Flubendiamide

Flubendiamide is an example of a new chemical class of insecticides that have been termed phthalic acid diamides (Nauen 2006, Copping and Duke 2007). They are related to the alkaloid ryanodine, which is extracted from Ryania species. Ryanodine affects muscles by binding to calcium channels of the sarcoplasmic reticulum. Ca + ions act as intracellular messengers, and their flux is modulated by calcium channels of this type. The toxic action of ryanodine and synthetic insecticides related to it is due to the disturbance of calcium flux. 

New agrochemicals introduced in the past five years include new chemistries with known modes of action, such as the protoporphyrinogen inhibitor bencarba-zone, the phytoene desaturase picolinafen and beflutamid, and sodium channel pyrethroids new chemistries with possibly new modes of action, such as flonic-amid and pyridalyl and new chemistries with established new modes of actions, such as flubendiamide, which activates ryanodine-sensitive intracellular calcium release channels, ryanodine receptors RyR, in insects. 

DuPont has also introduced a new class of insecticides, the anthranilic diamides, such as DP-23 [205], which, like flubendiamide, also act by activating the ryanodine receptor [206],... 

Flubendiamide is the only member of this class. It is a new insecticide active against lepi-dopterous insects, including those resistant to other classes of insecticides. 

Flubendiamide, a benzenedicarboxamide insecticide, also affects calcium channels. This insecticide induces unique symptomology in poisoned insects, showing a gradual contraction of the insect body. It is believed that flubendiamide induces intracellular Ca2+ release mediated by a calcium channel such as the ryanodine receptor resulting in the contraction of insect muscle (Tohnishi et al., 2005 Ebbinghaus-Kintscher et al., 2006 Nauen, 2006). 

Calcium channels (ryanodine receptor) Ryanodine, flubendiamide, chlorantraniliprole Activation... 

Tohnishi, M., Nakao, H., Furuya, T., Seo, A., Kodama, H., Tsubata, K., Fujioka, S., Kodama, H., Hirooka, T., and Nishimatsu, T., Flubendiamide, a novel insecticide highly active against lepi-dopterous insect pests, /. Pestic. Sci., 30,354, 2005. 

Flubendiamide is a promising new insecticide which is particularly active against lepidopteran pest species and is currently being co-developed by Nihon Nohyaku and Bayer CropScience. It is the first member ofa new chemical class of insecticides named phthalic acid diamides (Figure 5) to be developed. It has been shown to be extremely potent against lepidopterous pests including those resistant... 

II Flubendiamide sulfoxide [3-iodo-N-(2-methanesulfinyl-l,l-dimethyl-ethyl)-N -[2-methyl-4-(l,2,2,2-tetrafluoro-l-trifluoromethyl-ethyl)-phenyl -phthalamide ... 

In further experiments, it was shown that flubendiamide induced a Ca release from internal stores. Flubendiamide evoked Ca transients not only under standard conditions but also when Ca was not included in the application solution. 

This hypothesis was further supported using molecular biology and cellular tools where the insect ryanodine receptor gene was heterologously expressed in appropriate cells. In untransfected CHO cells, application of flubendiamide sulfoxide (a better soluble analogue) did not cause an [Ca ] increase (Figure 8). In CHO cells transfected with the RyR from Drosophila (CHO-RyR), flubendiamide sulfoxide induced Ca responses with similar kinetic responses to those found in Heliothis neurons (Figure 8). 

Therefore it was concluded that flubendiamide acts as a selective activator of the insect ryanodine receptor, inducing ryanodine-sensitive cytosolic Ca transients. Furthermore, radioligand binding studies using microsomal membranes from Heliothis flight muscles demonstrated that flubendiamide allosterically increased the ryanodine affinity. Flubendiamide was found to bind to Heliothis microsomal membranes with an apparent of 4.7 nM. Known ryanodine receptor ligands such as cyclic ADP-ribose, caffeine, ryanodine, and dantrolene did not interfere... 

Figure 9. Effect of caffeine and phthalic diamides on mouse muscle cell line C2C12. representative [Ca ] traces of a Fura2-AM-loaded C2C12 cell during application of caffeine, flubendiamide sulfoxide, and again caffeine.

Figure 10. The Experimental strategy of the elucidation of the novel mode of action of flubendiamide is a good example for a successful integration and application of different disciplines as well as of cutting edge technologies in the research process.

Flubendiamide has been presented in this talk as an example for this approach. This molecule is the hrst representative of a new chemical class of insecticides... 

The evaluation of the mode of action of flubendiamide is a result of the joint efforts of Nihon Nohyaku and Bayer CropScience researchers Ulrich Ebbinghaus-Kintscher, Rudiger Fischer, Peter Liimmen, Klaus Raming (BCS) and Takao Masaki, Noriaki Yasokawa, Masanori Tohnishi (Nihon Nohyaku). 

