Shaiene Costa Moreno

Synthesis and insecticidal activity of new pyrethroids.

BACKGROUND Pyrethroids are among the most potent pesticides known, with great potential for structural variation with retention or enhancement of potency. The simple methyl ester is easier to prepare (at least one step shorter) than the more complex pyrethroids modified on the alcohol moiety. The objective was to synthesise methyl esters of pyrethroid acids containing an aromatic ring on the acid moiety and evaluate their biological activity against Ascia monuste orseis Latr., Tuta absoluta Meyrick, Periplaneta americana (L.), Musca domestica L. and Sitophilus zeamais (Motsch.). RESULTS The synthetic sequence required seven steps: protection of the hydroxyl groups of D-mannitol, diol oxidative cleavage with sodium metaperiodate, alkene formation by Wittig reaction with methoxycarbonylmethylidene(triphenyl)phosphorane, cyclopropanation, acetal hydrolysis with perchloric acid and oxidative cleavage with sodium metaperiodate gave methyl (1S, 3S)-3-formyl-2,2-dimethylcyclopropane-1-carboxylate. The final step comprised reaction of the aldehyde with five different aromatic phosphorus ylides to give the pyrethroids. CONCLUSION An efficient and versatile synthesis of ten new pyrethroid methyl esters has been accomplished from the readily available D-mannitol in seven steps. All compounds showed insecticidal activity, and methyl (1S, 3S)-3-[(Z)-2-(4-chlorophenyl)vinyl]-2,2-dimethylcyclopropane-1-carboxylate was the most active, killing 90% of A. monuste orseis and 100% of T. absoluta and P. americana.

New Pyrethroids for Use Against Tuta Absoluta (Lepidoptera: Gelechiidae): Their Toxicity and Control Speed

Abstract Insect pests are responsible for major losses in crop productivity, and insecticides are the main tools used to control these organisms. There is increasing demand for new products for pest management. Therefore, the aim of this study was to assess the toxicity of pyrethroids with acid moiety modifications to measure the insecticidal activity of these compounds on Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae). First, we synthesized E/Z mixtures of five pyrethroids: [9], [10], [11], [12], and [13]. Then, we separated the cis and trans pyrethroid isomers of [9], [10], [11], and [12]. We assessed the toxicity of these compounds against T. absoluta. The E/Z mixtures of the five pyrethroids (30 µg of substance per mg−1 of insect) caused high (100%) and rapid (<12 h) tomato borer mortality. The cis isomer of pyrethroid [10] was the most toxic to T. absoluta, causing mortality similar to permethrin. The other isomers were less powerful than permethrin.

Toxicity of new pyrethroid in pest insects Asciamonuste and Diaphania hyalinata, predator Solenopsis saevissima and stingless bee Tetragonisca angustula

ABSTRACT There is increasing demand for new products for vegetable pest management. Thus, the aim of this study was to assess the toxicity of pyrethroids with acid moiety modifications to measure the insecticidal activity of these compounds on the lepidopteran vegetable pests Diaphania hyalinata (L.) (Lepidoptera: Pyralidae) and Asciamonuste (Latreille) (Lepidoptera: Pieridae) and evaluate their selectivity for the predatory ant Solenopsis saevissima (F. Smith) (Hymenoptera: Formicidae) and pollinator Tetragonisca angustula (Latreille) (Hymenoptera: Apidae: Meliponinae). Racemic mixtures of five new pyrethroids (30 µg molecule mg−1 insect body weight) resulted in high (100%) and rapid (stable LD50 after 12 h) mortality in D. hyalinata and A. monuste. In A. monuste, the trans-pyrethroid [12] isomer showed similar toxicity to permethrin. For D. hyalinata, the trans-pyrethroid [9] isomer and cis-pyrethroid [10] isomer were as toxic as permethrin. Due to their low selectivity, these new pyrethroids should be applied on the basis of ecological selectivity principles to minimize impacts on nontarget organisms S. saevissima and T. angustula.