Date of Award

1991

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

Nikolaus H. Fischer

Abstract

The major chemical constituents of Magnolia acuminata, M. ashei, M. cordata, M. dealbata, M. fraseri, M. freemani, M. little gem, M. macrophylla, M. tripetala and M. virginiana were studied as part of a continuing search for biologically active secondary metabolites from regional plant sources and the investigation of their biosynthesis and large scale production. All these Magnolia species are rich in fatty acids and several also contain monoterpenes, sesquiterpenes, sesquiterpene lactones and lignans. The organic extract of the leaves of Magnolia virginiana provided a new sesquiterpene lactone, 4,14-dehydromagnograndiolide, and the new sesquiterpene lactol costunolactol. The known sesquiterpene lactones parthenolide and costunolide, as well as several sesquiterpene hydrocarbons, were also identified. Dried leaves of Magnolia freemanii afforded the sesquiterpene lactones parthenolide, peroxyparthenolide, michelenolide, dihydrosantamarine and reynosin. The latter two are probably formed by cyclization of the related costunolide-1,10-epoxides during chromatographic separation on silica gel. The major components of the organic extract of the leaves of Magnolia tripetala were in order: the known lignan magnolol, its isomer honokiol, the mono-methyl ether of honokiol, and its acetyl derivative. Total assignment of the $\sp{13}$C NMR signals of thiarubrine A, $\beta$-trans-bergamotene, 7-isobutyryloxythymol isobutyrate, and 7-isobutyryloxy-8,9-dehydro epoxythymol isobutyrate was obtained using modern NMR techniques which included INAPT, COSY, HETCOR, Gated Decoupling and DEPT. Spectra of $\sp{13}$C-enriched thiarubrine A, obtained from hairy root cultures of Ambrosia artemisiifolia by incorporation of (1-$\sp{13}$C) -, (2-$\sp{13}$C) - and (1,2-$\sp{13}$C$\sb2$) -acetate, showed patterns of enrichment consistent with a biosynthetic pathway in which the thirteen-carbon 1,2-dithiin arises from a longer-chain precursor, most likely a fourteen-carbon homolog, by carbon-carbon scission. Likewise, the spectra of $\sp{13}$C-enriched $\beta$-bisabolene and $\beta$-trans-bergamotene, derived by incorporation of (1-$\sp{13}$C) -, (2-$\sp{13}$C) - and (1,2-$\sp{13}$C$\sb2$) -acetate in A. artemisiifolia root cultures, showed patterns of enrichment consistent with the hypothesis that the biosynthesis of sesquiterpenes proceed via the mevalonic acid pathway. Biosynthetic studies of 7-isobutyryloxythymol isobutyrate and 7-isobutyryloxy-8,9-dehydroepoxythymol isobutyrate, as well as an acetylenic sulfone were attempted in hairy root cultures of Gaillardia pulchella, using (1-$\sp{13}$C) -, (2-$\sp{13}$C) - and (1,2-$\sp{13}$C) -labeled sodium acetate as precursors; however, $\sp{13}$C incorporations were too low, and no conclusions concerning probable biosynthetic pathways were possible.

Pages

132

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