Juraj Harmatha

Chromatographic procedures for the isolation of plant steroids

In this review, we consider the general principles and specific methods for the purification of different classes of phytosteroids which have been isolated from plant sources: brassinosteroids, bufadienolides, cardenolides, cucurbitacins, ecdysteroids, steroidal saponins, steroidal alkaloids, vertebrate-type steroids and withanolides. For each class we give a brief summary of the characteristic structural features, their distribution in the plant world and their biological effects and applications. Most classes are associated with one or a few plant families, e.g., the withanolides with the Solanaceae, but others, e.g., the saponins, are very widespread. Where a compound class has been extensively studied, a large number of analogues are present across a range of species. We discuss the general principles for the isolation of plant steroids. The predominant methods for isolation are solvent extraction/partition followed by column chromatography and thin-layer chromatography/HPLC.

Biological activities of lignans and stilbenoids associated with plant-insect chemical interactions

Lignans and biogenetically-related secondary metabolites derived from phenylpropanoid precursors play a significant role in the defence of plants against insects. They act largely as regulators of insect feeding, but in a few cases they can influence also specific physiological functions of insects. The antifeedant activities of a series of lignans are summarised and compared with previously published data. The compounds represent either natural substances isolated from plants or their chemically transformed structural analogues. The precise mode of action of such compounds is mostly unknown. One possible mechanism might be interaction with, and disruption of, the endocrine system, which is crucial for proper development of insects and is dependent on the action of moulting hormones (ecdysteroids). This hypothesis has been tested using the specific Drosophila melanogaster BII cell line bioassay for ecdysteroid agonists and antagonists, in which the potency of the test compound reflects the affinity of binding to the ligand-binding site of the D.xa0melanogaster ecdysteroid receptor. The activity data are evaluated in terms of a structure-activity relationship. To explore this phenomenon, the compounds were prepared and tested alongside ecdysteroid analogues and some insect ecdysis/metamorphosis-disturbing steroidal and non-steroidal natural compounds. Several phenylpropanoids, including lignans and stilbenoids (derived from resveratrol), were evaluated with promising results. The results indicate that such phenylpropanoid-derived compounds can possess ecdysteroid antagonistic activity, which could potentially influence insect development.

Comparison of the feeding deterrent activity of some sesquiterpene lactones and a lignan lactone towards selected insect storage pests

Four sesquiterpene lactones isolated from Eurpatorium cannabinum, Homogyne alpina and Petasites albus (all Compositae), together with two of their adducts, as well as one lignan lactone of dibenzylbutanolide type from Libocedrus yateensis (Cupressaceae), were tested for their feeding deterrent activity against the adults of Sitophilus granarius and Tribolium confusum, as well as against the larvae of Tribolium confusum and Trogoderma granarium. The strongest deterrent activity against all species was exhibited by the lignan lactone yatein and the sesquiterpene spirolactone bakkenolide A. Both may be included to the class of very good insect feeding deterrents. The comparison presented here showed that the conjugated α-exomethylene moiety of the lactone ring was not the decisive factor for the deterrent activity in the investigated test model.

Insect feeding deterrent activity of lignans and related phenylpropanoids with a methylenedioxyphenyl (piperonyl) structure moiety

The antifeedant activity of a series of lignan lactones, hemiacetals, ethers, and alcohols derived from yatein and cubebin, together with structurally related phenylpropanoids and phenolics possessing a methylenedioxyphenyl (piperonyl) moiety, was tested against selected stored products pests: Sitophilus granarius L. (Coleoptera: Curculionidae), Tribolium confusum Duv. (Coleoptera: Tenebrionideae), and Trogoderma granarium Ev. (Coleoptera: Dermestridae). The relation between molecular structure and antifeedant activity was examined and implication of the piperonyl moiety is assessed. The compounds represent either natural substances isolated from plants (Libocedrus yateensis Guillaumin and Piper cubeba L.) or their structural analogues prepared by simple chemical transformations as well as compounds selected from commercially available sources. Natural lignan lactones with methoxy and/or methylenedioxy substituents showed significant activity that is strong enough to affect plant ‐ insect interactions. Presence of polar substituents, especially hydroxy or glycosyl groups, often reduce the activity. Non‐polar substituents, such as methoxy or methylenedioxy groups, enhance the activity not only in lignans but also in simple phenylpropanoids. The most active compound was synthetic piperonylbutoxide.

