Samir A. M. Abdelgaleil

Khayanolides, rearranged phragmalin limonoid antifeedants from Khaya senegalensis

Abstract Three new rearranged phragmalin-type limonoids, named khayanolides A, B and C, were isolated as insect antifeedant together with four known rings B,D-seco compounds, seneganolide, methyl angolensate and its 6-hydroxy and 6-acetoxy derivatives from the ether extract of the stem bark of Khaya senegalensis. The structure of new compounds was elucidated by spectroscopic means and the absolute structure of khayanolide A was established by X-ray analysis and CD study. The antifeedant activity of the isolated compounds was also reported.

Insecticidal and synergistic effects of Majorana hortensis essential oil and some of its major constituents

The essential oil from leaves of Majorana hortensis Moench (Lamiaceae) was isolated by hydrodistillation with a yield of 1.6% (wt/wt). The insecticidal activity of the oil was evaluated against fourth instars of Spodoptera littoralis Boisduval (Lepidoptera: Noctuidae) and adults of Aphis fabae L. (Hemiptera: Aphididae). The oil showed a remarkable toxic effect against S. littoralis in a topical application assay (LD50 = 2.48 μg per larva) and in a residual film assay (LC50 = 3.14 g/l). The oil of M. hortensis also exhibited a pronounced toxic effect against A. fabae adults with LC50 values of 1.86 and 2.27 g/l in rapid dipping and residual film assays, respectively. Gas chromatography‐mass spectrometry analyses of M. hortensis essential oils revealed the presence of 31 compounds and the main components were terpinen‐4‐ol (30.0%), γ‐terpinene (11.3%), and trans‐sabinene hydrate (10.8%). Repeated column chromatography of M. hortensis oil on silica gel led to the isolation of two major constituents, which were characterized based on 1H‐nuclear magnetic resonance and mass spectrometric data, as terpinen‐4‐ol and γ‐terpinene. These two components were examined for their insecticidal and synergistic activities towards S. littoralis and A. fabae. Terpinen‐4‐ol and γ‐terpinene exhibited a significant insecticidal activity against both insects, but γ‐terpinene was more toxic than terpinen‐4‐ol. When tested in a binary mixture with the synthetic insecticides profenofos and methomyl, it was found that both compounds enhanced the insecticidal activity of these insecticides by two‐ to threefold. These results show that terpinen‐4‐ol and γ‐terpinene have a synergistic effect on the insecticidal activities of synthetic insecticides profenofos and methomyl.

Khayanolides A and B, new rearranged phragmalin limonoid antifeedants from Khaya senegalensis

Abstract Khayanolides A and B, two new rearranged phragmalin limonoids, were isolated as insect antifeedants together with two known rings B,D-seco compounds, methyl angolensate and its 6-hydroxy derivative from the ether extract of the stem bark of Khaya senegalensis. The structure of the new compounds was elucidated by spectroscopic means and the absolute structure of khayanolide A was established by X-ray analysis and CD study. The antifeedant activity is also reported.

Diterpenoids from Euphorbia paralias

Two segatane diterpenoids containing a bicyclic [4,3,1] ring system were isolated, together with 11 known diterpenoids, four segetanes, five jatrophanes and two paralianes, from the aerial parts of Euphorbia paralias. The structures of the new compounds were established by spectroscopic means, including by 2D NMR and CD spectroscopic analyses. The antifeedant and antiviral activities of the isolated compounds are also described.

