Juan C. G. Galindo

Fungicidal activity of natural and synthetic sesquiterpene lactone analogs.

Fungicidal activity of 36 natural and synthetic sesquiterpene lactones with guaianolide, trans, trans-germacranolide, cis, cis-germacranolide, melampolide, and eudesmanolide carbon skeletons was evaluated against the phytopathogenic fungi Colletotrichum acutatum, C. fragariae, C. gloeosporioides, Fusarium oxysporum, Botrytis cinerea, and Phomopsis sp. Dose-response data for the active compounds dehydrozaluzanin C, dehydrocostuslactone, 5alpha-hydroxydehydrocostuslacone, costunolide, and zaluzanin C are presented. A new 96-well microbioassay procedure for fast and easy evaluation of antifungal activity was used to compare these compounds with commercial fungicide standards. Some structure-activity conclusions are also presented.

Potential allelopathic activity of several sesquiterpene lactone models

Abstract A collection of 12 natural and synthetic sesquiterpene lactones with eudesmanolide, melampolide, cis,cis -germacranolide, and guaianolide skeletons have been prepared and tested as allelochemicals. The effect of a series of aqueous solutions at 10 −4 -10 −9 M ofthis collection is evaluated. The specific structural requirements related to their activity is discussed. The natural sesquiterpene lactones soulangianolide A, melampomagnolide A and B, zaluzanin C and isozaluzanin C have been synthesized from costunolide, parthenolide and dehydrocostuslactone using SeO 2 and tert -butylhydroperoxide. The structures of the synthetic compounds were established by NMR spectroscopy.

Dehydrozaluzanin C, a natural sesquiterpenolide, causes rapid plasma membrane leakage

Abstract Dehydrozaluzanin C, a natural sesquiterpene lactone, is a weak plant growth inhibitor with an I50 of about 0.5 mM for lettuce root growth. It also causes rapid plasma membrane leakage in cucumber cotyledon discs. Dehydrozaluzanin C is more active at 50 μM than the same concentration of the herbicide acifluorfen. Symptoms include plasmolysis and the disruption of membrane integrity is not light dependent. Reversal of its effects on root growth was obtained with treatment by various amino acids, with histidine and glycine providing ca. 40% reversion. The strong reversal effect obtained with reduced glutathione is due to cross-reactivity with DHZ and the formation of mono- and di-adducts. Photosynthetic, respiratory and mitotic processes, as well as NADH oxidase activity appear to be unaffected by this compound. Our results indicate that dehydrozaluzanin C exerts its effects on plants through two different mechanisms, only one of which is related to the disruption of plasma membrane function.

Sunflower sesquiterpene lactone models induce Orobanche cumana seed germination.

Six sunflower sesquiterpene lactone models which share structural features of the lactone rings of strigol and its synthetic analogues, the GR family, with different conformational flexibilities were tested as Orobanche cumana germination stimulants. Among them, parthenolide and 3,5-dihydroxydehydrocostus-lactone significantly increased O. cumana germination, presenting higher activity than GR-24, used as a standard in the germination bioassay. The effect of these two compounds is species-specific, showing no germination stimulant activity on other Orobanche spp. tested (O. crenata, O. ramosa and O. aegyptiaca). Data presented are discussed in terms of a structure-activity relationship.

Dehydrozaluzanin C: a potent plant growth regulator with potential use as a natural herbicide template.

The natural product dehydrozaluzanin C (former DHZ) is a sesquiterpene lactone obtained from different weeds of the Compositae family. Its potential as a plant growth regulator has been evaluated by using a phytotoxic allelopathic bioassay, where the commercial herbicide Logran is used as internal reference. The evaluation is made based on their effects on germination and growth over several dicotyledon and monocotyledon species. The activity was tested in the range of 1000-0.001 microM. In almost all cases, DHZ was more active than the internal reference at 1000 microM, and its activity fell below the level of the internal reference at 100 microM. These results confirm DHZ as a potent plant growth regulator and a good candidate for the development of new herbicide models.

