Antifeedant Potential of Geranylacetone and Nerylacetone and Their Epoxy-Derivatives against Myzus persicae (Sulz.)

Geranylacetone and nerylacetone are natural sesquiterpenoids, which play various roles in plant-insect interactions, including the deterrent and repellent effects on herbivores. The structural modifications of natural compounds often change their biological activities. The aim of the study was to evaluate the effect of geranylacetone, nerylacetone and their epoxy-derivatives on the probing and settling behavior of Myzus persicae (Sulz.) (Hemiptera: Aphididae). The no-choice test using the Electrical Penetration Graph (EPG) technique showed that the probes before the first phloem phase were usually shorter than 3 min, which means that they were terminated within the epidermis and/or outer layers of mesophyll. This resulted in a tendency to delay the initiation of the phloem phase in aphids, which reflects a weak preingestive deterrent activity of the studied compounds at the level of non-vascular tissues. Most M. persicae showed bouts of sustained phloem sap ingestion. However, the 24-h free-choice test demonstrated that aphids did not settle on the leaves treated with geranylacetone, nerylacetone, and their epoxy-derivatives. The refusal to settle after the consumption of phloem sap on treated plants indicated that the studied compounds had postingestive deterrent activity. The epoxidation of geranylacetone and nerylacetone did not evoke significant changes in their activity profiles.

Effect of Soy Leaf Flavonoids on Pea Aphid Probing Behavior

Flavonoids detected in soybean Glycine max (L.) Merr. (Fabaceae) cause various alterations in the metabolism, behavior, and development of insect herbivores. The pea aphid Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae) poses potential threat to soybeans, but the effect of individual flavonoids on its feeding-associated behavior is relatively unknown. We monitored probing behavior (stylet penetration activities) of A. pisum on its preferred host plant, Pisum sativum L. untreated (control) and treated with 0.1% ethanolic solutions of flavonoids apigenin, daidzein, genistein, and kaempferol. We applied the electrical penetration graph (electropenetrography, EPG) technique, which visualizes the movements of aphid stylets within plant tissues. None of the applied flavonoids affected the propensity to probe the plants by A. pisum. However, apigenin enhanced the duration of probes in non-phloem tissues, which caused an increase in the frequency and duration of stylet mechanics derailment and xylem sap ingestion but limited the ingestion of phloem sap. Daidzein caused a delay in reaching phloem vessels and limited sap ingestion. Kaempferol caused a reduction in the frequency and duration of the phloem phase. Genistein did not affect aphid probing behavior. Our findings provide information for selective breeding programs of resistant plant cultivars to A. pisum.

Synthesis of novel phytol-derived γ-butyrolactones and evaluation of their biological activity

The synthesis of phytol-derived γ-butyrolactones as well as their evaluation for deterrent activity towards peach-potato aphid Myzus persicae and antiproliferative activity against four selected cancer cell lines are reported. Products were obtained in good yields (19-96%) and their structures were fully characterized by spectroscopic data (NMR, HRMS). Four synthesized δ-halo-γ-lactones (4-7) are new and have not been previously described in the literature. In the choice test phytol (1) appeared deterrent to M. persicae, whereas modifications of its structure did not cause the avoidance of the treated leaves by the aphids. In contrast, aphids were attracted to the leaves treated with the new trans-δ-chloro-γ-lactone (6). Electrical Penetration Graph (EPG) technique applied to explore the aphid probing and feeding activity revealed that neither phytol nor lactone 6 affected aphid probing and the consumption of phloem sap, which means that both phytol and the lactone 6 might have acted as postingestive modifiers of aphid behavior. The results of in vitro antitumor assays showed that obtained phytol derivatives exhibit cytotoxic activity against studied cancer cell lines (leukemia, lung and colon carcinoma and its doxorubicin resistant subline). Halolactones 4-6 were identified as the compounds, which arrest cell cycle of leukemia cells mainly in G2/M and S phases.

