Natural polyacetylenic products

These methods have also been applied to the development of a novel route to conjugated diynes, directed toward natural polyacetylenic products. Substituted... 

An interesting example of regioselective CM with ethylene as a tool in natural product degradation was recently disclosed by Hawaiian authors [149]. Thus, CM using catalyst C and ethylene gas was used to degrade the plant polyacetylene oxylipin (+)-falcarindiol (342) with uncertain stereochemistry at C3. As the reaction provided a meso product (343) in 81% yield by regioselective attack at the aliphatic side chain, the natural compound 342, isolated from a Hawaiian endemic plant, had the 3R,8S configuration shown in Scheme 66. 

Propiolaldehyde diethyl acetal has found numerous synthetic applications in the literature which may be briefly summarized. The compound has been utilized in the synthesis of unsaturated and polyunsaturated acetals and aldehydes by alkylation of metal-lated derivatives, " by Cadiot-Chodkiewicz coupling with halo acetylenes, " and by reaction with organocuprates. Syntheses of heterocyclic compounds including pyrazoles, isoxazoles, triazoles, and pyrimidines have employed this three-carbon building block. Propiolaldehyde diethyl acetal has also been put to use in the synthesis of such natural products as polyacetylenes " and steroids. ... 

In a search for allelopathic agents from common weeds, Amaranthus palmerl S. Wats (Palmer amaranth) and Ambrosia artemisiifolia L. (Louisiana annual ragweed) have been analysed for their organic natural products. From A. palmerl phytol, chondrlllasterol, vanillin, 3-methoxy-4-hydroxynitrobenzene and 2,6-dimethoxy- benzoquinone were isolated. From the roots of Ambrosia artemisiifolia four polyacetylenes, a mixture of sesquiterpene hydrocarbons, methyl caffeate, and a mixture of 8-sitosterol and stlgmasterol were obtained. 

The genus Artemisia contains more than 200 species that have been reported from many parts of the world and has been selected for remedies by cultures throughout the world because of its medicinal properties. The reported active constituents of the genus include all types of the common natural products of the Asteraceae SQLs, polyacetylenes, flavonoids, essential oils (monoterpenes),... 

Wang, N., Yao, X., Ishii, R., and Kitanaka, S. Antiallergic agents from natural sources. 3. Structures and inhibitory effects on nitric oxide production and histamine release of five novel polyacetylene glucosides from Bidens parviflora Willd. Chem Pharm Bull (Tokyo), 49(8), 938-942, 2001. 

The product contains (besides some residual F and H) also inserted NBU4 , i.e. it is naturally n-doped. Even in the absence of BuOH, reactive nucleophiles like [(CH3)2NCHO] or (CH3)2N can be generated by preelectrolysis of dimethylformamide solutions [59]. Such a process allows electrochemical deposition of diamond-like carbon on an aluminum electrode [78] and it also produces polyyne from PVDF (cf. Eq. 4.22a). At similar conditions, PTFE shows no reactivity [59] and polyvinylchloride is dehydrohalogenated only to polyacetylene [79-82]. However, Zra 5-poly-acetylene, which was stereoregularly chlorinated by FeCh, is carbonizable by electrochemically generated BuO (cf. reactions 4.22 and 4.22a) [83] ... 

A detailed interpretation of LC/ H-NMR in combination with LC/UV-DAD, LC/MS, and chemotax-onomical data (see the case of 3 in Figure 5) enables the identification of three known lignanes ( —)-phylligenin (3), ( —)-eudesmin (4), ( —)-epieudesmin (5) as well as polycerasoidol (6). Compound (7) could be completely identified based on online data and was finally characterized as a new polyacetylenic natural product named oropheic acid (7). This example also demonstrates the use of LC/UV LC/MS and LC/NMR in phytochemical analysis known natural products can be dereplicated by comparison... 

Flores, H. E., J. J. Pickard, and M. W. Hoy, Production of polyacetylenes and thiophenes in heterotrophic and photosynthetic root cultures of Asteraceae, in Naturally Occurring Acetylenes and Related Compounds (J. Lam, H. Breteler, T. Amason, and L. Hansen, eds.), 233-254, Elsevier, Amsterdam, 1988. 

Although a great deal of research has been done on the finished product, polyacetylene film or powder, very little is known about the nature of the catalyst. This led us to carry out an extensive spectroscopic investigation with the object of finding out more about the structure of the active sites, both from measurements on newley prepared, aimealed and aged catalysts as well as on the catalyst during polymerization of (CH)jf. 

The synthesis of enynes is of interest in the chemistry of certain natural products. Terminal enynes occur in several natural products such as histrionicotoxin and laurencin, and the internal enyne unit is found along with polyacetylenes and allenes in natural products from Compositae and Umbelliferae. Both internal Z-and. E-enynes are also useful as precursors to stereochemically define d dienes on their partial reduction. A group from Phillips-Duphar has described an efficient synthesis of the functionalized enyne (95), which serves as the C5 synthon for the convergent synthesis of vitamin A. The l,3-dichloro-2-ether (94) is dechlorinated, substituted, and isomerized in one step on reaction with two molar equivalents of sodium acetylide in liquid ammonia, giving (95) with an E Z ratio... 

The formulation of any biosynthetic pathway depends on the isolation or at least on the detection of all the presumed intermediates. Polyacetylenic compounds are often unstable molecules whose successful isolation depends on the techniques used in handling both the plants and their extracts. The possible influence of work-up procedures on the yields of isolated components has been recently investigated with thin-layer chromatography over silica gel, a standard analytical and preparative procedure in natural products analysis. The recovery of 1 and a-terthienyl (Tl) placed on silica gel plates ranged between 77% and 97%... 

Yet, compared to the other x-systems, the acyclic linear polyenes, and the cyclic oligoenes (i.e., the annulenes), cross-conjugated molecules have lived in the shadows so far. Acyclic linear polyenes are encountered widely in fatty acid, polyketide, and terpenoid natural product domains and the ultimate polyene, polyacetylene is a conductive polymer that was the focus of the 2000 Chemistry Nobel Prize. The annulenes played crucial roles in the development of practical and theoretical organic chemistry (aromatic and antiaromatic compounds), and serve as pivotal bulk chemicals in industry (benzene, toluene, the xylenes, styrene, etc.). 

De novo fatty acid synthesis (FAS) supplies fatty acids for a large variety of lipids, including membrane lipids, epiticular waxes and cutin, neutrcd storage lipids, and many natural products, such as acyl salicylates, polyacetylenes or macrocyclic lactones. Many of these specific lipids are found in highly differentiated plant cells, where they can often represent a major part of cell dry weight. The regulation of FAS, which in most cases supplies the same fatty acids (palmitic eind oleic acids) for different end products, is therefore a key question. 

Sorensen, N. A. Structural patterns of polyacetylenic compounds isolated from the plant family Compositae, p. 569- In I. U. P. A. C. Symposium on the Chemistry of Natural Products, Australia i960. London Butterworth Co. 1961. 

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