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Accueil du site → Doctorat → États-Unis → 1978 → Chemical constituents of Encelia farinosa Gray

University of Arizona (1978)

Chemical constituents of Encelia farinosa Gray

Marshall, George Pharris

Titre : Chemical constituents of Encelia farinosa Gray

Auteur : Marshall, George Pharris

Université de soutenance : University of Arizona

Grade : Doctor of Philosophy (PhD) 1978

The desert composite Encelia farinosa Gray has been investigated and the chemical structures of the secondary metabolites therein have been determined. The steam volatile oil was analyzed by preparative GLC and was found to contain three monoterpenes and a benzofuran derivative, all of known structure. These compounds were shown to be borneol, 1,8-cineole, a-pinene, and 2-isopropenyl-6.-acetyl- 7-hydroxybenzofuran. The ethanol extract of the woody stems of-E. farinosa were found to contain three chromenes, all previ ously unreported as constituents of this plant. One of the chromenes has been reported previously on the basis of spectral evidence and was found to be 6-vinyl-7-methoxy- 2,2-dimethylbenzo-l-pyran. The remaining chromenes isolated from the plant were new compounds, 6-ethy1-7-methoxy-2,2- dimethylbenzo-l-pyran and 6-(a-methoxyethyl)-7-methoxy-2,2- dimethylbenzo-l-pyran. The latter was isolated mainly as its artifact, 6-(a-ethoxyethyl)-7-methoxy-2,2-dimethyl- benzb-l-pyran. The structures of all of these chromenes were confirmed by unambiguous synthesis from resorcinol. The exudate of E . ’farinosa was found to contain two new compounds, 2-isopropyl-6-acetyl-7-hydroxybenz ofuran and 2- [2-(6-acetyl-7-hydroxybenzofuranyl)]-4-[6-(7-methoxy-2,2- dimethylbenzo-l-pyranyl)]-pent-2-ene. These compounds were identified on the basis of spectral evidence. Also present in the exudate was the known 6-acetyl-7-methoxy-2,2- dimethylbenzo-l-pyran, whose structure was confirmed by two independent syntheses. Biosynthetic pathways are proposed for all compounds isolated from E. farinosa and their chemotaxonomic signifi cance is discussed.


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