suggest that Quinondo 80% WP is effective in controlling the spread of damage caused by LFD infection in rubber trees, and further verification of the concentration and method of application is needed to further demonstrate its effectiveness.

The insecticide susceptibility of Helopeltis theivora Waterhouse (Hemiptera: Miridae) is being evaluated using shoot and glass-vial assay as described by IRAC. However, the reliability of the assay depends on feeding preference and contact toxicity. Hence, the cocoa pod was used as a substrate to test the susceptibility of H. theivora in comparison with existing methods. The experimental results revealed that the LC₅₀ value of all of the insecticides was relatively lower in the pod bioassay than the other two methods and exhibited maximum mortality within 6 hr of post-exposure. Among insecticides, fipronil was the most effective molecule followed by lambda-cyhalothrin. H. theivora, which prefers to feed on a pod due to more tissue turgidity, thus facilitated adequate sap ingestion; whereas, these were limited in shoot and glass-vial bioassays. Therefore, it could be used as a methodology to determine the susceptibility of H. theivora against a wide range of insecticide molecules.

The Cry1Fa insecticidal protein from Bacillus thuringiensis (Bt) was expressed on the surface of Bacillus subtilis (Bs) spores to create transgenic Bs spores referred to as Spore-Cry1Fa. Cry1Fa, along with its leader sequence, was connected to the carboxyl end of a Bs spore outercoat protein, CotC, through a flexible linker. The Arg-27 residue of the Cry1Fa protein was mutated to Leu to prevent detachment from the spores due to protease digestion. The expression of the Cry protein on the Bs spores was confirmed by fluorescence microscopy using an anti-Cry1Fa antibody. The Cry protein, tightly anchored to the spore surface, appeared to be functional in terms of receptor binding. Spore-Cry1Fa bound to Sf9 cells expressing Spodoptera frugiperda (Sf) ABCC2 transporter and killed the cells within 60 min. Additionally, nano-lipid particles of SfABCC2 were produced using styrene-maleic acid (SMA) to demonstrate the binding to Spore-Cry1Fa.

Our group previously identified MS-347a (1) as a new fungicide candidate from the culture broth of the mutant strain, Aspergillus sp. KTF-0058, which had the laeA gene inserted. This mutant strain was able to produce a sufficient supply of 1, allowing for its use to investigate the structure–activity relationship. To this end, we synthesized 11 derivatives and evaluated their antifungal activity. Among these derivatives, the aldehyde derivative exhibited superior antifungal potency as compared to 1, and some acyl derivatives were able to maintain the antifungal activity of 1 despite significant structural changes. From these results, it is found that the aldehyde derivative is one of the most promising fungicidal candidates, and the introduction of acyl groups could be utilized to create chemical probes for target-identification experiments.

Agonists of insect hormones, namely molting hormone (MH) and juvenile hormone (JH), disrupt the normal growth of insects and can be employed as insecticides that are harmless to vertebrates. In this study, a series of experiments and computational analyses were conducted to rationally design novel insect hormone agonists. Syntheses and quantitative structure–activity relationship (QSAR) analyses of two MH agonist chemotypes, imidazothiadiazoles and tetrahydroquinolines, revealed that the structural factors important for the ligand–receptor interactions are significantly different between these chemotypes. On the other hand, a virtual screening cascade combining ligand- and structure-based methods identified a piperazine derivative as a novel JH agonist. The results obtained in this study will be useful for the future development of novel insect growth regulators.

The syntheses of stereoisomers of butane, butanediol, γ-butyrolactone, tri-substituted tetrahydrofuran (7,9′-epoxy), furofuran, tetra-substituted tetrahydrofuran (7,7′-epoxy and 7,8′-epoxy-8,7′-neolignan), benzylidene, coumarin, indan, and pyran type lignans were achieved. All the stereoisomers of the butane type lignans showed larvicidal activity and anti-phytopathogenic fungal activity. The γ-butyrolactone lignan showed stereospecific cytotoxicity against insect cells. Stereo/enantiospecific plant growth inhibitory activity was observed in tri-substituted tetrahydrofuran, tetra-substituted tetrahydrofuran (7,7′-epoxy), coumarin, and pyran type lignans. The furofuran lignan both inhibited and promoted growth in plants. Stereo/enantiospecific anti-phytopathogenic fungal activity was observed in tetra-substituted tetrahydrofuran (7,7′-epoxy) and E-benzylidene lignans.

We investigated whether various modified cyclodextrins (CDs) and emulsifiers could be applied as dispersing agents in ready biodegradability tests of poorly water-soluble substances. Trimethylated α-, β-, and γ-CDs and partially methylated β-CD were not biodegraded in the test period but accelerated the biodegradation of octabenzone and anthraquinone. The process by which trimethylated α-, β-, and γ-CDs enhance the biodegradation of test substances has been partially uncovered. These CDs create inclusion complexes with the substances, which then coalesce into larger aggregates. These aggregates disperse throughout the testing medium and attach to clusters of activated sludge, known as flocs. This close contact with the sludge speeds up the breakdown of the hydrophobic substances being tested.

When a test substance is poorly water-soluble, it can be adsorbed onto silica gel to facilitate dispersibility in a ready biodegradability test. To uniformly adsorb the test substance onto silica gel, the substance is dissolved in a solvent and then mixed with the silica gel. It is desirable for the solvent to completely evaporate afterward. In this study, we identified n-hexane as a suitable solvent for this purpose. Furthermore, through fluorescence observation, we revealed that the test substance adsorbed onto the silica gel adhered to activated sludge flocs. This is thought to improve contact between the test substance and microorganisms, thereby accelerating biodegradation.

The chemical synthesis of biologically active natural products has diverse objectives and missions, including 1) determining the structures of the natural products, 2) providing synthetic samples for studying the activity and function, 3) providing a basis for applied research on these compounds, etc. I have studied various biologically active natural products and conducted synthetic studies on these compounds with various objectives. In this review, I present the results of my research, focusing on natural products with potential as agrochemicals.