Agricultural Research, Technology Portfolio, Tools, Discovery Platform, Mode of Action, Flubendiamide, Ryanodine Receptor... 

Flubendiamide, a New Insecticide Characterized by Its Novel Chemistry and Biology... 

Resistance has often been a problem or a potential problem for insecticides and this is one of the most important reasons why the insecticides with a new mode of action have been always desired, though it is quite a difficult task to find such molecules. Flubendiamide, discovered by Nihon Nohyaku (NNC), is a novel insecticide belonging to the new chemical class of 1,2-benzenedicarboxamides or phfhalic diamides, having a unique chemical structure (Figure 1) [1-3], Flubendiamide is co-developed by NNC and Bayer CropScience globally [4], The structure-activity relationships, the chemistry, including topics in process research, the mode of action and the biological profiles are described. 

Figure 1. The chemical structure of flubendiamide, 3-iodo-N -(2-mesyl-l, 1 -dimethylethyl)-N- 4-[l, 2,2,2-tetrafluoro-l -(trifluoromethyl)ethyl]-o-tolyl phthalamide.

Figure 2 shows the early phase of research for flubendiamide. In 1989, Dr. T. Tsuda, at Osaka Prefecture University in Japan, reported that some pyrazinedicarbox-amide derivatives showed moderate herbicidal activity [5]. From 1990, the research for herbicide discovery was conducted at NNC Research Center. In the course of this research, a lead compound for an insecticide was discovered in 1993 from the class of benzenedicarboxamides as shown in Figure 2. This compound provided insecticidal activity on lepidoptera at the relatively high dose of 50-500 mg a.i./L. Moreover, it did not show activity against other species such as Hemiptera or Aca-rina. Although the level of activity was not satisfactory, this compound attracted the attention of researchers for both the novelty of its chemical structure and the characteristic insecticidal symptoms such as gradual contractions of the insect body. We therefore started the study for further optimization of this lead compound.

The weak insecticidal activity was found in the lead compound its structure was quite new as an insecticide. However, there were various points to be improved for practical use such as increased insecticidal activity, reduced phytotoxicity to crops and instability of the compound. Two thousand derivatives were synthesized with the general formula shown in Figure 3. Many studies on the improvement of the activity were conducted, and flubendiamide was finally discovered in 1998. 

The last section shows the effect of substituents (Rj, R2) on the aliphatic amide moiety. As for the aliphatic side chain, it was found that the alpha-branched alkyl side chain was essential for stabilizing the diamide structure. In the case of non-branched alkyl, the diamide derivatives tend to decompose to the corresponding phfhalimides. A variety of substituents were examined to improve the activity. As shown in Table I, the introduction of a heteroatom or a functional group increased the insecticidal activity especially a sulfur atom within the alkyl side chain markedly increased the activity. This sulfonylalkylamine is also novel as an amine residue in pesticide chemistry. In summary, flubendiamide has unique substituents as essential parts of the structure in three adjacent positions on the benzene ring, which characterizes the chemical structare of flubendiamide as totally novel. 

Figure 4. Synthetic pathway of flubendiamide at the early optimization stage.

Flubendiamide is most effective on larvae followed by adults, but it has no ovicidal activity. In the course of extensive research on the mode of action of flubendiamide, it was determined that flubendiamide was a ryanodine receptor modulator. Flubendiamide Axes the Ca-channel of insect ryanodine receptors (RyR) in the open state, and subsequently induces calcium release from the membrane vesicle... 

Table II shows the insecticidal activity of flubendiamide against major insect and acarina species. Flubendiamide provided high activity on all lepidopterous insect pests, and its ECjq values were between 0.004 and 0.58 mg a.i./L. However, flubendiamide did not show activity against other insect species. Thus, the insecticidal spectrum of flubendiamide is expected to be broad among lepidoptera pests in agriculture. Against the resistant strain of diamondback moth, flubendiamide provided the same level of activity as against the susceptible strain. This result indicates that flubendiamide will be useful for insecticide resistance management (IRM) programs.

Table III shows the activity of flubendiamide on several species of beneficial arthropods and natural enemies. Flubendiamide was inactive against beneficial arthropods (except silkworm) and natural enemies tested. This result indicates that flubendiamide should be very safe for natural enemies, and consequently will fit well into integrated pest management (IPM) programs.

Field evaluations of flubendiamide have been conducted in many areas on various crops such as vegetables, top fruits, and cotton. Flubendiamide shows excellent performance on controlling the major lepidopterous pests in the field at the recommended dose and its efficacy was better than those of standard insecticides. Furthermore, flubendiamide (20% WDG) showed no phytotoxicity to vegetables, tea and top-fruits at recommended doses [3-4],... 

Table III. Activity of flubendiamide on beneficiai arthropods and natural enemies.

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