Effect of some essential oils on in vitro methane emission

The objectives of this study were to characterise four essential oils (EO) chemically and to evaluate their effect on ruminal fermentation and methane emission in vitro. The investigated EO were isolated from Achillea santolina, Artemisia judaica, Schinus terebinthifolius and Mentha microphylla, and supplemented at four levels (0, 25, 50 and 75 μl) to 75 ml of buffered rumen fluid plus 0.5 g of substrate. The main components of the EO were piperitone (49.1%) and camphor (34.5%) in A. judaica, 16-dimethyl 15-cyclooactdaiene (60.5%) in A. santolina, piperitone oxide (46.7%) and cis-piperitone oxide (28%) in M. microphylla, and γ-muurolene (45.3%) and α-thujene (16.0%) in S. terebinthifolius. The EO from A. santolina (at 25 and 50 μl), and all levels of A. judaica increased the gas production significantly, but S. terebinthifolius (at 50 and 75 μl), A. santolina (at 75 μl) and all levels of M. microphylla decreased the gas production significantly in comparison with the control. The highest levels of A. santolina and A. judaica, and all doses from M. microphylla EO inhibited the methane production along with a significant reduction in true degradation of dry matter and organic matter, protozoa count and NH3-N concentration. It is concluded that the evaluated EO have the potential to affect ruminal fermentation efficiency and the EO from M. microphylla could be a promising methane mitigating agent.

Evaluation of antibacterial properties and biochemical effects of monoterpenes on plant pathogenic bacteria

The antibacterial activity of twelve monoterpenes, namely camphene, (R)-camphor, (R)-carvone, 1,8cineole, cuminaldehyde, (S)-fenchone, geraniol, (S)-limonene, (R)-linalool, (1R,2S,5R)-menthol, myrcene and thymol was tested against two plant pathogenic bacteria Agrobacterium tumefaciens and Erwinia carotovora var. carotovora using agar dilution method. For a better understanding of monoterpenes mechanisms of action, the inhibitory effect of three monoterpenes (R)-linalool, myrcene and thymol was assessed on dehydrogenases and polyglacturonase activities. Among the tested monoterpenes, thymol, (S)limonene and myrcene were the most potent antibacterial compounds against A. tumefaciens with minimum inhibitory concentration (MIC) of 1000 mg/L. Thymol was also the most effective compounds against E. carotovora var. carotovora, while camphene, cunimaldhyde and 1,8-cineole were the less effective compounds against both bacteria. In biochemical studies, myrcene caused the highest inhibitory effect on dehydrogenases activity of the two tested bacteria, followed by thymol. However, thymol showed the highest inhibitory effect on polygalacturonase activity of both tested bacteria, followed by (R)-linalool. In general, there was a positive correlation between the antibacterial activity of monoterpenes and their inhibitory effects on both enzymes. This is the first report for the determination of MIC and enzymes inhibitory effects of tested monoterpenes on plant pathogenic bacteria.

Antifungal and biochemical effects of pseudoguaianolide sesquiterpenes isolated from Ambrosia maritima L.

Five pseudoguaianolide sesquiterpenes, namely neoambrosin, damsinic acid, damsin, ambrosin and hymenin isolated from the aerial parts of Ambrosia maritima, were tested for their antifungal activity against the most economic plant pathogenic fungi Botrytis cinerea and Fusarium oxysporum which cause grey mold and root rot diseases, respectively. In mycelial radial growth inhibition assay, neoambrosin and damsin were the most potent, while hymenin and damsinic acid were the lowest effective among the tested compounds. F. oxysporum was more sensitive for inhibition than B. cinerea. On the other hand, the sesquiterpenes caused significant reduction in spore germination of both fungi at 50, 100 and 200 mg/L compared with the control. Complete inhibition was observed when the spores treated with damsinic acid and ambrosin at 200 mg/L. In vivo activities of polyphenol oxidase, polygalacturonase and pectin-lyase in both fungi that treated with 0.5 and 1 fold of the EC50 value were also carried out in order to investigate the biochemical influences of the tested compounds. The compounds showed significant inhibitory effects on the enzyme activities compared with the control however; the activity was not consistently related to the in vitro inhibitory effects.

