Application of Natural Bioresources to Sustainable Agriculture: A C-Glycoside Insecticide Based on N-Acetyl-glucosamine for Regulating Insect Molting of Ostrinia furnacalis

Design of Inhibitors Targeting Chitin-Degrading Enzymes by Bioisostere Substitutions and Scaffold Hopping for Selective Control of Ostrinia furnacalis

Chitin-degrading enzymes are critical components in regulating the molting process of the Asian corn borer and serve as potential targets for controlling this destructive pest of maize. Here, we used a scaffold-hopping strategy to design a series of efficient naphthylimide insecticides. Among them, compound 8c exhibited potent inhibition of chitinase from OfChi-h and OfChtI at low nanomolar concentrations (IC50 = 1.51 and 9.21 nM, respectively). Molecular docking simulations suggested that 8c binds to chitinase by mimicking the interaction of chitin oligosaccharide substrates with chitinase. At low ppm concentrations, compound 8c performed comparably to commercial insecticides in controlling the highly destructive plant pest, the Asian corn borer. Tests on a wide range of nontarget organisms indicate that compound 8c has very low toxicity. In addition, the effect of inhibitor treatment on the expression of genes associated with the Asian corn borer chitin-degrading enzymes was further investigated by quantitative real-time polymerase chain reaction. In conclusion, our study highlights the potential of 8c as a novel chitinase-targeting insecticide for effective control of the Asian corn borer, providing a promising solution in the quest for sustainable pest management.

A Potential Multitarget Insect Growth Regulator Candidate: Design, Synthesis, and Biological Activity of Novel Acetamido Derivatives Containing Hexacyclic Pyrazole Carboxamides

Insect growth regulators (IGRs) are important green insecticides that disrupt normal growth and development in insects to reduce the harm caused by pests to crops. The ecdysone receptor (EcR) and three chitinases OfChtI, OfChtII, and OfChi-h are closely associated with the molting stage of insects. Thus, they are considered promising targets for the development of novel insecticides such as IGRs. Our previous work identified a dual-target compound 6j, which could act simultaneously on both EcR and OfChtI. In the present study, 6j was first found to have inhibitory activities against OfChtII and OfChi-h, too. Subsequently, taking 6j as a lead compound, 19 novel acetamido derivatives were rationally designed and synthesized by introducing an acetamido moiety into the amide bridge based on the flexibility of the binding cavities of 6j with EcR and three chitinases. Then, their insecticidal activities against Plutella xylostella (P. xylostella), Ostrinia furnacalis (O. furnacalis), and Spodoptera frugiperda (S. frugiperda) were carried out. The bioassay results revealed that most of these acetamido derivatives possessed moderate to good larvicidal activities against three lepidopteran pests. Especially, compound I-17 displayed excellent insecticidal activities against P. xylostella (LC50, 93.32 mg/L), O. furnacalis (LC50, 114.79 mg/L), and S. frugiperda (86.1% mortality at 500 mg/L), significantly better than that of 6j. In addition, further protein validation and molecular docking demonstrated that I-17 could act simultaneously on EcR (17.7% binding activity at 8 mg/L), OfChtI (69.2% inhibitory rate at 50 μM), OfChtII (71.5% inhibitory rate at 50 μM), and OfChi-h (73.9% inhibitory rate at 50 μM), indicating that I-17 is a potential lead candidate for novel multitarget IGRs. This work provides a promising starting point for the development of novel types of IGRs as pest management agents.

Identifying Chlorella vulgaris and Chlorella sorokiniana as sustainable organisms to bioconvert glucosamine into valuable biomass

Chitin is a major component of various wastes such as crustacean shells, filamentous fungi, and insects. Recently, food-safe biological and chemical processes converting chitin to glucosamine have been developed. Here, we studied microalgae that can uptake glucosamine as vital carbon and nitrogen sources for valuable alternative protein biomass. Utilizing data mining and bioinformatics analysis, we identified 29 species that contain the required enzymes for glucosamine to glucose conversion. The growth performance of the selected strains was examined, and glucosamine was used in different forms and concentrations. Glucose at a concentration of 2.5 g/L was required to initiate glucosamine metabolic degradation by Chlorella vulgaris and Chlorella sorokiniana. Glucosamine HCl and glucosamine phosphate showed maximum cell counts of about 8.5 and 9.0 log/mL for C. sorokiniana and C. vulgaris in 14 days, respectively. Enzymatic hydrolysis of glucosamine increased growth performance with C. sorokiniana by about 3 folds. The adapted strains were fast-growing and could double their dry biomasses during the same incubation time. In addition, adapted C. sorokiniana was able to tolerate three times glucosamine concentration in the medium. The study illustrated possible strategies for employing C. sorokiniana and C. vulgaris to convert glucosamine into valuable biomass in a more sustainable way.

Recent advances in glycoside hydrolase family 20 and 84 inhibitors: Structures, inhibitory mechanisms and biological activities

Glycoside hydrolase family 20 (GH20) β-N-acetyl-d-hexosaminidase (Hex) catalyzes the cleavage of glycosidic linkages in glycans, glycolipids and glycoproteins, and is involved in glycoprotein modification, metabolism of glycoconjugate and the degradation of chitin in fungal cell walls and arthropod exoskeletons. GH84 O-β-N-acetyl-d-glucosaminidase (OGA), which is mechanistically similar related to GH20, participates in the O-GlcNAcylation modification, hydrolyzing the O-GlcNAc moiety from protein acceptors. Hex and OGA are of interest due to their potential for the treatment of disorder diseases and plant protection. Hex inhibitors act as molecular chaperones to treat lysosomal storage disease and as growth regulators to arrest insect molting. Inhibition of OGA is a promising therapeutic approach to treat tau pathology in neurodegenerative diseases such as Alzheimer's disease. However, since Hex and OGA exhibit similar active sites, there are challenges in designing highly selective inhibitors. The elucidation of the structural basis of the catalytic mechanism and substrate binding mode of Hex and OGA has provided core information for virtual screening and rational design of inhibitors. A large number of high-potency and selective inhibitors have been developed in the last five years. In this review, we focus on the recent advances in the structural modification, inhibitory activity, binding mechanisms and biological evaluation of Hex and OGA inhibitors, which will facilitate the development of new drugs and agrochemicals.