Abstract
Two racemic and two enantiomeric pairs of new δ-hydroxy-γ-lactones based on the p-menthane system were prepared from racemic and optically active cis- and trans-piperitols. The Johnson-Claisen rearrangement of the piperitols, epoxidation of the γδ-unsaturated esters, and acidic lactonization of the epoxy esters were described. The structures of the compounds were confirmed spectroscopically. The antifeedant activities of the hydroxy lactones and racemic piperitone were evaluated against three insect pests: lesser mealworm, Alphitobius diaperinus (Panzer); Colorado potato beetle, Leptinotarsa decemlineata (Say); and peach-potato aphid, Myzus persicae (Sulz.). The chemical transformation of piperitone by the introduction of a lactone moiety and a hydroxy group changed its antifeedant properties. Behavioral bioassays showed that the feeding deterrent activity depended on the insect species and the structure of the compounds. All hydroxy lactones deterred the settling of M. persicae. Among chewing insects, the highest sensitivity showed A. diaperinus adults.
Highlights
Introduction pMenthane lactones constitute a family of naturally occurring terpenoid compounds
Gas chromatography (GC) analysis was carried out on a 6890N GC instrument equipped with a flame ionization detector (FID) using H2 as the carrier gas and a capillary column (Trace TR-5, 30 m × 0.32 mm × 1.0 μm)
Two racemic and two enantiomerically enriched pairs of new δ-hydroxy-γ-lactones, 6a-c and 11a-c, with the p-menthane system were synthesized from cis- and trans-piperitols, 1a-c (Fig 1) and 7a-c (Fig 2), respectively, which were prepared from (±)-piperitone [28]
Summary
Introduction pMenthane lactones constitute a family of naturally occurring terpenoid compounds. Synthetic lactones with the p-menthane system, in addition to interesting odoriferous attributes [7,8,9], exhibit valuable biological activities such as antifungal [10] and antifeedant properties [11,12,13,14,15,16]. Our interest in terpenoid lactones is inspired mainly by their activity as insect feeding deterrents; many natural antifeedants contain the lactone moiety and have isoprenoid structures [17,18,19,20]. Their low concentrations in plants and their typically complex syntheses have limited the large-scale application of natural antifeedants. In our opinion, synthetic feeding deterrents with simple structures offer better potential for practical use in insect
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