- Easy Access to Alkoxy, Amino, Carbamoyl, Hydroxy, and Thiol Derivatives of Sesquiterpene Lactones and Evaluation of Their Bioactivity on Parasitic Weeds
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It has been hypothesized that the α-methylene-?-lactone moiety of sesquiterpene lactones is a key unit for their bioactivity. As a consequence, modifications of these compounds have been focused on this fragment. In the work reported here, two sesquiterpene lactones, namely, dehydrocostuslactone and β-cyclocostunolide, a eudesmanolide obtained by controlled cyclization of costunolide, were chosen for modification by Michael addition at C-13. On applying this reaction to both compounds, it was possible to introduce the functional groups alkoxy, amino, carbamoyl, hydroxy, and thiol to give products in good to high yields, depending on the base and solvent employed. In particular, the introduction of a thiol group at C-13 in both compounds was achieved with outstanding yields (>90%) and this is unprecedented for these sesquiterpene lactones. The bioactivities of the products were evaluated on etiolated wheat coleoptile elongation and germination of seeds of parasitic weeds, with significant activity observed on Orobanche cumana and Phelipanche ramosa. The structure-activity relationships are discussed.
- Cala, Antonio,Zorrilla, Jesús G.,Rial, Carlos,Molinillo, José M. G.,Varela, Rosa M.,Macías, Francisco A.
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- New chemical clues for broomrape-sunflower host - Parasite interactions: Synthesis of guaianestrigolactones
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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 s
- Macias, Francisco A.,Garcia-Diaz, Maria D.,Perez-De-Luque, Alejandro,Rubiales, Diego,Galindo, Juan C.G.
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- Synthesis of Active Strigolactone Analogues Based on Eudesmane- And Guaiane-Type Sesquiterpene Lactones
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Strigolactones are natural products that are exuded by plants and stimulate parasitic weed germination. Their use in herbicides is limited since they are produced in small quantities, but the synthesis of bioactive analogues provides an alternative source. In this work, eleven analogues have been synthesized. Among them, nine compounds belong to a novel family named eudesmanestrigolactones. The procedure is short (3-6 steps), the starting materials are isolated on a multigram scale, and global yields are up to 8%, which significantly enhance isolated yields. In bioassay, the compounds germinated high percentages of Phelipanche ramosa, Orobanche cumana, and Orobanche crenata seeds, even at nanogram doses (100 nM). Bioactivity was stereochemistry-dependent, and it was discussed in terms of the presence and geometry of the enol ether, orientation of the butenolide, and unsaturation of ring A. The reported compounds provide a set of readily obtained allelochemicals with potential applications as preventive herbicides.
- Cala, Antonio,Macías, Francisco A.,Molinillo, José M. G.,R. Mejías, Francisco J.,Rial, Carlos,Varela, Rosa M.,Zorrilla, Jesús G.
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p. 9636 - 9645
(2020/10/18)
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- Sesquiterpene lactones with potential use as natural herbicide models. 2. Guaianolides
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A structure-activity study to evaluate the effect of 17 guaianolide sesquiterpene lactones (in a range of 100-0.001 μM) on the growth and germination of several mono- and dicotyledon target species is accomplished. Results are compared with those obtained in the same bioassay with an internal standard, the commercial herbicide Logran, to validate the results with a known active formulation and to compare the results with a commercial product to test their potential use as natural herbicide models. Specific conditions for the selective mono- or polyhydroxylation of guaianolides using the SeO2/tert-butyl hydroperoxide system are presented and discussed. The high regio- and stereo-selectivities of the reaction are explained through the specific structural requirements of the bulky first adduct formed during the ene reaction. These compounds appear to have deeper effects on the growth of either monocots or dicots than the previously tested germacranolides. Otherwise, the lactone group seems to be necessary for the activity, though it does not necessarily need to be unsaturated. However, the presence of a second and easily accessible unsaturated carbonyl system greatly enhances the inhibitory activity. Lipophilicity and the stereochemistry of the possible anchoring sites are also crucial factors for the activity. Finally, the levels of growth inhibition obtained with some compounds on dicots or monocots are totally comparable to those of Logran and allow proposing them as lead compounds.
- Macias, Francisco A.,Galindo, Juan C. G.,Castellano, Diego,Velasco, Raul F.
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p. 5288 - 5296
(2007/10/03)
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- Fungicidal activity of natural and synthetic sesquiterpene lactone analogs
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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, 5α-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. (C) 2000 Elsevier Science Ltd.
- Wedge,Galindo,Macias
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p. 747 - 757
(2007/10/03)
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