Bioactive steroids and triterpenes from Melilotus messanensis and their allelopathic potential

The aerial parts of Melilotus messanensis (sweet clover) afforded, from moderately and polar bioactive fractions, 11 triterpenes and five steroids. A series of aqueous solutions at 10−4–10−9 M of five steroids and nine triterpenes was monitored to test their effects on germination and growth of the monocots Hordeum vulgare and Allium cepa, and the dicots Lactuca sativa (var. nigra and var. romana) and Lycopersicon esculentum. An important stimulatory effect on H. vulgare germination (between 40% and 80% for almost all tested compounds) was observed. Some considerations about the ecological role of triterpenes on M. messanensis are made. In addition to known lupane triterpenes (platanic acid and 3β,28,30-lup-20(29)-enetriol), oleanane triterpenes (soyasapogenol B, soyasapogenol G, and messagenolide), a gammacerane triterpene (gammacer-16-en-3-one), five new lupane triterpenes (messagenic acids A–E: (27-cis-4-hydroxycinnamoyloxy)-betulinic acid; 27-(trans-4-hydroxycinnamoyloxy)betulinic acid; 20(S)-3β-hydroxy-29-oxolupan-28-oic acid; 3β,30-dihydroxylup-20(29)-en-28-oic acid; and 3β,20-dihydroxylup-18(19)-en-28-oic acid, respectively), and sterols (β-sitosterol, ergosterol peroxide, 7α-hydroxysitosterol, 7β-hydroxysitosterol, and 7-oxositosterol) were isolated and chemically characterized. Their structures and stereochemistry were elucidated by spectroscopic methods (one- and two-dimensional 1H and 13C NMR, IR, MS).

Allelopathic agents from aquatic ecosystems: potential biopesticides models

Allelopathy is usually regarded as a terrestrial science and little attention has been paid to the allelochemicals involved in the interactions between aquatic autotrophs. Also, chemicals involved in the interaction between algae (macro or microscopic) and their environment are not often acknowledged as allelopathic. Allelopathy is a key factor for explaining microalgae assemblages, community structure and the dynamics of the populations within the ecosystem. Herein we present an overview of what is known in this field, describing the chemicals yet identified and which kind of interactions are they involved in.

Bioactive polar triterpenoids from Melilotus messanensis

Abstract In addition to the known 3-oxoplatanic acid, melilotigenin and soyasapogenol E, two new lupane (messagenic acids F, G), two nor-lupane triterpenic acids (messagenic acids H, I), and three new oleanane triterpenes (melilotigenins B-D) were isolated and characterized from the polar bioactive fractions of Melilotus messanensis. The synthesis of messagenic acids D, F, G, betulonic acid and 3,29-dioxolup-20(30)-en-28-oic acid has been carried out from betulinic acid. These compounds exhibited clear selectivity (parameters and species) over germination and growth of monocotyledon species with average of inhibition of −50% on the germination of Hordeum vulgare, and average of stimulation of 30% on the germination of Allium cepa.

Allelochemicals fromPilocarpus goudotianus leaves.

The effect on germination, shoot, and root growth by bergapten, xanthotoxin, imperatorin, xanthyletin, xanthoxyletin, luvangetin, donatin and alloxanthoxyletol fromPilocarpus goudotianus leaves, onLactuca sativa var. nigra seedlings has been evaluated. A structure-activity correlation is discussed based on the bioassay results. Furanocoumarins appear to be the most active compounds in comparison with pyrano- and simple coumarins. The presence of an oxygenated function at C-8 decreases the germination effect in furano- and pyranocoumarins, while C-5 substituents do not cause significant changes on the activity.

New chemical clues for broomrape-sunflower host-Parasite interactions : Synthesis of guaianestrigolactones

A comparative structure-activity relationship (SAR) study has been conducted with several guaianolide sesquiterpene lactones (SLs) as inducers of the germination of sunflower broomrape (Orobanche cumana) seeds. Compounds were selected and synthesized to study the influence of the lactone-enol-gamma-lactone moiety on the selectivity of SLs toward the stimulation of sunflower broomrape germination. The results clearly illustrate that SLs are recognized only by O. cumana, while the introduction of a strigol-like second lactone moiety in the guaianolide backbone results in the loss of specificity and hence the germination of other broomrape species. We have named this new class of compounds guaianestrigolactones (GELs).