Date of Award

1995

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

Nikolaus H. Fischer

Abstract

Phytochemical investigations of four members of the genus Magnolia (family Magnoliaceae) were performed to provide lignans and sesquiterpene lactones. The aerial parts of the rare Louisiana native M. pyramidata afforded eight new neolignans with a novel skeleton, pyramidatin A to H. Leaves of M. virginiana provided the known sesquiterpene lactones parthenolide and costunolide as well as the new costunolactol and costunolactol dimer. An annual study of the leave constituents of M. virginiana illustrated that native M. virginiana only produces sesquiterpene lactones but transferred M. virginiana, possibly a northern variety, produces only lignans. The leaves of M. soulangiana gave five known lignans and neolignans, galgravin, veraguensin, futoenone, denudatone and denadatin A. The leaves of M. acuminata provided five burchellin-type neolignans and one new neolignan, acuminatin B. Detailed structural elucidations of all known and new compounds were performed by application of spectroscopic methods. A chemical study of roots of blue-flowered lettuce, Lactuca floridana (family Asteraceae), gave the known guaianolides 8-acetyllactucin, 8-desoxylactucin and 8-acetyl-11$\beta$H, 13- dihydrolactucin as well as the known eudesmanolides reynosin and santamarine. Biosynthetic studies of the lactucin derivatives in transformed root cultures, popularly known as hairy roots, of L. floridana were performed by application of high-field NMR techniques using $\sp{13}$C-labeled acetate and mevalonate precursors. The differentiated root cultures of L. floridana established by the stable integration of root-inducing (Ri) plasmid of the soil bacterium Agrobacterium rhizogenes into the plant genome provide a convenient source for the production of root-derived secondary metabolites at high and stable production level. Incorporation data with specifically labeled $\sp{13}$C-enriched precursors confirmed the previous biogenetic proposal that guaianolide-type sesquiterpene lactones are formed via the acetate-mevalonate-germacradiene pathway. Incorporations of $\sp{13}$C-labeled precursors into the guaianolide skeleton is highly specific and must therefore be enzymatically controlled. The biosynthetic investigations demonstrate that hairy root cultures provide a suitable medium for biosynthetic studies of sesquiterpene lactones. A biosynthetic study of root constituents of Helenium amarum using the hairy root biotechnology was attempted. However, no significant $\sp{13}$C incorporations were observed.

Pages

190

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