- Iron-catalyzed arene C-H hydroxylation
-
The sustainable, undirected, and selective catalytic hydroxylation of arenes remains an ongoing research challenge because of the relative inertness of aryl carbon-hydrogen bonds, the higher reactivity of the phenolic products leading to over-oxidized by-products, and the frequently insufficient regioselectivity. We report that iron coordinated by a bioinspired L-cystine-derived ligand can catalyze undirected arene carbon-hydrogen hydroxylation with hydrogen peroxide as the terminal oxidant. The reaction is distinguished by its broad substrate scope, excellent selectivity, and good yields, and it showcases compatibility with oxidation-sensitive functional groups, such as alcohols, polyphenols, aldehydes, and even a boronic acid. This method is well suited for the synthesis of polyphenols through multiple carbon-hydrogen hydroxylations, as well as the late-stage functionalization of natural products and drug molecules.
- Cheng, Lu,Wang, Huihui,Cai, Hengrui,Zhang, Jie,Gong, Xu,Han, Wei
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- Oxygen-Free Regioselective Biocatalytic Demethylation of Methyl-phenyl Ethers via Methyltransfer Employing Veratrol- O-demethylase
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The cleavage of aryl methyl ethers is a common reaction in chemistry requiring rather harsh conditions; consequently, it is prone to undesired reactions and lacks regioselectivity. Nevertheless, O-demethylation of aryl methyl ethers is a tool to valorize natural and pharmaceutical compounds by deprotecting reactive hydroxyl moieties. Various oxidative enzymes are known to catalyze this reaction at the expense of molecular oxygen, which may lead in the case of phenols/catechols to undesired side reactions (e.g., oxidation, polymerization). Here an oxygen-independent demethylation via methyl transfer is presented employing a cobalamin-dependent veratrol-O-demethylase (vdmB). The biocatalytic demethylation transforms a variety of aryl methyl ethers with two functional methoxy moieties either in 1,2-position or in 1,3-position. Biocatalytic reactions enabled, for instance, the regioselective monodemethylation of substituted 3,4-dimethoxy phenol as well as the monodemethylation of 1,3,5-trimethoxybenzene. The methyltransferase vdmB was also successfully applied for the regioselective demethylation of natural compounds such as papaverine and rac-yatein. The approach presented here represents an alternative to chemical and enzymatic demethylation concepts and allows performing regioselective demethylation in the absence of oxygen under mild conditions, representing a valuable extension of the synthetic repertoire to modify pharmaceuticals and diversify natural products.
- Grimm, Christopher,Lazzarotto, Mattia,Pompei, Simona,Schichler, Johanna,Richter, Nina,Farnberger, Judith E.,Fuchs, Michael,Kroutil, Wolfgang
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p. 10375 - 10380
(2020/10/02)
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- Structural features and antioxidant activities of Chinese quince (Chaenomeles sinensis) fruits lignin during auto-catalyzed ethanol organosolv pretreatment
-
Chinese quince fruits (Chaenomeles sinensis) have an abundance of lignins with antioxidant activities. To facilitate the utilization of Chinese quince fruits, lignin was isolated from it by auto-catalyzed ethanol organosolv pretreatment. The effects of three processing conditions (temperature, time, and ethanol concentration) on yield, structural features and antioxidant activities of the auto-catalyzed ethanol organosolv lignin samples were assessed individually. Results showed the pretreatment temperature was the most significant factor; it affected the molecular weight, S/G ratio, number of β-O-4′ linkages, thermal stability, and antioxidant activities of lignin samples. According to the GPC analyses, the molecular weight of lignin samples had a negative correlation with pretreatment temperature. 2D-HSQC NMR and Py-GC/MS results revealed that the S/G ratios of lignin samples increased with temperature, while total phenolic hydroxyl content of lignin samples decreased. The structural characterization clearly indicated that the various pretreatment conditions affected the structures of organosolv lignin, which further resulted in differences in the antioxidant activities of the lignin samples. These results can be helpful for controlling and optimizing delignification during auto-catalyzed ethanol organosolv pretreatment, and they provide theoretical support for the potential applications of Chinese quince fruits lignin as a natural antioxidant in the food industry.
