Synthesis and insecticidal efficacy of pyripyropene derivatives. Part II-Invention of afidopyropen

Insect transient receptor potential vanilloid channels as potential targets of insecticides

Chordotonal organs are miniature sensory organs present in insects. Chordotonal organs depend on transient receptor potential (TRP) channels. Transient receptor potential vanilloid (TRPV) channels are the only TRPs identified that can act as targets of insecticides. By binding with TRPV channels, insecticides targeting the chordotonal organs trigger the inflow of calcium ions, resulting in abnormal function of the chordotonal organ to achieve the goal of eliminating pests. TRPV channels are highly expressed in various developmental stages and tissue parts of insects and play an important role in the whole life history of insects. In this review, we will discuss the structure and types of TRPV channels as well as their genetic relationships in different species. We also systematically reviewed the recent progress of TRPV channels as insecticide targets, demonstrating that TRPV channels can be used as the target of new high-efficiency insecticides.

Afidopyropen suppresses silkworm growth and vitality by affecting carbohydrate metabolism and immune function

Afidopyropen has strong insecticidal toxicity to sucking pests by silencing the vanilloid-type transient receptor potential (TRPV) channels. However, the toxicity of afidopyropen to the Lepidoptera model insect silkworm remain unknown. In this study, the LC50 of afidopyropen to the silkworm at 72 h exposure was 256.82 mg/L. This indicates that afidopyropen is moderately toxic to the silkworm. Long-term exposure to concentrations of 100 mg/L, or less, of afidopyropen, significantly reduced silkworm growth, vitality, silk protein synthesis, and fecundity. A total of 220 differentially expressed genes (DEGs) were detected by transcriptome sequencing, among which 166 were downregulated and 54 were upregulated. Gene Ontology (GO) enrichment analysis showed that the DEGs were enriched in the immune system, immune response and carbohydrate metabolism. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis indicated that DEGs were primarily concentrated in carbohydrate metabolism and biosynthesis of neomycin, kanamycin and gentamicin. Genes related to carbohydrate metabolism and immune system pathways in silkworm were detected by quantitative real-time PCR. The results showed that the genes related to carbohydrate metabolism, silk protein synthesis, and immune response were significantly downregulated. These genes included BCL-6 corepressor-like protein 1 (BCORL1), hexokinase type 2 (HEXO2), phosphoserine aminotransferase 1 (PSAT1), relish (Rel), peptidoglycan recognition protein 2 (PGRP2) and 27 kda glycoprotein precursor (P27K). The data demonstrated the toxic effects of afidopyropen against the silkworm and its regulation of genes responsible for immune function and abscissa carbohydrate metabolism.

Insecticide discovery-"Chance favors the prepared mind"

New options for pest insect control, including new insecticides, are needed to ensure a plentiful food supply for an expanding global population. Any new insecticides must meet the increasingly stringent regulatory requirements for mammalian and environmental safety, and also address the need for new chemistries and modes of action to deal with resistance to available insecticides. As underscored by a paraphrase of a quote from Louis Pasteur "Chance favors the prepared mind", the agrochemical industry uses a variety of approaches that attempt to improve on "chance" for the discovery of new insecticides. Although there are a number of approaches to the discovery of new insecticidal active ingredients (AIs), historically most insecticides are based on a pre-existing molecule or product either from a competitor or from an internal company source. As such the first examples of a new insecticide representing a new type or class of AI (First-in-Class: FIC) are important as prototypes for other AIs stimulating further spectrum, efficacy, physicochemical, and environmental safety refinements. FIC insecticides also represent a measure of innovation. Understanding the origins of these FIC compounds and the approaches used in their discovery can provide insights into successful strategies for future new classes of insecticides. This perspective will focus on an analysis of the approaches that have been used for discovery of FIC insecticides highlighting those approaches that have been the most successful and providing a reference point for current and future directions.

