Pyrrole-2 carboxamides - A novel class of insect ryanodine receptor activators

Characterization of the inheritance of field-evolved resistance to diamides in the fall armyworm (Spodoptera frugiperda) (Lepidoptera: Noctuidae) population from Puerto Rico

The fall armyworm (Spodoptera frugiperda) is one of the most destructive pests of corn. New infestations have been reported in the East Hemisphere, reaching India, China, Malaysia, and Australia, causing severe destruction to corn and other crops. In Puerto Rico, practical resistance to different mode of action compounds has been reported in cornfields. In this study, we characterized the inheritance of resistance to chlorantraniliprole and flubendiamide and identified the possible cross-resistance to cyantraniliprole and cyclaniliprole. The Puerto Rican (PR) strain showed high levels of resistance to flubendiamide (RR50 = 2,762-fold) and chlorantraniliprole (RR50 = 96-fold). The inheritance of resistance showed an autosomal inheritance for chlorantraniliprole and an X-linked inheritance for flubendiamide. The trend of the dominance of resistance demonstrated an incompletely recessive trait for H1 (♂ SUS × ♀ PR) × and an incompletely dominant trait for H2 (♀ SUS × ♂ PR) × for flubendiamide and chlorantraniliprole. The PR strain showed no significant presence of detoxification enzymes (using synergists: PBO, DEF, DEM, and VER) to chlorantraniliprole; however, for flubendiamide the SR = 2.7 (DEM), SR = 3.2 (DEF) and SR = 7.6 (VER) indicated the role of esterases, glutathione S- transferases and ABC transporters in the metabolism of flubendiamide. The PR strain showed high and low cross-resistance to cyantraniliprole (74-fold) and cyclaniliprole (11-fold), respectively. Incomplete recessiveness might lead to the survival of heterozygous individuals when the decay of diamide residue occurs in plant tissues. These results highlight the importance of adopting diverse pest management strategies, including insecticide rotating to manage FAW populations in Puerto Rico and other continents.

Divergent synthesis of pyrrole carboxamides from pyrrole carboxaldehyde and formamides/amines via oxidative amidation involving pyrrole acyl radicals

A non-traditional approach for the synthesis of pyrrole carboxamides from pyrrole carboxaldehyde and formamides or amines with catalytic amounts of nBu4NI and TBHP as oxidants is reported herein. The method is operationally simple providing straightforward access to primary, secondary, and tertiary pyrrole carboxamides in good to excellent yields utilizing inexpensive reagents under mild conditions. Unlike traditional amidations that involve ionic reactions, a mechanistic study of our current method unveils the involvement of 2- or 3-pyrrole acyl radicals that are otherwise rarely postulated. The applicability of the current method is further demonstrated in the synthesis of a drug-like compound, i.e., an optically pure carboetomidate amide.

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.

Comprehensive Overview of Diamide Derivatives Acting as Ryanodine Receptor Activators

The world's hunger is continuously rising due to conflicts, climate change, pandemics (such as the recent COVID-19), and crop pests and diseases. It is widely accepted that zero hunger is impossible without using agrochemicals to control crop pests and diseases. Diamide insecticides are one of the widely used green insecticides developed in recent years and play important roles in controlling lepidopteran pests. Currently, eight diamine insecticides have been commercialized, which target the insect ryanodine receptors. This review summarizes the development and optimization processes of diamide derivatives acting as ryanodine receptor activators. The review also discusses pest resistance to diamide derivatives and possible solutions to overcome the limitations posed by the resistance. Thus, with reference to structural biology, this study provides an impetus for designing and developing diamide insecticides with improved insecticidal activities.

Anthranilic Diamides Containing Monofluoroalkene Amide Linkers as Potential Insect RyR Activators: Design, Synthesis, Bio-evaluation, and Computational Study

In order to develop anthranilic diamides with novel chemotypes, a series of anthranilic diamides with acrylamide linkers were designed and synthesized. The results of preliminary bioassays indicated that compounds with a monofluoroalkene amide linker (Z-isomer) exhibited good larvicidal activity against lepidopteran pests. The LC₅₀ values of compound A23 against Mythimna separata and Plutella xylostella were 1.44 and 3.48 mg·L^-1, respectively, while those of chlorantraniliprole were 0.08 and 0.06 mg·L^-1, respectively. Compound A23 also exhibited the same level of lethal potency against resistant and susceptible strains of Spodoptera frugiperda at 50 mg·L^-1. Compound A23 exhibited similar symptoms as chlorantraniliprole in test larvae. Comparative molecular field analysis was conducted to demonstrate the structure-activity relationship. Central neuron calcium imaging experiments indicated that monofluoroalkene compounds were potential ryanodine receptor (RyR) activators and activated calcium channels in both the endoplasmic reticulum and the cell membrane. Molecular docking suggested that A23 had a better binding potency to P. xylostella RyR than chlorantraniliprole. The MM|GBSA dG bind value of A23 with P. xylostella RyR was 117.611 kcal·mol^-1. Monofluoroalkene was introduced into anthranilic diamide insecticides for the first time and brought a novel chemotype for insect RyR activators. The feasibility of fluoroalkenes as insecticide fragments was explored.

