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Molecules 2019, 24(6), 1023; https://doi.org/10.3390/molecules24061023

Synthesis and Stereostructure-Activity Relationship of Novel Pyrethroids Possessing Two Asymmetric Centers on a Cyclopropane Ring

Department of Chemistry, School of Science and Technology, Kwansei Gakuin University, 2-1 Gakuen, Sanda, Hyogo 669-1337, Japan
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Received: 14 February 2019 / Revised: 7 March 2019 / Accepted: 9 March 2019 / Published: 14 March 2019
(This article belongs to the Section Organic Chemistry)
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Abstract

2-Methylcyclopropane pyrethroid insecticides bearing chiral cyanohydrin esters or chiral ethers and two asymmetric centers on the cyclopropane ring, were synthesized. These compounds were designed using a “reverse connection approach” between the isopropyl group in Fenvalerate, and between two dimethyl groups in an Etofenprox analogue (the methyl, ethyl form), respectively. These syntheses were achieved by accessible ring opening reactions of commercially available (±)-, (R)-, and (S)-propylene oxides using 4-chlorobenzyl cyanide anion as the crucial step, giving good overall yield of the product with >98% ee. The insecticidal activity against the common mosquito (Culex pipiens pallens) was assessed for pairs of achiral diastereomeric (1R*,2S*)-, (1R*,2R*)-cyanohydrin esters, and (1R*,2S*)-, (1R*,2R*)-ethers; only the (1R*,2R*)-ether was significantly effective. For the enantiomeric (1S,2S)-ether and (1R,2R)-ether, the activity was clearly centered on the (1R,2R)-ether. The present stereostructure‒activity relationship revealed that (i) cyanohydrin esters derived from fenvalerate were unexpectedly inactive, whereas ethers derived from etofenprox were active, and (ii) apparent chiral discrimination between the (1S,2S)-ether and the (1R,2R)-ether was observed. During the present synthetic study, we performed alternative convergent syntheses of Etofenprox and novel 4-EtO-type (1S,2S)- and (1R,2R)-pyrethroids from the corresponding parent 4-Cl-type pyrethroids, by utilizing a recently-developed hydroxylation cross-coupling reaction. View Full-Text
Keywords: pyrethroid; structure‒activity relationship; asymmetric synthesis; cyclopropane formation; two asymmetric centers; common mosquito; chiral discrimination; hydroxylation cross-coupling reaction; fenvalerate; etofenprox pyrethroid; structure‒activity relationship; asymmetric synthesis; cyclopropane formation; two asymmetric centers; common mosquito; chiral discrimination; hydroxylation cross-coupling reaction; fenvalerate; etofenprox
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Taniguchi, T.; Taketomo, Y.; Moriyama, M.; Matsuo, N.; Tanabe, Y. Synthesis and Stereostructure-Activity Relationship of Novel Pyrethroids Possessing Two Asymmetric Centers on a Cyclopropane Ring. Molecules 2019, 24, 1023.

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