Francisco A. Macías

Just how insoluble are monoterpenes

Prior generalizations about the ecological roles of monoterpenes may be misleading if based on the presumed insolubility of monoterpenes in water. We determined the aqueous solubility of 31 biologically active monoterpenes by gas chromatography. While hydrocarbons were of low solubility (< 35 ppm), oxygenated monoterpenes exhibited solubilities one or two orders of magnitude higher, with ranges of 155–6990 ppm for ketones and of 183–1360 ppm for alcohols. Many monoterpenes are phytotoxic in concentrations under 100 ppm, well below the saturated aqueous concentrations of oxygenated monoterpenes. Therefore, even dilute, unsaturated solutions of monoterpenes, occurring naturally in plant tissues and soil solutions, may act as potent biological inhibitors.

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.

Bioactive norsesquiterpenes from Helianthus annuus with potential allelopathic activity

Abstract Six bioactive norsesquiterpenes have been isolated from Helianthus annus (sunflower) var. SH-222® and VYP®. Three new ionone type bisnorsesquiterpenes and a new norbisabolene are potential allelopathic agents. Their structures were determined through the analysis of their homo- and hetero-nuclear 2D-NMR spectral data. On the basis of combined studies of the theoretical conformations and NOEDIFF data the relative stereochemistry is proposed. These compounds exhibited clear selectivity (parameters and species) with monocotyledon species with an average of inhibition of −45% on the germination of Allium cepa and an average of stimulation of 50% on the root growth of A. Cepa and Hordeum vulgare in a range of concentrations of 10 −5 –10 −9 .

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.

Bioactive terpenoids from sunflower leaves cv. Peredovick.

The CH(2)Cl(2) extract of dried leaves of Helianthus annuus L. cv. Peredovick(R) has yielded, in addition to the known sesquiterpene lactones annuolide E and leptocarpin, and the sesquiterpenes heliannuols A, C, D, F, G, H, I, the new bisnorsesquiterpene, annuionone E, and the new sesquiterpenes heliannuol L, helibisabonol A and helibisabonol B. Structural elucidation was based on extensive spectral (one and two-dimensional NMR experiments) and theoretical studies. The sesquiterpenes heliannuol A and helibisabonol A and the sesquiterpene lactone leptocarpin inhibited the growth of etiolated wheat coleoptiles.

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.

Novel sesquiterpene from bioactive fractions of cultivar sunflowers.

Abstract From the medium polar active fractions, we have isolated a sesquiterpene heliannoul A. It contains a previously unknown skeleton, heliannuol, whose str

Potential allelopathic sesquiterpene lactones from sunflower leaves

Abstract Isolation, structure elucidation and allelopathic bioassays of 13 sesquiterpene lactones, four of them new, from the sunflower cultivar VYP ® are described. Structures of the lactone assigned as 1,2-anhydrido-4,5-dihydroniveusin A, previously isolated from capitate glandular trichomes of Helianthus annuus and of annuithrin are corrected. The effect of a series of aqueous solutions at 10 −4 –10 −9 M of the sesquiterpene lactones was studied on the root and shoot lengths of Lactuca sativa var. nigra, Lepidium sativum, Lycopersicon esculentum , seedlings (dicotyledons) and Hordeum vulgare and Triticum estivum (monocotyledons). The guaianolides generally had no effect on the germination and growth of L. sativum and L. esculentum , except for C-10 epimers 8β-angeloyloxycumambranolide and annoulide G where inhibitory effects were found on the shoot length of L. esculentum . Both exhibit similar activity profiles, the most persistenty active compound on dilution was 8β-angeloyloxycumambranolide with an α-orientated hydroxyl group at C-10. The conformational changes due to functionalization within germacranolides influence principally root and shoot growth. Heliangolides have greater effect on root and shoot length of dicotyledon species, presumably due to conformational flexibility and the presence of electrophylic groups.

Allelochemicals from sunflower leaves cv. Peredovick

Abstract Isolation, structural elucidation and allelopathic bioassays of 13 compounds, isolated from sunflower cultivar cv. Peredovick are described. Two new sesquiterpene lactones, helivypolide D and helivypolide E and the bisnorsesquiterpene, annuionone D, which is reported at the first time as natural product, are described. The effects of a series of aqueous solutions at 10−4–10−9 M of these compounds were studied on the root and shoot lengths of Lactuca sativa, Lepidium sativum seedlings (dicotyledons) and Hordeum vulgare and Allium cepa (monocotyledons).

Bioactive flavonoids from Helianthus annuus cultivars

Abstract Isolation, structure elucidation and allelopathic bioassay of five flavonoids (the flavonol tambulin, the chalcones kukulcanin B and heliannone A, and the flavanones heliannones B and C) from the sunflower cultivar VYP® are described. Heliannones A–C are reported in the literature as natural products, for the first time. The effects of a series of aqueous solutions at 10−4–10−9 M of the flavonoids on the root and shoot length of Lycopersicon esculentum and Hordeum vulgare has been studied. They influence, principally, the shoot growth of seedlings, but germination and radical length can be affected by chalcones. The effects of very similar compounds, kukulcanin B and heliannone A, varied. The reason for this variation could be related to the number and position of free hydroxy groups.