Structure Elucidation and Chemistry of Plant Natural Products in Search of Bioactive Compounds.

A phytochemical study of regional members of five genera of the family Asteraceae was performed in search of bioactive natural products. The aerial parts of Garberia heterophylla, an endemic of the Florida central ridge scrub, were investigated and afforded the known guaianolide-type sesquiterpene lactone eupahakonesin, 2,6-dimethoxybenzoquinone, epifriedelinol and the novel diterpene, garberic acid. Aerial parts of Polymnia uvedalia provided three kaurane-type diterpenes, ($-$) kaur-16-en-19-oic acid, 3$\beta$-angeloyloxy-kaur-16-enic acid, 18-angeloyloxy-kaur-16-enic acid and two melampolides, enhydrin and 2$\sp\prime$, 3$\sp\prime$-dehydromelnerin A. The molecular structure of enhydrin was determined by single crystal X-ray diffraction. Verbesina virginica roots contained three eudesmane p-coumarate, 6$\beta$-p-coumaroyloxy-eudesm-4(15)-ene, 6$\beta$-p-coumaroyloxy-eudesm-4(3)-ene, 6$\beta$-p-coumaroyloxy-4$\beta$-hydroxyeudesmane and borneol p-coumarates. Extracts of roots of Coreopsis tinctoria and C. intermedia provided phenylpropane derivatives, 1$\sp\prime$-isobutyryloxyeugenol-4-isobutyrate, its 1$\sp\prime$-acetate and the phenylpropanol derivative. The flowers of C. tinctoria afforded methyl p-coumarate. Local Erigeron annus gave 3-hydroxy-4-pyrone and three Louisiana species, E. strigosus, E. vernus, and E. procumbens and one Florida species, E. quercifolius Lam provided cis,cis-matricaria ester, dihydro-cis-matricaria ester and one acetophenone derivative. Water washes of leaves of the Florida endemic Ceratiola ericoides (Empetraceae) gave the chalcone ceratiolin and its molecular structure was established by single crystal X-ray diffraction. The mechanism of photochemical allelopathic activation of ceratiolin was studied by time-dependent spectrophotometric measurements of its aqueous solution, indicating that the degradation of ceratiolin is a facile photochemical process. GC-MS analysis of the photolysis products of ceratiolin indicated hydrocinnamic acid and photorearranged cyclopentenone derivatives. In search for biologically active natural products, thirteen sesquiterpene lactones as well as five other natural products from higher plants were tested for anti-inflammatory activity against RAW 264.7 cell line. The sesquiterpene lactones parthenolide and encelin showed the highest activity and other sesquiterpene lactones exhibited significant activities with IC$\sb{50}$ values ranging from 11 $\mu$g/ml to 0.1 $\mu$g/ml