Effects of pyrrolizidine alkaloids and sesquiterpenes on snail feeding

SummaryWe determined in the laboratory the feeding response of two populations of the generalist herbivorous snail Arianta arbustorum (Helicidae) towards the composite Adenostyles alliariae and towards various allelochemicals. These were: a pyrrolizidine alkaloid (PA) extract of Adenostyles leaves; senecionine (a PA present in Adenostyles); retrorsine (a PA not present in Adenostyles) and two sesquiterpene (ST) fractions from Adenostyles: a mixture of the STs adenostylone and neoadenostylone, and deacyladenostylone. Tertiary PAs and PA N-oxides were tested separately. For each allelochemical, we tested whether it was deterrent or whether it induced changes of feeding behaviour (i.e. whether it had pre- or postingestive effects), and whether the effects were more pronounced with younger (smaller) snails. The tertiary PA extract from Adenostyles was deterrent, especially for young snails, but did not induce changes of feeding behaviour. Tertiary PA senecionine was deterrent for young snails only and induced changes of feeding behaviour. Also, consumption of untreated Petasites was higher after this treatment. Tertiary PA retrorsine was not deterrent, but induced changes of feeding behaviour. The PA N-oxides showed no activity against the snails. The mixture of adenostylone and neoadenostylone was deterrent and induced feeding aversions. Deacyladenostylone was highly deterrent, but did not induce changes of feeding behaviour. At the Jura site, PA content of Adenostyles was lower than at the Black Forest site. The snails from Jura consumed much less Adenostyles than the snails from Black Forest, and also ate a little less of the treated leaf discs. The PAs which are encountered by the snails in their natural food plants (PA extract and senecionine) were more deterrent than retrorsine (a novel compound). This suggests that the snails have mechanisms for the rejection of allelochemicals which they encounter in their natural food plants, but not for novel allelochemicals. The results suggest two hypotheses regarding the function of the allelochemicals in Adenostyles: (1) The allelochemicals act mainly on very young snails. (2) PAs render Adenostyles toxic, while STs act as feeding deterrents.

Ecdysteroids from the roots of Leuzea carthamoides

Abstract Three new ecdysteroids: polypodine B 20,22-acetonide, 20-hydroxy-ecdysone 2,3;20,22-diacetonide and isovitexirone along with 20-hydroxyecdysone, 20-hydroxyecdysone 2,3-acetonide, 20-hydroxyecdysone 20,22-acetonide, ajugasterone C, makisterone A and polypodine B were isolated from the roots of Leuzea carthamoides.

Biological activity of natural and synthetic ecdysteroids in the B11 bioassay

The potencies of 19 ecdysteroids are compared in the BII bioassay, which reflects the affinity of binding to the ligand binding site of the Drosophila melanogaster ecdysteroid receptor. The compounds tested represent either natural products isolated from plants (phytoecdysteroids) or fungi (mycoecdysteroids) or synthetic analogues based on insect metabolites (zooecdysteroids). None of the tested compounds showed any antagonistic activity, but all possessed quantifiable agonistic activity. All the mycoecdysteroids were less potent than the major insect ecdysteroid, 20-hydroxyecdysone (20E). Also, conjugation of 20E with a glucose moiety results, as expected, in considerable reduction in biological activity, but the remaining activity is dependent on the position of conjugation. The implications of these findings for the structure/activity relationship of ecdysteroids are discussed.

Ecdysteroid constituents of the mushroom Tapinella panuoides

Abstract Ecdysteroids, compounds structurally related to the insect moulting hormone ecdysone, were isolated from the mushroom Tapinella panuoides . Paxillosterone and two further new ergostane-type ecdysteroids, panuosterone and 25-hydroxypanuosterone, together with the already known cholestane-type ecdysteroids, 20-hydroxyecdysone, ponasterone A, malacosterone and turkesterone were identified by NMR, IR and mass spectrometric methods. The taxonomic value of ecdysteroids for chemosystematics in fungi and particularly in the genera Paxillus and Tapinella , is discussed.

Phenolic and terpenoid heartwood constituents of Libocedrus yateensis

Abstract The heartwood of Libocedrus yateensis has been found to contain cumic acid and several related hydroxyacids so far not reported from any conifer, a sesquiterpene (−)-cryptomerione and (E, E)-1,4-bis-(p-hydroxyphenyl)-buta-1,3-diene, both known from Taxodiaceae. Further constituents were ‘conioids’; hinokiresinol and a related ketone, probably dehydroagatharesinol, a lignan, ‘yatein’, and a novel diphenylbutane derivative, yateresinol. Structural relations between conioids, lignans and diphenylbutanes are discussed.

Additional minor ecdysteroid components of Leuzea carthamoides

Seventeen additional minor ecdysteroid compounds were isolated and identified from the roots of Leuzea carthamoides (Wild.) DC. Eight of them are new phytoecdysteroids: carthamoleusterone (13) is a new side-chain cyclo-ether with five-membered ring; 14-epi-ponasterone A 22-glucoside (12) is a rare and unusual natural 14 beta-OH epimer; 15-hydroxyponasterone A (11) is also new and rare with its C-15 substituted position, as well as 22-deoxy-28-hydroxymakisterone C (18) possessing secondary hydroxyl in position C-28 and 26-hydroxymakisterone C (20) with hydroxy groups in positions 25 and 26. New are also 1 beta-hydroxymakisterone C (21) and 20,22-acetonides of inokosterone (8) and integristerone A (10). Series of already known ecdysteroids: ecdysone (1), 20-hydroxyecdysone 2- and 3-acetates (3 and 4), turkesterone (6), inokosterone (7), 24-epi-makisterone A (14), and amarasterone A (22) are reported here as new constituents of L. carthamoides. Seven earlier reported Leuzea ecdysteroids: 20-hydroxyecdysone (2), ajugasterone C (5), integristerone A (9), 24(28)-dehydromakisterone A (15), 24(28)-dehydroamarasterone B (16), (24Z)-29-hydroxy-24(28)-dehydromakisterone C (17) and makisterone C (19) are also included because they are now better characterized.