Date of Award

1992

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

Nikolaus H. Fischer

Abstract

In a biochemical systematic study of the tribe Heliantheae, the isolation and structural elucidation of secondary metabolites from four species is reported. The aerial parts of Melampodium leucanthum afforded, besides the known melampolides melampodin A acetate, leucanthin B and leucanthinin, the new lactone leucanthinin-4-epoxide. Peracid oxidation of leucanthinin provided its monoepoxide derivative, the physical and spectroscopical data of which were identical with the new natural lactone. The isolation and structural elucidation of 7$\alpha$-hydroxydehydrocostus lactone, 13-hydroxy-11,13-dihydro-7,11-dehydro-3-desoxy-zaluzanin C and reynosin from Podachaenium eminens is reported. The isolation of the furanoheliangolides atripliciolide 2-methylbutyrate, atripliciolide tiglate and 17,18-dihydrobudlein A from Pappobolus nigrescens was accomplished. The aerial parts of Rudbeckia missouriensis afforded the diterpene acid ($-$)-kaur-16-en-19-oic acid and the corresponding aldehyde. There was no evidence of the presence of sesquiterpene lactones. The detailed structure elucidation using spectroscopical methods is described. In continuation of a study on oxidative transformations of natural sesquiterpene lactones, dehydrocostus lactone was subjected to oxidative transformations. Dehydrocostus lactone was isolated from costus resinoid, the essential oil of roots of Saussurea lappa Clark (Compositae), which is widely used as a blending agent in the perfume industry, and has been found to possess several biological activities. Oxidation with m-chloroperoxybenzoic acid afforded mono- and diepoxides. Allylic oxidation with selenium dioxide and $\sp{t}$butyl hydroperoxide afforded 3-epizaluzanin C. Singlet oxygen oxidation with methylene blue as sensitizer produced very small amount of oxidation products. The synthesis of a series of $\beta$-hydroxy-$\alpha$-methylene-$\gamma$-lactones was attempted. The synthetic approach involved the condensation of 2-acetoxycycloalkanone with ethyl-2-(phenylthio)proprionate, prepared from the reaction of ethyl-2-bromo-proprionate with thiophenol. The 2-acetoxycyclopentanone was obtained by acetylation of 2-hydroxycyclopentanone, which was prepared through an acyloin condensation reaction of diethyl glutarate. Analysis of the products from the condensation reactions provided no evidence of the formation of the desired $\beta$-acetoxy-$\alpha$-phenylthio-$\gamma$-lactone, precursor of the targeted $\beta$-hydroxy-$\alpha$-methylene-$\gamma$-lactone. The results of the reaction sequence are discussed.

Pages

220

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