Bibenzyls structures

Evidences have confirmed that bisbibenzyls can be produced by the coupling of two phenolic systems by means of free-radical reactions. These reactions can be mediated by oxidase enzymes. C-C bonds involving positions ortho or para to the original phenols, or ether linkages, may be formed in coupling of two of these bibenzyl structures [105]. A previous hypothesis for the biogenesis of... 

The use of stronger acid conditions provides somewhat better synthetic yields of alkanes from alkynes. A useful method consists of treatment of the substrate with a combination of triethylsilane, aluminum chloride, and excess hydrogen chloride in dichloromethane.146 Thus, treatment of phenylacetylene with 5 equivalents of triethylsilane and 0.2 equivalents of aluminum chloride in this way at room temperature yields 50% of ethylbenzene after 1.5 hours. Diphenylacetylene gives a 50% yield of bibenzyl when treated with 97 equivalents of triethylsilane and 2.7 equivalents of aluminum chloride after 2.8 hours. Even 1-hexyne gives a mixture of 44% n -hexane and 7% methylpentane of undisclosed structure when treated with 10 equivalents of triethylsilane and 0.5 equivalent of aluminum chloride for 0.5 hour.146... 

The most famous of these compounds is combretastatin A-4 (CA-4,7), isolated by Pettit et al. in 1989 [30]. Pettit s research led to the isolation and structural determination of a series of phenanthrenes, dihydrophenanthrene, stilbene, and bibenzyl compounds [31]. CA-4 (7), alongside CA-1 (8), was found to be an extremely active inhibitor of tubulin polymerization [30,32]. The major problems associated with these compounds were poor bioavailability and low aqueous solubility [33,34], and hence, research in the field was turned to designing better alternatives with the hope of eradicating the negative properties of these potent compounds. 

Studies on phytotoxicity of bibenzyl derivatives were extended to duckweed axenic cultures. Bibenzyls 19 and 20 as well as the synthetic analogs 23—28 were tested by triplicate in cultures of the small aquatic plant. Analogs 23—28 were synthesized to investigate the effect on phytotoxicity of oxygenated substituents (phenolic vs. phenolic methyl ether) and their location on the bibenzyl core structure. All synthesized analogs but... 

PKSs are characterized by their ability to catalyze the formation of polyketide chains from the sequential condensation of acetate units from malonate thioesters. In plants they produce a range of natural products with varied in vivo and pharmacological properties. PKSs of particular note include acridone synthase, bibenzyl synthase, 2-pyrone synthase, and stilbene synthase (STS). STS forms resveratrol, a plant defense compound of much interest with regard to human health. STS shares high sequence identity with CHS, and is considered to have evolved from CHS more than once. ° Knowledge of the molecular structure of the CHS-like enzymes has allowed direct engineering of CHS and STS to alter their catalytic activities, including the number of condensations carried out (reviewed in Refs. 46, 51, 52). These reviews also present extensive, and superbly illustrated, discussions of CHS enzyme structure and reaction mechanism. 

Also, the peak for a benzyl trimer-d8 was almost as intense as that for bibenzyl-d4 the -d8 trimer must have the structure... 

The bibenzyls isolated in this work are closely related structurally to stilbenes and various products isolated by other workers (.10> 16, 20, 24) usually by alkali treatment of lignin or wood. Hagglund has suggested... 

Asakawa Y, Toyota M, Tori M, Hashimoto T (2000) Chemical Structures of Macrocyclic Bis(bibenzyls) Isolated from Liverworts (Hepaticae). Spectroscopy 14 149... 

By incorporation of transparent process cell, performing photochemical reactions is possible. The example shows the conversion of dibenzyl ketone to bibenzyl by irradiation of the reaction mixture with a 450 W xenon lamp. The CO produced by the reaction is vented and the bibenzyl product is purified, if desired, through a micro structured chromatographic separator unit and withdrawn off-line [84] ... 

Dormancy in yam bulbs (Dioscorea batatas) was found to be induced by three inhibitors, batatasins I, II, and III (72, 73). The structures for batatasins I and III were assigned recently. Batatasin I is 6-hydroxy-2,4,7-trimethoxyphenanthrene and batatasin III is 3,3-dihydroxy-5-methoxy-bibenzyl. Biogeneti-cally, hydrangenol, lunalaric acid and batatasin III appear to... 