Repellent and Antifeedant Activities of Citral-Derived Lactones against the Peach Potato Aphid

Citral is well known for its antimicrobial, antifungal, and insecticidal activities. Natural sesquiterpene α-methylenelactones also exhibit a broad spectrum of biological activities. The aim of the study was to explore the effect of structural changes to citral molecules on citral behavior-modifying activity towards Myzus persicae. Specifically, the effects of the introduction of a γ-lactone moiety and methylene groups in α and γ positions of the lactone ring were investigated. The lactones were obtained in five-step (saturated lactone and γ-methylenelactone) or six-step (α-methylenelactone and α,γ-dimethylenelactone) syntheses from citral. The synthetic procedures and physical and spectral data of the lactones are presented. The settling behavior of freely moving aphids in choice and no-choice situations was monitored. The probing behavior of tethered M. persicae using the Electrical Penetration Graph (EPG) technique was also analyzed. Citral appeared a strong repellent and pre-ingestive and ingestive probing deterrent to M. persicae. The incorporation of a lactone moiety caused the loss of the repellent activity. α-Methylenelactone inhibited aphid settling and probing activities at pre-ingestive and ingestive phases. The saturated γ-lactone and α,γ-dimethylenelactone were the settling post-ingestive deterrents to M. persicae, which did not affect aphid probing activity. γ-Methylenelactone did not affect aphid behavior.

Effect of Naringenin and Its Derivatives on the Probing Behavior of Myzus persicae (Sulz.)

Substances that alter insect behavior have attracted a lot of attention as potential crop protection agents. Naringenin (5,7,4′-trihydroxyflavanone) is a naturally occurring bioactive flavanone. We evaluated the influence of naringenin on aphid activities during individual phases of probing and feeding and the effect of structural modifications of naringenin on its activity towards aphids. We monitored the probing behavior of Myzus persicae (Sulz.) (Hemiptera: Aphididae) using the Electrical Penetration Graph (EPG) technique. The chemical modifications were the substitution of hydrogen atoms with methyl, ethyl or pentyl groups and the replacement of the carbonyl group in naringenin and its derivatives with an oxime moiety. Depending on the substituents, the activity of naringenin-derived compounds varied in potency and mode of action. Naringenin was an attractant of moderate activity, which enhanced sap ingestion. The naringenin derivative with two methyl groups—7,4′-di-O-methylnaringenin—was a deterrent, which hindered aphid probing in non-phloem tissues. Naringenin oxime derivatives with methyl substituents—7,4′-di-O-methylnaringenin oxime, 7-O-methylnaringenin oxime, and 5,7,4′-tri-O-methylnaringenin oxime—and the derivative with a pentyl substituent—7-O-pentylnaringenin oxime—were strong attractants which stimulated aphid probing in non-phloem tissues and the ingestion of phloem sap.

Cytotoxic, larvicidal, nematicidal, and antifeedant activities of piperidin-connected 2-thioxoimidazolidin-4-one derivatives