Marine and Anthropogenic Bromopyrroles Alter Cellular Ca2+ Dynamics of Murine Cortical Neuronal Networks by Targeting the Ryanodine Receptor and Sarco/Endoplasmic Reticulum Ca2+-ATPase

Bromopyrroles (BrPyr) are synthesized naturally by marine sponge symbionts and produced anthropogenically as byproducts of wastewater treatment. BrPyr interact with ryanodine receptors (RYRs) and sarco/endoplasmic reticulum (SR/ER) Ca²⁺-ATPase (SERCA). Influences of BrPyr on the neuronal network activity remain uncharted. BrPyr analogues with differing spectra of RYR/SERCA activities were tested using RYR-null or RYR1-expressing HEK293 and murine cortical neuronal/glial cocultures (NGCs) loaded with Fluo-4 to elucidate their mechanisms altering Ca²⁺ dynamics. The NGC electrical spike activity (ESA) was measured from NGCs plated on multielectrode arrays. Nanomolar tetrabromopyrrole (TBP, 1) potentiated caffeine-triggered Ca²⁺ release independent of extracellular [Ca²⁺] in RYR1-HEK293, whereas higher concentrations produce slow and sustained rise in cytoplasmic [Ca²⁺] independent of RYR1 expression. TBP, 2,3,5-tribromopyrrole (2), pyrrole (3), 2,3,4-tribromopyrrole (4), and ethyl 4-bromopyrrole-2-carboxylate (5) added acutely to NGC showed differential potency; rank order TBP (IC₅₀ ≈ 220 nM) > 2 ≫ 5, whereas 3 and 4 were inactive at 10 μM. TBP >2 μM elicited sustained elevation of cytoplasmic [Ca²⁺] and loss of neuronal viability. TBP did not alter network ESA. BrPyr from marine and anthropogenic sources are ecological signaling molecules and emerging anthropogenic pollutants of concern to environmental and human health that potently alter ER Ca²⁺ dynamics and warrant further investigation in vivo.

Ryanodine receptor as insecticide target

Ryanodine receptor (RyR) is one of the primary targets of commercial insecticides. The diamide insecticide family, including flubendiamide, chlorantraniliprole, cyantraniliprole, etc, targets insect RyRs and can be used to control a wide range of destructive agricultural pests. The diamide insecticides are highly selective against lepidopteran and coleopteran pests with relatively low toxicity for non-target species, such as mammals, fishes, and beneficial insects. However, recently mutations identified on insect RyRs have emerged and caused resistance in several major agricultural pests throughout different continents. This review paper summarizes the recent findings on structure and function of insect RyRs as insecticide target. Specifically, we examine the structures of RyRs from target and non-target species, which reveals the molecular basis for insecticide action and selectivity. We also examine the structural and functional changes of RyR caused by the resistance mutations. Finally, we examine the progress in RyR structure-based insecticide design, and discuss how this might help the development of new generation of green insecticides.

A Comparative Perspective on Functionally-Related, Intracellular Calcium Channels: The Insect Ryanodine and Inositol 1,4,5-Trisphosphate Receptors

Calcium (Ca²⁺) homeostasis is vital for insect development and metabolism, and the endoplasmic reticulum (ER) is a major intracellular reservoir for Ca²⁺. The inositol 1,4,5- triphosphate receptor (IP₃R) and ryanodine receptor (RyR) are large homotetrameric channels associated with the ER and serve as two major actors in ER-derived Ca²⁺ supply. Most of the knowledge on these receptors derives from mammalian systems that possess three genes for each receptor. These studies have inspired work on synonymous receptors in insects, which encode a single IP₃R and RyR. In the current review, we focus on a fundamental, common question: “why do insect cells possess two Ca²⁺ channel receptors in the ER?”. Through a comparative approach, this review covers the discovery of RyRs and IP₃Rs, examines their structures/functions, the pathways that they interact with, and their potential as target sites in pest control. Although insects RyRs and IP₃Rs share structural similarities, they are phylogenetically distinct, have their own structural organization, regulatory mechanisms, and expression patterns, which explains their functional distinction. Nevertheless, both have great potential as target sites in pest control, with RyRs currently being targeted by commercial insecticide, the diamides.