Rynaxypyr

Rynaxypyr A New Anthranilic Diamide Insecticide Acting at the Ryanodine Receptor... 

Figure 1. Rynaxypyr 3-bromo-N-[4-chloro-2-methyl-6-[(methylamino)carbonyl -phenyl -l-(3-chloro-2-pyridinyl)-l H-pyrazole-5-carboxamide. A new anthranilic diamide insecticide acting at the insect ryanodine receptor.

Figure 8. Comparative activity of Rynaxypyr against cells expressing insect and mammalian RyRs.

Rynaxypyr fails to activate RyRs when tested at concentrations up to 100 pM. This large differential selectivity toward insect RyRs is highly consistent with the observed low mammalian toxicity and almost certainly a contributing factor to the low mammalian toxicity. 

In summary, a novel class of chemistry has been discovered with exceptional insecticidal activity against a broad spectrum of lepidoptera. These compounds have been found to exhibit their action through release of intracellular Ca stores mediated by the ryanodine receptor. The first commercial member of this class, Rynaxypyr, demonstrates outstanding lab and field activity on all major species of lepidoptera with lab rates in the range of 0.01-0.06 ppm. This level of activity is significantly better than current commercial standards and shows remarkable consistency across a broad insect spectrum. Rynaxypyr thus offers exceptional promise as a new product for crop protection based on this combination of a new mode of action with outstanding insecticidal properties. 

Elucidation of the Mode of Action of Rynaxypyr , a Selective Ryanodine Receptor Activator... 

Lepidopteran larvae exposed to anthranilic diamides exhibit rapid feeding cessation, general lethargy, constrictive muscle paralysis, and regurgitation. One of the earliest symptoms observed was reduction in heart rate. Manduca sexta larvae showed greater than a 50% decrease in heart beat frequency ten minutes following injection with Rynaxypyr (30 ng). Among anthranilic diamides evaluated, similar rank potency was found for this cardio-inhibitory effect and lepidopteran toxicity. 

Rynaxypyr Stimulates Release of RyR-Mediated Internal Ca Stores... 

Rynaxypyr releases internal Ca stores with an EC50 value of 36 nM (b) Inset Typical Ca response for Rynaxypyr . 

A radiolabeled anthranilic diamide, H-D18, was prepared and found to exhibit specific, saturable binding to muscle membranes. Interestingly, under conditions of high CaCl2 (500 pM), ryanodine enhances H-D18 binding up to 8-fold, with a = 44 nM and B, = 9690 fmol/mg [6]. In this preparation, Rynaxypyr potently displaces H-D18 with an IC5Q value of 4 nM. As was observed with lepidopteran toxicity, a linear relationship was revealed between Ca mobilization and the ability of anthranilic diamides to displace H-D18. 

Western blot analysis of P. americana membranes and photo-affinity studies using a tritiated azido-anthranilic diamide revealed that Rynaxypyr and related analogs bind directly to the ryanodine receptor rather than to an accessory protein. 

H. virescens RyR. Sf9 cells expressing recombinant D. mdanogaster and H. virescens RyRs exhibit comparable Rynaxypyr sensitivity to that observed with native P. americana neurons. Expression of such recombinant insect RyRs offers utility for target screening and is the basis of a patent application [8]. 

Figure 3. Wild type Sf9 cells (gray trace) possess internal Ca stores sensitive to the SERCA pump inhibitor, cyclopiazonic acid (CPA), but lack functional RyRs. Stable expression of the full-length H. virescens RyR clone (black trace) confers sensitivity to both caffeine and Rynaxypyr ...

Mammals possess three isoforms of the ryanodine receptor RyRl and RyR2, distributed primarily in skeletal and cardiac muscle, respectively, and RyR3 distributed more heterogeneously. Insects, however, express a single form of the receptor, sharing only 47% sequence homology [9]. Comparative studies were conducted to determine Rynaxypyr s ability to activate mammalian RyRs. 

Though ryanodine and caffeine show similar potency against insect and mammalian receptors (not shown), differential selectivity is observed for Rynaxypyr . 

Rynaxypyr is a highly potent and selective activator of insect RyRs. Activation of these receptors causes unregulated release of internal stores leading to store... 

The discovery of a novel class of anthranilic diamide insecticides having exceptional activity against a broad spectrum of Lepidoptera at extremely low rates of application has successfully led to the commercialization of Rynaxypyr (2). Compounds of this chemistry class exert their effect by causing release of intracellular Ca stores in muscle cells by activation of the ryanodine receptor. As a new mode-of-action product with outstanding insecticidal properties, Rynaxypyr offers great promise for the marketplace. 

Anthranilic Diamide, Anfhranilamide, Rynaxypyr, Phenylpyrazole, Pyridylpyrazole, Phenylpyrimidine, Pyridylpyrimidine, Insecticide, Ryanodine Receptor... 

T. Masaki et al., Nihon Nohyaku and Bayer CropScience, Japan and Germany, and Elucidation of the mode of action of Rynaxypyr, a selective ryanodine receptor activator by D. Gordova et al., DuPont Grop Protection, USA. 

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