The objective of this study was to investigate brine shrimp cytotoxicity, larvicidal, nematicidal, and antifeedant activities of novel piperidin-connected 2-thioxo-imidazolidin-4-one derivatives. The activities of target compounds were compared with some naturally occurring (-)-pinidinol, hydantocidin, and positive controls. Target compounds were synthesized via cyclocondensation method. The compounds were synthesized and then characterized by infrared spectroscopy, 1H NMR, 13C NMR, mass spectral, and elemental analyses. Brine shrimp cytotoxicity assay was investigated using freshly hatched, free-swimming nauplii of Artemiasalina. Larvicidal screening was performed against urban mosquito larvae (Culex quinquefasciatus). Nematicidal activity was evaluated using juvenile nematodes of Meloidogyne javanica. Regarding antifeedant activity, marine-acclimated Oreochromis mossambicus fingerlings were used. Compounds 3a-c (piperidin-connected 2-thioxoimidazolidin-4-one) were found to be lethal to the second instar larvae of mosquito, which produced LD50 values of 1.37, 6.66, 6.51 μg/mL, compared to compounds (-) pinidinol and hyantocidin LD50 values of 18.28 and 22.11 μg/mL respectively. Compound 3a-c was found to kill 100% of fish fingerlings within 6 h at 20 µg/mL, with LD50 values of 1.54, 1.79, 1.52 µg/mL, compared to compounds (-) pinidinol and hyantocidin with LD50 values of 10.21 and 21.05 μg/mL respectively. Compound 3c with LD50 value of 1.57 μg/mL demonstrated high nematicidal activity compared to compound 3a, 3b, (-) Pinidinol and Hyantocidin LD50 values of 6.45, 2.42, 14.25, 26.30 μg/mL respectively. Therefore, the 2-thioxoimidazolidin-4-one with piperidin ring showed high potential cytotoxic, larvicidal, nematicidal, and antifeedent activities.

Antixenosis Potential in Pulses Against the Pea Aphid (Hemiptera: Aphididae)

The aim of the study was to explore the acceptability of 14 species, varieties, and cultivars of grain legumes (Fabales: Fabaceae) to the pea aphid, by investigating the aphid probing behavior using the electrical penetration graph (EPG) technique. Phaseolus coccineus L. 'Felicia', Pisum sativum L. 'Medal', P. sativum arvense (L.) Poir. 'Fidelia' and 'Hubal', and Vicia faba L. 'Dragon' are highly susceptible, with no antixenosis potential against Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae): aphid probing and feeding activities were not impeded. Lathyrus sativus L. 'Derek', Lupinus luteus L.'Perkoz', Vicia faba minor Beck. 'Sonet' are moderately susceptible to A. pisum infestation, with minor antixenosis potential and with antixenosis factors in non-phloem tissues. Aphids on these plants had difficulty to attain the phloem phase and phloem sap ingestion phase. During phloem phase, ingestion lasted for long periods of time. Lens culinaris Medik. 'Green' and Phaseolus vulgaris L. 'Boruta' are moderately susceptible to A. pisum infestation, with minor antixenosis potential and with antixenosis factors in the phloem. Behavior of aphids during pre-phloem phase was similar to that on highly susceptible plants but individual phloem phases and sap ingestion phases were short and contained a high proportion of watery salivation. Glycine max (L.) Merr. 'Aldana', L. angustifolius L. 'Boruta', P. coccineus 'Rothbluende', and P. vulgaris 'Mamut' are highly resistant to A. pisum infestation, with high antixenosis potential and with strong antixenosis factors in non-phloem tissues: aphid probing time was shortened, non-probing intervals between probes were long, and the success rate in reaching phloem phase was very low or none.

Application of Lecitase® Ultra-Catalyzed Hydrolysis to the Kinetic Resolution of (E)-4-phenylbut-3-en-2-yl Esters

The possibility of using Lecitase® Ultra as a novel alternative biocatalyst for the kinetic resolution of model racemic allyl esters of (E)-4-phenylbut-3-en-3-ol: Acetate (4a) and propionate (4b) through their enantioselective hydrolysis was investigated. Reaction afforded (+)-(R)-alcohol (3) and unreacted (−)-(S)-ester (4a or 4b). Hydrolysis of propionate 4b proceeded with higher enantioselectivity than acetate 4a. (R)-Alcohol (3) with highest enantiomeric excess (93–99%) was obtained at 20–30 °C by hydrolysis of propionate 4b, while the highest optical purity of unreacted substrate was observed for (S)-acetate 4a (ee = 34–56%). The highest enantioselectivity was found for the hydrolysis of propionate 4b catalyzed at 30 °C (E = 38). Reaction carried out at 40 °C significantly lowered enantiomeric excess of produced alcohol 3 and enantioselectivity in resolution. Lecitase® Ultra catalyzed the enantioselective hydrolysis of allyl esters 4a,b according to Kazlauskas’ rule to produce (R)-alcohol 3 and can find application as a novel biocatalyst in the processes of kinetic resolution of racemic allyl esters.