- Cheng, Xi-Chuang,Guo, Xin-Ran,Liu, Hua-Min,Liu, Yu-Lan,Qin, Zhao,Wang, Xue-De
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p. 4348 - 4358
(2020/09/22)
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- Biocatalytic Methyl Ether Cleavage: Characterization of the Corrinoid-Dependent Methyl Transfer System from Desulfitobacterium hafniense
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The ether functionality represents a very common motif in organic chemistry and especially the methyl ether is commonly found in natural products. Its formation and cleavage can be achieved via countless chemical procedures. Nevertheless, since in particular the cleavage often involves harsh reaction conditions, milder alternatives are highly demanded. Very recently, we have reported on a biocatalytic shuttle catalysis concept for reversible cleavage and formation of phenolic O-methyl ethers employing a corrinoid-dependent methyl transferase system from the anaerobic organism Desulfitobacterium hafniense. Here we report the technical study of this system, focusing on the demethylation of guaiacol as model reaction. The optimal buffer-, pH-, temperature- and cofactor-preferences were determined as well as the influence of organic co-solvents. Beside methyl cobalamin also hydroxocobalamin turned out to be a suitable cofactor species, although the latter required activation. Various O-methyl phenyl ethers were successfully demethylated with conversions up to 82% at 10 mM substrate concentration. (Figure presented.).
- Richter, Nina,Farnberger, Judith E.,Pompei, Simona,Grimm, Christopher,Skibar, Wolfgang,Zepeck, Ferdinand,Kroutil, Wolfgang
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p. 2688 - 2695
(2019/03/28)
-
- Cleavage of Catechol Monoalkyl Ethers by Aluminum Triiodide-Dimethyl Sulfoxide
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Using eugenol and vanillin as model substrates, a practical method is developed for the cleavage o -hydroxyphenyl alkyl ethers. Aluminum oxide iodide (O=AlI), generated in situ from aluminum triiodide and dimethyl sulfoxide, is the reactive ether cleaving species. The method is applicable to catechol monoalkyl ethers as well as normal phenyl alkyl ethers for the removal of methyl, ethyl, isopropyl, and benzyl groups. A variety of functional groups such as alkenyl, allyl, amide, cyano, formyl, keto, nitro, and halogen are well tolerated under the optimum conditions. Partial hydrodebromination was observed during the demethylation of 4-bromoguaiacol, and was resolved using excess DMSO as an acid scavenger. This convenient and efficient procedure would be a practical tool for the preparation of catechols.
- Sang, Dayong,Tian, Juan,Tu, Xiaodong,He, Zhoujun,Yao, Ming
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p. 704 - 712
(2019/01/23)
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- Synthesis and antichlamydial activity of novel phenazines
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Background: Chlamydiae are widespread Gram-negative bacteria that cause a number of human diseases. Chlamydia trachomatis is the most prevalent sexually transmitted bacterial pathogen. Methods: Fourteen novel phenazine derivatives were efficiently synthesized via Buchwald-Hartwig cross coupling reaction and Suzuki reaction from 4-bromo-1-methoxyphenazine. All the derivatives displayed antichlamydial activity with IC50 values from 1.01-19.77 μM against Chlamydia trachomatis D and L2 for inhibiting progeny formation. Results: C-4 morpholinyl 8a and C-4 phenyl phenazine 9c exhibited stronger antichlamydial activity with no apparent cytotoxicity. Both phenazine derivatives inhibited chlamydial inclusions formation and growth in a dose-dependent manner. They inhibited Chlamydia infection by reducing elementary body infectivity and disturbing Chlamydia growth at the mid-stage of the chlamydial developmental cycle. Conclusion: Our findings suggest C-4 aryl and C-4 amino phenazine derivatives as promising lead molecules for antichlamydials development.