Insecticidal properties of essential oils against Tribolium castaneum (Herbst) and their inhibitory effects on acetylcholinesterase and adenosine triphosphatases

Essential oils from 20 Egyptian plants were obtained by using hydrodistillation. The chemical composition of the isolated oils was identified by gas chromatograph/mass spectrometer. Fumigant and contact toxicities of the essential oils were evaluated against the adults of Tribolium castaneum. In fumigation assays, the oil of Origanum vulgare (LC50 = 9.97 mg/L air) displayed the highest toxicity towards the adults of T. castaneum. In contact assays, the oils of Artemisia monosperma (LC50 = 0.07 mg/cm2) and O. vulgare (LC50 = 0.07 mg/cm2) were the most potent toxicants against the adults of T. castaneum. Biochemical studies showed that the tested oils caused pronounced inhibition of acetylcholinesterase (AChE) and adenosine triphosphatases (ATPases) isolated from the larvae of T. castaneum. The oil Cupressus macrocarpa (IC50 = 12.3 mg/L) was the most potent inhibitor of AChE, while the oil of Calistemon viminals (IC50 = 4.4 mg/L) was the most potent inhibitor of ATPases.

Rings B,D-seco limonoid antifeedants from Swietenia mahogani.

Three phragmalin-type limonoids, swietephragmin H (1), swietephragmin I (2) and 11-hydroxyswietephragmin B (3), and a mexicanolide-type limonoid 2-hydroxy-6-deacetoxyswietenine (4), together with known compounds, 6-O-acetyl-2-hydroxyswietenin (5), 2-hydroxyswietenine (6), swietemahonin G (7), methyl 6-hydroxyangolensate (8) and 7-deacetoxy-7-oxogedunin (9) were isolated from the leaves of Swietenia mahogani (Meliaceae). Their structures were established by extensive NMR experiments in conjunction with mass spectrometry. The antifeedant activity of the isolated compounds was evaluated.

PRE and POST Herbicidal Activity of Monoterpenes against Barnyard Grass (Echinochloa crus-galli)

Abstract Monoterpenes, the major constituents of essential oils, are known for their diverse biological activities. This study was conducted to assess the herbicidal effect of six monoterpenes viz. (R)-carvone, 1,8-cineole, cuminaldehyde, (S)-fenchone, geraniol, (S)-limonene, and (R)-linalool on barnyardgrass under laboratory and glasshouse conditions with a view to explore the possibility of their utilization for future weed management. The effect of monoterpenes on chlorophyll contents and total phenolic compounds was also evaluated. The inhibitory effects of monoterpenes on seed germination and seedling growth were tested at concentrations of 1, 2, 4, 6, and 8 mM. The results showed that geraniol and (R)-carvone caused greatest reduction of seed germination with complete inhibition at the concentrations > 2 mM. Similarly, these two compounds were the most potent inhibiters for root and shoot growth. In general, monoterpenes were less effective against seed germination than seedling growth. Furthermore, the inhibition of root growth by all compounds was greater than that of shoot growth. In foliar application treatments under glasshouse conditions, the monoterpenes reduced the fresh and dry weights, and shoot length of two-leaf stage barnyardgrass at concentrations of 1 and 2%. In addition, the tested monoterpenes caused phytotoxicity symptoms, mainly chlorosis and necrosis, followed by weed death. Complete weed control was observed in the treatments with 1 and 2% of geraniol, and 2% of cuminaldehyde. Further, a reduction of chlorophyll contents and total phenolic compounds of barnyardgrass leaves was noticed, indicating that the monoterpenes cause adverse effect on photosynthesis and weed metabolism. Based on the results of this study, it can be concluded that the monoterpenes, particularly geraniol, (R)-carvone, and cuminaldehyde, can be used as potential natural herbicides. Nomenclature: Barnyardgrass, Echinochloa crus-galli (L.) Beauv., (R)-carvone, 1-8-cineole, cuminaldehyde, (S)-fenchone, geraniol, (S)-limonene, (R)-linalool.