Anna K. Picman

Biological activities of sesquiterpene lactones

Abstract Although sesquiterpene lactones are terpenoid compounds characteristic of the Asteraceae (Compositae) they are also known from other angiosperm families as well as from some gymnosperms. The wide variety of chemical structures so far discovered is matched by a diversity of biological activities. Compounds that have cytotoxic, anti-tumourgenic, anti-bacterial and anti-fungal properties are widely distributed. Various sesquiterpene lactones are known to be toxic to human and animal parasites, insects and vertebrates. Many of these compounds or plants containing them are a cause of allergic contact dermatitis in humans but some of them have been used for their pharmacological activity. Sesquiterpene lactones also act as plant growth regulators and are responsible for allelopathic properties of many plants. Various activities of sesquiterpene lactones suggest their evolutionary significance in plants as deterrents against herbivores and anti-fungal, anti-bacterial allelopathic agents. This review summarizes the present knowledge regarding the biological activities of sesquiterpene lactones and their structure-activity relationships.

Autotoxicity in Parthenium hysterophorus and its possible role in control of germination

Abstract The autotoxic effect of water soluble secondary plant metabolites, sesquiterpene lactones and phenolic acids present in the aggressive weed Parthenium hystrophorus were examined. It was found that the germinaion rates of achenes of P. hysterophorus increased with increasing distance between them (decreasing achene density) and increasing washing period preceding the germination trials. The inhibition of germination processes by water soluble autotoxins is temporary and its duration is determined by the concentration of autotoxins in the environment. Sesquiterpene lactones, parthenin and coronopilin, which are present in large amounts in P. hysterophorus, are autotoxic to seedlings and older plants at a concentration of 0.1%. It is suggested that in P. hysterophorus, the water soluble plant metabolites play an important role not only in allelopathy and defense against herbivorous predators and diseases but also as autotoxins in population regulation and the timing of the germination processes.

Formation of adducts of parthenin and related sesquiterpene lactones with cysteine and glutathione.

Parthenin, the major sesquiterpene lactone of Parthenium hysterophorus, a weed responsible for dermatitis in man is primarily restricted to leaf and stem trichomes. Parthenin forms a monoadduct with L-cysteine through the alpha-methylene group of the gamma-lactone and a biadduct with the endocyclic double bond on the cyclopentenone ring. Studies with other sesquiterpene lactones support the view that the types of adducts formed are correlated with the biological activity of the sesquiterpene lactones.

Insect feeding deterrent property of alantolactone

Abstract The sesquiterpene lactone, alantolactone, significantly reduces feeding and survival of Tribolium confusum . These findings support the view that alantolactone may protect plants such as composites from insect attack.

Visualization reagents for sesquitterpene lactones and polyacetylenes on thin-layer chromatograms

Vanillin and p-dimethylaminobenzaldehyde were found to be the most useful of several benzaldehyde and benzoic acid derivatives for the detection of sesquiterpene lactones and polyacetylenic compounds on thin-layer chromatography (TLC). Colors produced with these two reagents and with 70 sesquiterpene lactones and 25 polyacetylenes were of all shades of the spectrum and were specific for individual compounds. Therefore these reagents can be used as an aid in the identification of these compounds on TLC. These spray reagents are the most sensitive of all reagents which have so far been used for the detection of sesquiterpene lactones or polyacetylenes on TLC.

Antifungal activities of sunflower terpenoids.

Abstract Five terpenoids, two sesquiterpene lactones and three diterpene acids, isolated from cultivated sunflower, were examined for their effects on the growth of two economically important pathogens of sunflower and other crops. The minimum inhibitory concentrations of the terpenoids tested ranged from 10 to 100 ppm for Verticillium dahliae and 10 to 1000 ppm for Sclerotinium sclerotiorum. A mixture of two diterpene acids, kaurenoic and angeloylgrandifloric, was the most potent inhibitor of hyphal growth. Selective breeding to increase the amounts of these terpenoids in sunflower could improve the natural resistance in fungal pathogens.

Antifungal activity of helenin and isohelenin

Abstract Two sesquiterpene lactones, helenin and isohelenin, were examined for their activity against 16 species of fungi. These compounds varied greatly in their antifungal activities. At concentrations of 10 μg/ml, the lactones strongly inhibited the growth of Microsporum cookei, Trichophyton mentagrophytes and Trichothecium roseum , while other fungi were only inhibited by considerably higher levels (100–1000 μg/ml). It is suggested that these secondary plant metabolites might be of potential use as antifungal agents, especially if their activity and specificity could further be enhanced through modifications in their chemical structure.

Sesquiterpene lactones in various populations of Parthenium hysterophorus

Samples of 31 populations of Parthenium hyserophorus from varius areas of its world distribution were examined for their sesquiterpene lactone composition. On the basis of the occurrence of sesquiterpene lactones the samples were divided into seven chemical types. The most common is a type represented by plants containing parthenin as a major sesquiterpene lactone, and coronopilin and tetraneurin-A. All samples from North and Central America, Venezuela, South Africa, India, Australia, and one sample from Jamaica belong to this type. This suggests that P. hysterophorus recently introduced to South Africa, India and Australia originates in North and (or) Central America. On the other hand, there is a great diversity among examined South American populations. Plants from these populations usually contain hymenin which is their major sesquiterpene lactone. Some populations may also contain coronopilin, hysterin, and dihydroisoparthenin. A high diversity in the sesquiterpene lactone chemistry and the morphological differences between individual South American populations of this species indicate the possible existence of several taxa.

Inhibition of fungal growth by selected sesquiterpene lactones

Abstract Three groups of sesquiterpene lactones, each with two closely related compounds, were examined for their effects of hyphal growth of three agriculturally important fungal pathogens. The most biologically active pair was alantolactone and isoalantolactone which, at the minimum inhibitory concentration (MIC) of 1 to 5 ppm, significantly inhibited growth of four isolates of Fusarium graminearum and two of each of Verticillium albo-atrum and Leptosphaeria maculans . Growth of the eight isolates also was significantly inhibited by 1 to 5 ppm of leptocarpin but related hydroxyleptocarpin was much less active, having MIC values 10 to 50 fold higher. The MIC value for each of the third pair of sesquiterpene lactones, parthenin and coronopilin, was 1 ppm for three isolates and 100 ppm for one isolate. Growth of a highly virulent isolate of V. albo-atrum was less sensitive than a weakly virulent isolate to parthenin and coronopilin.

Effect of selected pseudoguaianolides on survival of the flour beetle, Tribolium confusum

Four pseudoguaianolides, parthenin, helinalin, coronopilin and tenulin, were tested for their effects on survival of the confused flour beetle, Tribolium confusum. Tenulin had no significant effect in concentrations tested but the other three compounds significantly reduced survival of the beetles when present in food in concentrations higher than 3.0%. It is suggested that the α-methylene-γ-lactone moiety (absent in tenulin but present in the other three lactones) is responsible for the detrimental properties of selected pseudoguaianolides on survival of flour beetles, whereas the α-β-unsaturated ketone functionality (present in tenulin, parthenin, and helenalin)does not contribute to those properties.