Isolated polyacetylene

The discovery of junipal focused the attention of Sorensen, who had been investigating the occurrence of polyacetylenes in Com-positae, on the possibility that these acetylenes were accompanied by thiophenes. From Coreopsis grandiflora Hogg ex sweet, 2-phenyl 5-(1-propynyl) thiophene (240) was isolated and its structure confirmed by synthesis of the tetrahydro compound, 2-phenyl-5-n-propyl-thiophene. From the root of tansy, the cis and trans isomers of methyl 5-(l-propynyl)-2-thienylacrylate (241) have been isolated. The total synthesis of trans (241) was achieved by reacting junipal with methylcarbethoxy triphenylphosphonium bromide (Wittig reaction) Several monosubstituted thiophenes, (242), (243), and... 

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. 

Polyacetylenes Beilis perennis SiOj Pentane - Et20 UV 254 nm Isolation 63 D 3"... 

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. 

Figure 13 shows the irreversible conversion of a nonconjugated poly (p-phenylene pentadienylene) to a lithiun-doped conjugated derivative which has a semiconducting level of conductivity (0.1 to 1.0 S/cm) (29). Obviously, the neutral conjugated derivative of poly (p-phenylene pentadienylene) can then be reversibly generated from the n-type doped material by electrochemical undoping or by p-type compensation. A very similar synthetic method for the conversion of poly(acetylene-co-1,3-butadiene) to polyacetylene has been reported (30), Figure 14. This synthesis of polyacetylene from a nonconjugated precursor polymer containing isolated CH2 units in an otherwise conjugated chain is to be contrasted with the early approach of Marvel et al (6) in which an all-sp3 carbon chain was employed.

Bendz, G. Marasin, an antibiotic polyacetylene, isolated from the culture... 

Mo2(0R)6 compounds in hydrocarbon solvents rapidly polymerize acetylene to a black metallic-looking form of polyacetylene. Propyne is polymerized to a yellow powder, while but-2-yne yields a gelatinous rubber-like material (45). The detailed nature of these polymers is not yet known and the only molybdenum containing compounds recovered from these polymerization reactions were the Mo2(0R)6 compounds. When the reactions were carried out in the presence of pyridine/hexane solvent mixtures, simple adducts Mo2(0R)6(py)2(ac) were isolated for R = i-Pr and CH2-t-Bu, and ac = HCCH, MeCCH and MeCCMe (45,46). 

The tendency towards explosive decomposition noted for dihalo-2,4-hexadiyne derivatives appears to be associated more with the co-existence of halo- and acetylene functions in the same molecule, than with its being a polyacetylene. Haloacetylenes should be used with exceptional precautions [1], Explosions may occur during distillation of bromoacetylenes when bath temperatures are too high, or if air is admitted to a hot vacuum-distillation residue [2], Precautions necessary in isolating and handling such compounds on the small (1 g) scale are detailed [3], Individually indexed compounds are ... 

Nakano, Y., H. Matsunaga, T. Saita, and M. Mori. 1998. Antiproliferative constituents in Umbelliferae plants II. Screening for polyacetylenes in some Umbelliferae plants, and isolation of panaxynol and falcarindiol from the root of Heracelum moellendorffii. Biol. Pharm. Bull. 21 257-261. 

The acetylene compounds - Panaxynol and falcarindiol, isolated from the roots of Saposhnikovia divaricata (Turcz.) Schischk. (Umbelliferae), selectively inhibited 5-LOX (ICso = 2 pM), leukocyte-type 12-LOX (IC50 = 1 pM), platelet-type 12-LOX (IC50 = 67 pM), and 15-LOX (IC50 = 4 pM). The same compounds had only marginal effects on COX activities with IC50 > 100 pM [126]. Bidens campylotheca Schultz Bip. ssp. campylotheca (Compositae) is a Hawaiian folk medicine for throat, stomach and asthmatic disorders. The polyacetylenes isolated from the aerial parts of the plants, such... 

Membranes for gas separation have recently attracted much attention since membrane separation is one of promising energy-saving operations 104). For example, membranes for the oxygen enrichment of air, the isolation of helium, and the removal of C02 and S02 from natural gas are being intensively studied. The high gas permeability of substituted polyacetylenes, especially of poly[l-(triinethylsilyl)-l-propyne], is described below. 

Linear polyacetylenes are found frequently in marine sponges of the order Haplosclerida (11). Although the chain lengths vary from Ci4 to C49, likely they are to be derived from Cie fatty acids. Polyacetylenes show a wide range of bioactivities, including antimicrobial, cytotoxic, antiviral, and enzyme inhibitory. Corticatic acid A (8), which is a C31 polyacetylene carboxyhc acid isolated from Petrosia corticata, is not only antimicrobial, but also it inhibits geranylgeranyltransferase I (12). 

About 85% of the known polyacetylenes were isolated from the roots and aerial parts of higher plants (up to a few grams per kilogram dry tissue). They are common... 

The first fungal polyacetylenes like mycomycin (33) and agrocybin (39) were detected and isolated on account of their antibiotic properties however, their comparative instability precluded any practical application. 

Copolymers with longer polyene segments were found to be insoluble in the reaction solvent (toluene). In these materials, the polyacetylene fraction was crystalline (97). Copolymers with a low acetylene content were composed of a variety of isolated crystalline structures within an amorphous matrix, whereas those containing 50% or more polyacetylene had a morphology that resembled fibrillar polyacetylene. Dried copolymer solutions and suspensions gave blue films with the mechanical properties characteristic of the carrier polymer. No increase in environmental stability was observed. 

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