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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 .

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.

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.

Potential allelopathic guaianolides from cultivar sunflower leaves, var. SH-222

Abstract The leaf aqueous extracts of cultivar sunflower ( Helianthus annuus L.) var. SH-222® afforded, from the medium polar fractions, five new guaianoli

Heliannuol E. A novel bioactive sesquiterpene of the heliannane family

Abstract From the medium polar active fractions of leaf aqueous extracts of Helianthus annuus L. cv. SH-222, we have isolated heliannuol E (1) which contains a previously unknown six-membered ring containing bicyclic skeleton. The structural elucidation is based on extensive spectral studies, including 1H1H COSY, 1H13C HETCOR, and NOE difference experiments.

HELIESPIRONE A. THE FIRST MEMBER OF A NOVEL FAMILY OF BIOACTIVE SESQUITERPENES

Abstract (−)-Heliespinore A, the first member of a novel family of bioactive sesquiterpenes, a potential allelopathic agent, has been isolated from cultivar sunflower var. SH-222® (Helianthus annuus L.). The structure displays an unusual previously unknown spirosesquiterpene skeleton of Heliespirane. The structure elucidation of Heliespinone A was performed by homo- and hetero- nuclear 2D-NMR spectral data. On the basis of combined studies of the theoretical conformations and NOEDIFF data its relative stereochemistry is proposed.

Synthesis of heliannane skeletons. Facile preparation of (±)-heliannuol D☆

Heliannuol D is a natural product with a 7,10-heliannane skeleton, isolated from Helianthus annuus. It has been synthesized in eight steps, in good yield, using a new biomimetic method. Key steps were a Fries rearrangement, a Grignard reaction and, finally, a base catalyzed cyclization.