Novel Hydroxy- and Epoxy-cis-Jasmone and Dihydrojasmone Derivatives Affect the Foraging Activity of the Peach Potato Aphid Myzus persicae (Sulzer) (Homoptera: Aphididae)

Jasmonates show great potential in sustainable agriculture due to their various roles in natural mechanisms of plant defense, and because they are non-toxic, non-mutagenic, and easily metabolized. The aim of the study was to explore structure⁻activity relationships of dihydrojasmone, cis-jasmone, and their derivatives at the plant⁻aphid interface. We focused on the behavioral responses of aphids, following the exogenous application of natural jasmonates and their derivatives to the host plants. Aphid probing behavior was examined using an electrical penetration graph technique (EPG). The chemoenzymatic transformation of cis-jasmone and the activity of two new derivatives are described. The application of cis-jasmone, dihydrojasmone, the hydroxyderivatives, epoxyderivatives, and alkyl-substituted δ-lactones hindered the foraging activity of Myzus persicae (Sulz.) (Hemiptera: Aphididae) during early stages of probing at the level of non-phloem tissues. The application of saturated bicyclic epoxy-δ-lactone enhanced plant acceptance by M. persicae. Jasmonate derivatives containing a hydroxy group, especially in correlation with a lactone ring, were more active than natural compounds and other derivatives studied. Jasmonates of the present study are worth considering as elements of sustainable aphid control as components of the "push⁻pull" strategy.

Synthesis, Characterization, Cytotoxicity, and Antibacterial Properties of trans-γ-Halo-δ-lactones

A new four-step pathway for the synthesis of γ-halo-δ-lactones is described from simple, commercially available substrates: aryl bromides and 3-methyl crotonaldehyde. The halogenolactonization reaction of β,δ-substituted, γ,δ-unsaturated carboxylic acid 4 a-c is regio- and stereoselective and gives only the trans-isomers of lactones 5 a-c, 6 a-c, and 7 a-c. The structures of all synthesized compounds were confirmed by using spectroscopic methods. For bromolactone, containing a naphthyl moiety in the structure, crystallographic analysis was also performed. The lactones were tested for their cytotoxic activity against L929 cell lines (mouse fibroblasts) and antibacterial activity against Escherichia coli strains ATCC 8739 and Staphylococcus aureus ATCC 65389. Compounds 5 a, 5 c, 7 a, and 7 b statistically significantly inhibited the metabolic activity of mouse fibroblasts L929. Compounds 5 b and 6 a were not cytotoxic towards L929 cells, but showed moderate bactericidal properties.

Biotransformation of Bicyclic Halolactones with a Methyl Group in the Cyclohexane Ring into Hydroxylactones and Their Biological Activity

The aim of this study was the chemical synthesis of a series of halo- and unsaturated lactones, as well as their microbial transformation products. Finally some of their biological activities were assessed. Three bicyclic halolactones with a methyl group in the cyclohexane ring were obtained from the corresponding γ,δ-unsaturated ester during a two-step synthesis. These lactones were subjected to screening biotransformation using twenty two fungal strains. These strains were tested on their ability to transform halolactones into new hydroxylactones. Among the six strains able to catalyze hydrolytic dehalogenation, only two (Fusarium equiseti, AM22 and Yarrowia lipolytica, AM71) gave a product in a high yield. Moreover, one strain (Penicillium wermiculatum, AM30) introduced the hydroxy group on the cyclohexane ring without removing the halogen atom. The biological activity of five of the obtained lactones was tested. Some of these compounds exhibited growth inhibition against bacteria, yeasts and fungi and deterrent activity against peach-potato aphid.

