Kenneth L. Stevens

Allelopathic polyacetylenes fromCentaurea repens (Russian knapweed)

The allelopathic weed Russian knapweed (Centaurea repens) was found to contain polyacetylenes VIII–XIV in the roots. Dose vs. response of the root length elongation against lettuce, alfalfa, barnyard grass, and red millet showed IX to be active. Closely related isomers were not active. Examination of the soil surrounding the Russian knapweed roots revealed the presence of IX in sufficient concentration to have an appreciable effect on the surrounding plant community.

Sesquiterpene lactones from Centaurea repens

Abstract Six sesquiterpene lactones have been isolated and characterized from Centaurea repens. They are identified as cynaropicrin, repin, janerin, aguerin B, repdiolide and epoxyrepdiolide.

Transformations of geraniol in aqueous acid solutions

Abstract Geraniol decomposition in aqueous oxalic acid yields twenty-three identified products, most of which retain the oxidation level of geraniol and result from simple hydration and proton-transfer reactions. However, a large quantity of the reduced alcohol, citronellol, is formed along with cymenol, the oxidation product of α-terpineol, indicating that hydride ion transfer reactions play a major role in these terpene alcohol interconversions.

Phytotoxic properties of nordihydroguaiaretic acid, a lignan fromLarrea tridentata (Creosote bush)

The phytotoxic properties of nordihydroguaiaretic acid (NDGA) isolated from creosote bush,Larrea tridentata (Zygophyllaceae), were examined. NDGA dramatically reduces the seedling root growth of barnyard grass, green foxtail, perennial ryegrass, annual ryegrass, red millet, lambsquarter, lettuce, and alfalfa, and reduces the hypocotyl growth of lettuce and green foxtail. It has no effect on the germination of lettuce seeds. NDGA almost certainly contributes to the observed allelopathic nature of creosote bush.

Isoflavones of the heartwood of dalbergia retusa

Abstract Ether extracts of the heartwood Dalbergia retusa yield two crystalline isoflavones, identified by degradation, spectra, and synthesis as 7,8-dihydroxy-4′-methoxyisoflavone (retusin) and 7-hydroxy-8,4′-dimethoxyisoflavone (8-O-methylretusin).

Quinonoid constituents of Dalbergia retusa heartwood

Abstract Light petrol. extracts of Dalbergia retusa heartwood yield major quantities of obtusaquinone and minor amounts of the blue-black quinhydrone of racemic 4-methoxy-dalbergione.

Biogenetic-type syntheses of isoprenoid and diisoprenoid derivatives of orcinol

Abstract The products formed by condensation of orcinol with 2-methyl-3-buten-2-ol, with geraniol, and with linalool in aqueous solutions of organic acids have been separated and identified. C-isoprenyl- and C-geranyl-orcinols are obtained as major products. Minor amounts of the corresponding hydrates, chromans, chroman hydrates, and hexahydroxanthene derivatives are also formed.

Sesquiterpene lactones from Centaurea solstitialis

Abstract Eight sesquiterpene lactones were isolated from Centaurea solstitialis (yellow starthistle). They are solstitialin A, repin, subluteolide, acroptilin, janerin, cynaropicrin, and the new lactones solstitiolide and episolstitiolide.

The antimicrobial activity of citral

Bestätigung früherer Feststellungen, dass Citral eine antibakterielle Aktivität besitzt. Da Neral und Geranial (allein oder zusammen) jedoch wesentlich weniger aktiv sind, muss für die Citralaktivität eine bisher nicht identifizierte Substanz verantwortlich sein.

Acid-catalyzed and thermal rearrangements of obtusaquinol and related 3,3-diarylpropenes

Abstract Thermal rearrangement of the natural neoflavanoid, (±)-obtusaquinol, yields (±)-obtusafuran. In aqueous acid media obtusaquinol, latifolin and related phenolic 3,3-diarylpropenes rearrange to the isomeric 2-cinnamylphenols. The acid-catalyzed transformations involve initial elimination of a cinnamyl cation. 3-Cinnamylflavans are formed as minor products in these reactions.