Sesquiterpene lactones

FIGURE 25.1 Amrinone exerts positive inotropic and vasodilating actions. AMP = adenosine monophosphate, AC = adenlate cyclase, PDE = phosphodiesterase, Gs = stimulatory guanine nucleotide-binding regulatory protein. 

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Toxicity of pharmaceutically important sesquiterpenic lactones andpyrrolizidine alkaloids from Astemceae sp. 99CLY320. 

Separation methods, multichromato-graphic la 56 Serine la 246,356 lb 132 Serotonin la 70,76,239,240,262,355, 380 lb 37-39,231,243,348 Serotonin metabolites lb 327 Serum lipids la 89 Serum proteins la 74 Sesquiterpene derivatives lb 239,446 Sesquiterpene esters lb 239 Sesquiterpene glucosides la 327 Sesquiterpene lactones lb 448 Sevin lb 387-389 Si 50 000, specific surface area la 91 Silica gel, caffeine-impregnated la 85 -, surface modified la 3 Silica gel 60, specific surface area la 91... 

Jorgensen et al. [84] studied how solvent effects could influence the course of Diels-Alder reactions catalyzed by copper(II)-bisoxazoline. They assumed that the use of polar solvents (generally nitroalkanes) improved the activity and selectivity of the cationic copper-Lewis acid used in the hetero Diels-Alder reaction of alkylglyoxylates with dienes (Scheme 31, reaction 1). The explanation, close to that given by Evans regarding the crucial role of the counterion, is a stabilization of the dissociated ion, leading to a more defined complex conformation. They also used this reaction for the synthesis of a precursor for highly valuable sesquiterpene lactones with an enantiomeric excess superior to 99%. 

The hetero-COSY spectrum of 7-hydroxyfrullanolide, C15H20O3, a sesquiterpene lactone, along with the H-NMR and C-NMR data are shown. Assign the C-NMR shifts to various protonated carbons based on the cross-peaks in the hetero-COSY spectrum. 

Table 2.19 Distribution of sesquiterpene lactones in Ambrosia ambrosioides (from Seaman and Mabry, 1979b)...

The sesquiterpene lactone chemistry was reinvestigated in greater detail by Porter and Mabry (1972), who used plant material from 20 populations of A. psilostachya... 

Gershenzon, J. and Mabry, T. J. 1984. Sesquiterpene lactones from a Texas population of Helianthus maximiliaiti. Phytochemistry 23 1959-1966. 

Sesquiterpene lactones from the genus Ambrosia. Phytochemistry 10 2241-2244. 

Seaman, F. C. 1982. Sesquiterpene lactones as taxonomic characters in the Asteraceae. The Botanical Review 48 121-592. 

Sesquiterpene Lactones and Allelochemicals from Centaurea Species... 

Composites -have been reported (8) to contain a wide variety of sesquiterpene lactones and lactones of this type have been previously found in both Russian knapweed and yellow starthistle (9,10,11,12). The wide range of biological activity associated with sesquiterpene lactones, e.g., cytotoxicity, phytotoxicity, antineoplasticity, etc. (8) suggested the possibility that these compounds may play a role in the allelopathy of both Russian knapweed and yellow starthistle. 

In addition to the sesquiterpene lactones, two chromenes, Eupa-toriochromene (I) and Encecalin (II) (14) have been isolated from yellow starthistle and have been shown to have some effects on germination and growth of lettuce. 

Isolation of Sesquiterpene Lactones. The ether extract was evaporated and dissolved in 952 ethanol. Then an equal volume of 42 aqueous lead acetate was added. After 1 hour the mixture was filtered to remove precipitated chlorophyll and phenolic products and the ethanol removed under vacuum. The aqueous layer was extracted with chloroform giving a dark colored oil from which the sesquiterpenes were isolated by a combination of chromatographic procedures, i.e., LH-20 gel permeation, silica gel using both packed columns and thin layer plates. A variety of solvents were also used to purify the individual sesquiterpene lactones, e.g., benzene-acetone (1 1), ethyl acetate, chloroform-methanol (9 1). On thin layer chromatographic plates, spots were visualized by spraying with 22 aqueous KMn04 solution. 

STEVENS AND MERRILL Centaurea Sesquiterpene Lactones and Allelochemicals 85... 

STEVENS and Merrill Centaurea Sesquiterpene Lactones and AUelochemicals 97... 

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