Insect Antifeedant Potential of Xanthohumol, Isoxanthohumol, and Their Derivatives

Xanthohumol (14) and isoxanthohumol (6) derived from hop (Humulus lupulus L., Cannabaceae) and selected chalcone and chromene derivatives, obtained by chemical synthesis, were studied for antifeedant activity against the peach-potato aphid (Myzus persicae [Sulz.]). The study used also commercially available 4-chromanone (1), flavanone (4), naringenin (5), chromone (7), flavone (8), 7-aminoflavone (9), trans-chalcone (10), and 4-methoxychalcone (12). For chromone derivatives it was observed that the presence of a phenyl substituent at C-2 in the chromone (7) skeleton increased the insect antifeedant activity, and this activity was observed for a longer time. Also, the introduction of an amino group at C-7 of flavone (8) considerably increased the insect antifeedant activity, which was observed for the whole test time. Among the compounds examined, the strongest deterrents were isoxanthohumol (6), 7-methoxy-2,2-dimethylchroman-4-one (3), 7-aminoflavone (9), and 4-ethyl-4'-methoxychalcone (13).

Synthesis and Antifeedant Activity of Racemic and Optically Active Hydroxy Lactones with the p-Menthane System

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.

Systemic deterrence of aphid probing and feeding by novel β-damascone analogues

β-Damascone appeared a weak attractant close to not active to Myzus persicae, but modifications of its structure caused the avoidance of treated leaves by aphids during settling and reluctance to probe in simple choice- and no-choice experiments in previous studies. Here, the electrical penetration graph (EPG) technique, which allows monitoring of aphid probing within plant tissues, was applied to explore the biological background and localisation in plant tissues of the deterrent activities of β-damascone and its analogues. Activity of β-damascone and β-damascone-derived compounds depended on their substituents, which was manifested in the variation in the potency of the behavioural effect and differences in aphid probing phases that were affected. β-Damascone appeared a behaviourally inactive compound. The moderately active β-damascone ester affected aphid activities only during the phloem phase. The highly active deterrents-dihydro-β-damascol, β-damascone acetate, δ-bromo-γ-lactone, and unsaturated γ-lactone-affected pre-phloem and phloem aphid probing activities. The most effective structural modification that evoked the strongest negative response from M. persicae was the transformation of β-damascone into δ-bromo-γ-lactone. The behavioural effect of this transformation was demonstrated in frequent interruption of probing in peripheral tissues, which caused repeated failures in finding sieve elements, and reduction in the ingestion time during the phloem phase in favour of watery salivation. The inhibition of aphid probing at both the pre-phloem and phloem levels reveals the passage of the compounds studied through the plant surface and their distribution within plant tissues in a systemic way, which may reduce the risk of the transmission of non-persistent and persistent viruses.

Structure-related antifeedant activity of halolactones with a p-menthane system against the lesser mealworm, Alphitobius diaperinus Panzer

BACKGROUND

Feeding deterrent activity of synthetic halogen lactones against larvae and adults of the lesser mealworm, Alphitobius diaperinus Panzer, in laboratory choice and no-choice tests was studied. The compounds were synthesised from racemic and enantiomerically enriched (ee = 91-98%) cis- and trans-piperitols, which were obtained from (±)-piperitone.

RESULTS

Structure-activity relationship studies identified several synthetic halolactones with a very strong feeding deterrent activity. The most active were the enantiomeric chlorolactones with chiral centre configurations (1S,4S,5R,6R) and (1R,4R,5S,6S) and their racemic mixture. The racemic bromo- and iodolactones obtained from cis-piperitol and saturated lactones with a chiral centre configuration (1R,4S,6R) were also very good antifeedants in comparison with piperitone. Most of the studied compounds were better antifeedants against adults than against larvae-among the 21 compounds, only one bromolactone with a chiral centre configuration (1S,4R,5R,6R) was a weaker deterrent for adults.