- Bao, Xiaofeng,Yu, Xiaowei,Xia, Chao,Yang, Ningjing,Yang, Shengju,Zhao, Yu
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p. 174 - 181
(2019/01/04)
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- Ether bond cracking method of phenylalkyl ether
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The invention discloses an ether bond cracking method of phenylalkyl ether. The method comprises the following steps: performing ether bond breaking reaction on phenylalkyl ether at -20 to reflux temperature in the presence of aluminium triiodide and dimethyl sulfoxide, thereby generating phenol and derivatives thereof. The method disclosed by the invention is mild in condition, simple and convenient for operation, high in yield, and extensive in applicable phenylalkyl ether range.
- -
-
Paragraph 0181-0183
(2018/11/26)
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- Enzyme-Catalysed Synthesis of Cyclohex-2-en-1-one cis-Diols from Substituted Phenols, Anilines and Derived 4-Hydroxycyclohex-2-en-1-ones
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Toluene dioxygenase-catalysed cis-dihydroxylations of substituted aniline and phenol substrates, with a Pseudomonas putida UV4 mutant strain and an Escherichia coli pCL-4t recombinant strain, yielded identical arene cis-dihydrodiols, which were isolated as the preferred cyclohex-2-en-1-one cis-diol tautomers. These cis-diol metabolites were predicted by preliminary molecular docking studies, of anilines and phenols, at the active site of toluene dioxygenase. Further biotransformations of cyclohex-2-en-1-one cis-diol and hydroquinone metabolites, using Pseudomonas putida UV4 whole cells, were found to yield 4-hydroxycyclohex-2-en-1-ones as a new type of phenol bioproduct. Multistep pathways, involving ene reductase- and carbonyl reductase-catalysed reactions, were proposed to account for the production of 4-hydroxycyclohex-2-en-1-one metabolites. Evidence for the phenol hydrate tautomers of 4-hydroxycyclohex-2-en-1-one metabolites was shown by formation of the corresponding trimethylsilyl ether derivatives. (Figure presented.).
- Boyd, Derek R.,Sharma, Narain D.,McIntyre, Peter B. A.,Stevenson, Paul J.,McRoberts, W. Colin,Gohil, Amit,Hoering, Patrick,Allen, Christopher C. R.
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p. 4002 - 4014
(2017/11/22)
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- Synthesis of α-oxygenated ketones and substituted catechols via the rearrangement of N-enoxy- and N-aryloxyphthalimides
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A common approach to the synthesis of α-oxygenated carbonyl compounds and catechols is the treatment of a carbonyl compound or a phenol with an electrophilic oxygen source. As an alternative approach to these important structures, formal [3,3]-rearrangements of N-enoxyphthalimides, N-enoxyisoindolinones, and N-aryloxyphthalimides have been explored. When used in combination with an initial Chan-Lam coupling, these transformations facilitate the dioxygenation of alkenylboronic acids for the synthesis of α-oxygenated ketones and the dioxygenation of arylboronic acids for the synthesis of catechols. The rearrangements of N-enoxyisoindolinones have also been shown to be diastereoselective.
- Kroc, Michelle A.,Patil, Aditi,Carlos, Anthony,Ballantine, Josiah,Aguilar, Stephanie,Mo, Dong-Liang,Wang, Heng-Yen,Mueller, Daniel S.,Wink, Donald J.,Anderson, Laura L.
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p. 4125 - 4137
(2017/06/29)
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- H2O2 in WEB: a highly efficient catalyst system for the Dakin reaction
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Without using any transition metal catalyst, ligand, base, toxic or hazardous reagent, additives/promoters and organic solvent, green Dakin reactions have been successfully carried out by using H2O2 in a natural feedstock extract. The reaction proceeds in neat 'Water Extract of Banana' (WEB) at room temperature under aerobic conditions in very short reaction times and, therefore, it is an evergreen and environmentally sound alternative to the existing protocols for the Dakin reaction. In our system, the reaction was found to afford excellent yield for the desired product with different electron-withdrawing and electron-donating hydroxylated benzaldehydes.