Natural Product-Based Crop Protection Compounds─Origins and Future Prospects

The continuing need to protect food and fiber production to address the demands of an expanding global population requires new pest management tools for crop protection. Natural products (NPs) have been and continue to be a key source of inspiration for new active ingredients (AIs) for crop protection, accounting for 17% of all crop protection AIs. However, potentially 50% of all crop protection compounds have or could have a NP origin if NP synthetic equivalents (NPSEs, synthetic compounds discovered by other approaches but for which a NP model also happens to exist) are also considered. The real and hypothetical NPs have their greatest impact as insight for new classes of crop protection compounds. Among the different product areas, NPs have their largest influence on the discovery of new insecticides, while herbicides have been the least affected by mining NPs for new AIs. While plants have historically been the largest (60% of the total) source of NPs of AIs for crop protection, in the last 30 years, bacterial NPs have become the largest source (42% of the total) of new classes (first in class) of NP-inspired crop protection AIs. Interest in NPs for crop protection continues, an aspect that is highlighted by the notable rise in the numbers of publications and patents on this topic, especially in the last 20 years. The present analysis further illustrates the continuing interest and value in NPs as sources of and inspiration for new classes of crop protection compounds.

Innovation in insecticide discovery: Approaches to the discovery of new classes of insecticides

The continuing demand for agrochemical insecticides that can meet increasing grower, environmental, consumer and regulatory requirements creates the need for the development of new solutions for managing crop pest insects. The development of resistance to the currently available insecticidal products adds another critical driver for new insecticidal active ingredients (AIs). One avenue to meeting these challenges is the creation of new classes of insecticidal molecules to act as starting points and prototypes stimulating further spectrum, efficacy and environmental impact refinements. A new class of insecticides is foreshadowed by the first molecule exemplifying that class (first-in-class, FIC) and offers one measure of innovation within the agrochemical industry. Most insecticides owe their discovery to competitor-inspired (i.e. competitor patents/products) or next-generation (follow-on to a company's pre-existing product) strategies. In contrast, FIC insecticides primarily emerge from a bioactive hypothesis approach, with the largest segment resulting from the exploration of new areas of chemistry/heterocycles and underexploited motifs. Natural products also play an important role in the discovery of FIC insecticides. Understanding the origins of these FIC compounds and the approaches used in their discovery can provide insights into successful strategies for future FIC insecticides. This review analyses information on historic and recently introduced FIC insecticides. Its main objective has been to identify the most successful discovery strategies for identifying new agrochemical solutions to meet the challenge of minimizing crop losses resulting from insects. © 2022 Society of Chemical Industry.

Characterization of Field-Evolved Resistance to Afidopyropen, a Novel Insecticidal Toxin Developed from Microbial Secondary Metabolites, in Bemisia tabaci

Afidopyropen, a newly identified chemical, is a derivative of pyripyropene A, which is produced by the filamentous fungus Penicillium coprobium. It is a promising novel pesticide applied against whiteflies in agriculture. In this study, the reversion and selection, cross-resistance patterns, synergistic effects, and fitness costs of afidopyropen resistance were studied in a field-developed resistant population of B. tabaci. Compared to a reference MED-S strain, the field-developed resistant Haidian (HD) population showed 36.5-fold resistance to afidopyropen. Significant reversion of resistance to afidopyropen was found in the HD population when it was kept with no selective pressure of the insecticide. The HD-Afi strain, developed from the HD population with afidopyropen pressure, developed 104.3-fold resistance to afidopyropen and significant cross-resistance to sulfoxaflor. Piperonyl butoxide (PBO) largely inhibited afidopyropen resistance in the HD-Afi strain, which indicates that P450 monooxygenase could be involved in the resistance. Significant fitness costs associated with afidopyropen resistance were observed in HD-Afi. This study indicates that a rotation of afidopyropen with other chemical control agents could be useful for impeding afidopyropen resistance in B. tabaci. In addition, we expanded upon the understanding of resistance to afidopyropen, offering evidence suggesting the importance of devising better strategies for the management of whiteflies.

Afidopyropen, a novel insecticide originating from microbial secondary extracts

Afidopyropen, a novel insecticide, is a derivative of pyripyropene A, which is produced by the filamentous fungus Penicillium coprobium. Afidopyropen has strong insecticidal activity against aphids and is currently used as a control agent of sucking pests worldwide. In this study, we summarized the biological properties and field efficacies of its derivatives against agricultural pests using official field trials conducted in Japan. Afidopyropen showed good residual efficacies against a variety of aphids, whiteflies and other sucking pests under field conditions. Furthermore, toxicological studies revealed its safety profiles against nontarget organisms, such as the honeybee, natural enemies and other beneficial insects, as well as mammals. Thus, afidopyropen is a next-generation agrochemical for crop protection that has a low environmental impact.