CONCLUSION

Chemical transformation of the piperitone molecule by the introduction of a lactone function and a halogen atom strongly changed its antifeedant properties against the lesser mealworm. Optimum activity is dependent on the presence of a chlorine atom at C-5 of the cyclohexane ring. The activity of bromo- and iodolactones depended strongly on the chiral centre configuration and the halogen substituent.

Synthesis of β-damascone derivatives with a lactone ring and their feeding deterrent activity against aphids and lesser mealworms

We report the chemical modification of β-damascone (1) into new lactone derivatives and their biological activity towards aphids and lesser mealworms.

Piperitone-derived saturated lactones: synthesis and aphid behavior-modifying activity

Two racemic and two enantiomeric pairs of new saturated lactones with the p-menthane system were obtained. The lactones were synthesized from racemic and enantiomerically enriched cis- and trans-piperitols, which were obtained from piperitone. The structures of the compounds were confirmed by spectroscopic data. The antifeedant activity of piperitone to Myzus persicae was studied, and the biological consequences of structural modifications of piperitone, that is, lactonization and chiral center configuration, were examined as well. The behavioral responses of M. persicae to piperitone and piperitone-derived saturated lactones were investigated to reveal the biological background of their deterrent activity. Piperitone appeared rather neutral or weakly deterrent to aphids. The introduction of a lactone moiety into a piperitone molecule dramatically changed its biological activity. All piperitone-derived lactones evoked negative aphid responses. However, the deterrent activity of individual compounds varied in potency, the time of expression, and the duration of the effect, depending on the spatial structure of the lactone. Lactones (1R,3S,6R)-3-isopropyl-6-methyl-9-oxabicyclo[4.3.0]nonan-8-one and trans-3-isopropyl-6-methyl-9-oxabicyclo[4.3.0]nonan-8-one showed the broadest ranges and the highest potencies and durabilities of deterrent activity to M. persicae: they acted immediately after application, caused a cessation of probing before aphids reached phloem elements, and decreased the quality of phloem sap.

Lactones 41. Synthesis and microbial hydroxylation of unsaturated terpenoid lactones with p-menthane ring systems

Racemic [(±)-4-isopropyl-1-methyl-7-oxa-cis-bicyclo[4.3.0]non-4-en-8-one] and optically active δ,ε-unsaturated lactones [(-)-(1R,6R)-4-isopropyl-1-methyl-7-oxabicyclo[4.3.0]non-4-en-8-one and (+)-(1S,6S)-4-isopropyl-1-methyl-7-oxabicyclo[4.3.0] non-4-en-8-one)] with the p-menthane system were obtained and their odoriferous properties were evaluated. Biotransformations of the racemic lactone with three fungal strains: Absidia cylindrospora AM336, Absidia glauca AM177 and Syncephalastrum racemosum AM105, were carried out. Microbial transformations afforded hydroxylactones with the hydroxy group in the allylic position.

Synthesis of Sabina δ-Lactones and Sabina δ-Lactams from (+)-Sabinene

Two sabina δ-lactones (3 and 4) were obtained in a two-step synthesis from (+)-sabinene (1). The oxidation of (+)-sabinene (1) with potassium permanganate and sodium periodate to (–)-sabina ketone (2) was the first step. In the second step, the ketone obtained was subjected to chemical and microbial Baeyer–Villiger oxidation. Chemical Baeyer–Villiger oxidation of this ketone afforded two δ-lactones 3 and 4 whereas microbial Baeyer–Villiger oxidation afforded only ‘abnormal’ δ-lactone 4. (–)-Sabina ketone was also the starting material for the synthesis of new δ-lactams (7 and 8). They were obtained by Beckmann rearrangement of sabina ketone oximes 5a and 5b. An attempt to separate (–)-sabina ketone oximes 5a and 5b is also presented.