- Saikia, Bishwajit,Borah, Parinita,Barua, Nabin Chandra
-
supporting information
p. 4533 - 4536
(2015/09/15)
-
- A new avenue to the Dakin reaction in H2O2-WERSA
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We have developed a novel protocol to realize the Dakin reaction in a more greener way. In fact, by the use of H2O2-WERSA, we can oxidize aromatic arylaldehydes to phenols at room temperature. It is remarkable that the catalytic system does not require activation or any toxic ligand, additive/promoter, transition metal catalyst, base, organic solvent and so on. A range of substituted hydroxylated benzaldehydes were screened to investigate the scope of this protocol.
- Saikia, Bishwajit,Borah, Parinita
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p. 105583 - 105586
(2015/12/30)
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- N-protected 1,2-oxazetidines as a source of electrophilic oxygen: Straightforward access to benzomorpholines and related heterocycles by using a reactive tether
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A hitherto unknown reactivity of a strained four-membered heterocycle, 1,2-oxazetidine, is reported. When reacted with organometallic compounds, this reagent provides electrophilic oxygen with a nitrogen-terminated two-carbon-atom tether. The synthetic versatility of the products obtained was demonstrated in various transformations, leading to efficient synthesis of six-, seven-, and eight-membered heterocyclic systems of pharmaceutical importance. Open and then close: The O-selective ring-opening reaction of 1,2-oxazetidines with organometallic compounds provides tethered phenol derivatives that can be used to access six-, seven-, and eight-membered heterocyclic systems in only a few steps (see scheme; Ts=tosyl).
- Javorskis, Tomas,Sriubaite, Simona,Bagd?iunas, Gintautas,Orentas, Edvinas
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supporting information
p. 9157 - 9164
(2015/06/16)
-
- Toluene dioxygenase-catalyzed synthesis and reactions of cis -diol metabolites derived from 2- and 3-methoxyphenols
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Using toluene dioxygenase as biocatalyst, enantiopure cis-dihydrodiol and cis-tetrahydrodiol metabolites, isolated as their ketone tautomers, were obtained from meta and ortho methoxyphenols. Although these isomeric phenol substrates are structurally similar, the major bioproducts from each of these biotransformations were found at different oxidation levels. The relatively stable cyclohexenone cis-diol metabolite from meta methoxyphenol was isolated, while the corresponding metabolite from ortho methoxyphenol was rapidly bioreduced to a cyclohexanone cis-diol. The chemistry of the 3-methoxycyclohexenone cis-diol product was investigated and elimination, aromatization, hydrogenation, regioselective O-exchange, Stork-Danheiser transposition and O-methylation reactions were observed. An offshoot of this technology provided a two-step chemoenzymatic synthesis, from meta methoxyphenol, of a recently reported chiral fungal metabolite; this synthesis also established the previously unassigned absolute configuration.
- Boyd, Derek R.,Sharma, Narain D.,Malone, John F.,McIntyre, Peter B. A.,McRoberts, Colin,Floyd, Stewart,Allen, Christopher C. R.,Gohil, Amit,Coles, Simon J.,Horton, Peter N.,Stevenson, Paul J.
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p. 3429 - 3439
(2015/04/14)
-
- Multidimensional optimization of promising antitumor xanthone derivatives
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A promising antitumor xanthone derivative was optimized following a multidimensional approach that involved the synthesis of 17 analogues, the study of their lipophilicity and solubility, and the evaluation of their growth inhibitory activity on four human tumor cell lines. A new synthetic route for the hit xanthone derivative was also developed and applied for the synthesis of its analogues. Among the used cell lines, the HL-60 showed to be in general more sensitive to the compounds tested, with the most potent compound having a GI50 of 5.1 μM, lower than the hit compound. Lipophilicity was evaluated by the partition coefficient (Kp) of a solute between buffer and two membrane models, namely liposomes and micelles. The compounds showed a log Kp between 3 and 5 and the two membrane models showed a good correlation (r2 = 0.916) between each other. Studies concerning relationship between solubility and structure were developed for the hit compound and 5 of its analogues.