Talaromyces-Insect Relationships

Facing the urgent need to reduce the input of agrochemicals, in recent years, the ecological relationships between plants and their associated microorganisms have been increasingly considered as an essential tool for improving crop production. New findings and data have been accumulated showing that the application of fungi can go beyond the specific role that has been traditionally assigned to the species, employed in integrated pest management as entomopathogens or mycoparasites, and that strains combining both aptitudes can be identified and possibly used as multipurpose biocontrol agents. Mainly considered for their antagonistic relationships with plant pathogenic fungi, species in the genus Talaromyces have been more and more widely reported as insect associates in investigations carried out in various agricultural and non-agricultural contexts. Out of a total of over 170 species currently accepted in this genus, so far, 27 have been found to have an association with insects from 9 orders, with an evident increasing trend. The nature of their mutualistic and antagonistic relationships with insects, and their ability to synthesize bioactive compounds possibly involved in the expression of the latter kind of interactions, are analyzed in this paper with reference to the ecological impact and applicative perspectives in crop protection.

Structure Simplification of Natural Products as a Lead Generation Approach in Agrochemical Discovery

Natural products (NPs) have a long history as sources of compounds for crop protection. Perhaps a more important role for NPs has been as models and inspiration for the discovery and development of synthetic crop protection compounds. NPs and their synthetic mimics account for 18% of all crop protection compounds, whereas another 38% of all crop protection compounds have a NP that could have served as a model. Because NPs are often complex molecules, have limited availability, or possess structural features that constrain their suitability for use in agricultural settings, a key element in NP-inspired compounds is the simplification of the NP structure to provide a synthetically accessible molecule that possesses the physicochemical properties needed for use in crop protection. Herein we review a series of examples of NP mimics that demonstrate the structural or synthetic simplification of NPs as a guide for the discovery of future NP-inspired agrochemicals focused on fungicides, herbicides, and insecticides.

Microbial Toxins in Insect and Nematode Pest Biocontrol

Invertebrate pests, such as insects and nematodes, not only cause or transmit human and livestock diseases but also impose serious crop losses by direct injury as well as vectoring pathogenic microbes. The damage is global but greater in developing countries, where human health and food security are more at risk. Although synthetic pesticides have been in use, biological control measures offer advantages via their biodegradability, environmental safety and precise targeting. This is amply demonstrated by the successful and widespread use of Bacillusthuringiensis to control mosquitos and many plant pests, the latter by the transgenic expression of insecticidal proteins from B. thuringiensis in crop plants. Here, I discuss the prospects of using bacterial and fungal toxins for pest control, including the molecular basis of their biocidal activity.

Status and outlook for acaricide and insecticide discovery

To guarantee sustainability and progress, the agrochemical industry is faced with several major challenges. Currently, loss of active ingredients due to consumer perception, changing grower needs and ever-changing regulatory requirements is far higher than the number being introduced into the market. Therefore, there is a need to develop new products that can provide improved efficacy, selectivity and favorable environmental profiles. Strategies to achieve these goals are the search for acaricides and insecticides with new modes of action, or the discovery of novel molecules with activity on the most attractive target sites having resistance breaking properties against pest species. In this context, the introduction of halogen atoms or asymmetric centers into an active ingredient remains an important tool to modulate their properties, but so too is the pro-pesticide concept. This review gives an overview of agrochemicals launched over the past 8 years, reflects new insights into known mechanisms of action, and describes the status and outlook for acaricide and insecticide discovery.

Chemistry of fungal meroterpenoid cyclases

Covering: up to July 2020Fungal meroterpenoid cyclases are a recently discovered emerging family of membrane-integrated, non-canonical terpene cyclases. They catalyze the conversion of hybrid isoprenic precursors towards complex scaffolds and are therefore of great importance in the structure diversification in meroterpenoid biosynthesis. The products of these pathways exhibit intriguing molecular scaffolds and highly potent bioactivities, making them privileged structures from Nature and attractive candidates for drug development or industrial applications. This review will provide a comprehensive and comparative view on fungal meroterpenoid cyclases, their intriguing chemistries and importance for the scaffold formation step towards polycyclic meroterpenoid natural products.