The compounds were proposed to be dichloro C6-polychlorodibenzo-furans [46]. Similar observations from pulp mill samples were done by Kuehl et al. [47]. They suggested the structures of these compounds to be chlorinated xanthenes and xanthones. Buser et al. reported the occurrence of methyl-, polymethyl-, and alkyldibenzofurans in pulp mill sludge and sediments [48], Later, C5-PCBBs were detected as three dichloro and four trichloro congeners in pulp mill effluents, recipient sediment, and mussels incubated in recipient water [49]. Mass spectra of these congeners ruled out the structure of alkyl polychlorodibenzofurans and supported chlorinated alkyl bibenzyls instead, which was verified by model compound syntheses of the both structure types [50-52]. 

In the past 12 years, about 800 novel Stilbenoids have been isolated and identified. According to their structural characteristics, they are classified into six types, namely, stilbenes, bibenzyls, bisbibenzyls, phenanthrenoids, stilbene oligomers and other stilbenoids. 

The H NMR fingerprints of the CDCb extracts in small quantities of three specimens of Plagiochila exigua from Scotland are very similar and dominated by the spectrum of the new compound 3,4-dihydroxy-3 -methoxybibenzyl (128). The isolation, characterization and structural elucidation of this bibenzyl and its corresponding diacetate by means of NMR and GC/GC-MS are reported [74]. 

Fig. (8). Structures of prenylated, geranylated and famesylated bibenzyls (Group B) Table 6. Simple Bibenzyls (Group A)...

Up to now, the only bibenzyl possessing a famesyl group (180) was isolated from an unidentified Radula species and the structure established as shown in Fig. (8) [104]. 

It is evident that the three new aromatics (208—210) isolated from the New Zealand liverwort Balantiopsis rosea stem from a bibenzyl. The structure of compound 209 was established by NMR and X-ray crystallographic analysis and the absolute configurations of these structures were determined by CD analysis [104]. 

Of the bisbibenzyls research during the recent years, several highlights must be mentioned. They include the elucidation of the polychlorinated bisbibenzyls, the absolute configuration of isoplagiochins C and D (261 and 262) and structurally-related bazzanins, the first linkage found between a bibenzyl and a phenanthrene, to name a few. 

In addition to bazzanin K (280), other structures coupled between a bibenzyl and a phenanthrene are (+)-cavicularin (298) [149], shancilin (299) [109], compounds 300 and 301 [150], and phoyunnanin D (302) from Pholidota yunnanensis [5]. The linkage of the bibenzyl and phenanthrene moiety of the latter four is via an ester bond, while bazzanin K (280) is linked via two-biphenol bonds and (+)-cavicularin (298) is via one biphenol bond and an ester bond. The structure of (+)-cavicularin (298) was further confirmed by X-ray crystallographic analysis [149]. 

Three new dihydrophenanthrenes, stemanthrenes A-C (356-358), along with the above mentioned bibenzyls (133, 135, 136 and 138) were isolated and identified from the underground parts of Stemona cf. pierrei. The structures showed a common substitution pattern for aromatic ring A and characteristic C-methylations for ring B. The trivial name, racemosol, for ring B was redefined to stemanthrene D (359) due to its priority for another compound [76]. 

According to the TLC Cladosporium bioassay (bioautography), the four structural types of Stemona collinsae, stilbenes, bibenzyls,... 

The bibenzyls from the tubers of Gymnadenia conopsea, including the structure gymconopin D (181), were found to inhibit the new antigen-induced degranulation by 65.5 to 99 99% at 100 / M in RBL-2H3 cells [105]. 

Asymmetric total synthesis of terpenoids possesing novel structure of macrocyclic ethers with two bibenzyl fragments 00YGK1167. 

From the effect of solvent (Table 15) it is evident that the reactions discussed are nitrene reactions hydrogen-rich solvents suppress ring contraction and give rise to solvent dimer (bibenzyl) and/or a yellow nitrene dimer. The structure of the dimer is not known, but one possibility is shown in 144. A similar (colorless) dimer was obtained from 9-phenanthridylnitrene at 500 ° 7). Xhe two dimers formed from 137 and 141 in cyclohexane have nearly identical IR spectra. How could a hydrogen-rich solvent promote dimeriztion There is evidence from aryl azide decomposition in solution that amino radicals are formed first, and these dimerize and dehydrogenate as shown for 1-naphthylnitrene in [Eq. (48)] 82). 

It is a reasonable assumption that macrocyclic bis(bibenzyls) such as the marchantins arise by oxidative C-C or ether bond formation from acyclic precursors already containing all four aromatic rings (e.g. perrotetin E). The ether linkage between the second and third rings is probably also established by phenol oxidation. Gnetifolin, though phytochemically unrelated, is structurally rather similar to bis(bibenzyls) (Scheme 20). 

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