- Azevedo, Carlos M.G.,Afonso, Carlos M.M.,Sousa, Diana,Lima, Raquel T.,Helena Vasconcelos,Pedro, Madalena,Barbosa, Jo?o,Corrêa, Arlene G.,Reis, Salette,Pinto, Madalena M.M.
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p. 2941 - 2959
(2013/07/05)
-
- An efficient strategy for protecting dihydroxyl groups of catechols
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A novel strategy for protecting dihydroxyl groups of catechols has been developed. Base-mediated cyclizations of catechols with 1,3-dibromopropane provided the corresponding benzo[b]1,4-dioxepans, and herefrom the protecting group was easily cleaved by aluminum chloride. The preparation of the antibacterial and antifungal agent 4-(2-aminothiazol-4-yl)benzene-1,2-diol from catechol reliably verified its availability amenable to various harsh reaction conditions. Georg Thieme Verlag Stuttgart - New York.
- Huang, Wei-Bin,Guo, Ying,Jiang, Jian-An,Pan, Xian-Dao,Liao, Dao-Hua,Ji, Ya-Fei
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supporting information
p. 741 - 746
(2013/05/09)
-
- Organocatalytic Dakin oxidation by nucleophilic flavin catalysts
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Flavin catalysts perform the first organocatalytic Dakin oxidation of electron-rich arylaldehydes to phenols under mild, basic conditions. Catechols are readily prepared, and the oxidation of 2-hydroxyacetophenone was achieved. Aerobic oxidation is displayed in the presence of Zn(0) as a reducing agent. This reactivity broadens the scope of biomimetic flavin catalysis in the realm of nucleophilic oxidations, providing a framework for mechanistic investigations for related oxidations, such as the Baeyer-Villiger oxidation and Weitz-Scheffer epoxidation.
- Chen, Shuai,Hossain, Mohammad S.,Foss, Frank W.
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supporting information; experimental part
p. 2806 - 2809
(2012/08/07)
-
- Aerobic organocatalytic oxidation of aryl aldehydes: Flavin catalyst turnover by Hantzsch's ester
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The first Dakin oxidation fueled by molecular oxygen as the terminal oxidant is reported. Flavin and NAD(P)H coenzymes, from natural enzymatic redox systems, inspired the use of flavin organocatalysts and a Hantzsch ester to perform transition-metal-free, aerobic oxidations. Catechols and electron-rich phenols are achieved with as low as a 0.1 mol % catalyst loading, 1 equiv of Hantzsch ester, and O2 or air as the stoichiometric oxidant source.
- Chen, Shuai,Foss, Frank W.
-
supporting information
p. 5150 - 5153,4
(2020/09/15)
-
- Structure, stereochemistry and synthesis of enantiopure cyclohexenone cis-diol bacterial metabolites derived from phenols
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Biotransformation of 3-substituted and 2,5-disubstituted phenols, using whole cells of P. putida UV4, yielded cyclohexenone cis-diols as single enantiomers; their structures and absolute configurations have been determined by NMR and ECD spectroscopy, X-ray crystallography, and stereochemical correlation involving a four step chemoenzymatic synthesis from the corresponding cis-dihydrodiol metabolites. An active site model has been proposed, to account for the formation of enantiopure cyclohexenone cis-diols with opposite absolute configurations.
- Boyd, Derek R.,Sharma, Narain D.,Malone, John F.,McIntyre, Peter B. A.,Stevenson, Paul J.,Allen, Christopher C. R.,Kwit, Marcin,Gawronski, Jacek
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scheme or table
p. 6217 - 6229
(2012/09/05)
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- Layer-by-Layer coated tyrosinase: An efficient and selective synthesis of catechols
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Agaricus bisporous tyrosinase was immobilized on commercial available epoxy-resin EupergitC250L and then coated by the Layer-by-Layer method (LbL). The two novel heterogeneous biocatalysts were characterized for their morphology, pH and storage stability, kinetic properties (Km, V max, Vmax/Km) and reusability. These biocatalysts were used for the efficient and selective synthesis of bioactive catechols under mild and environmental friendly experimental conditions. Ascorbic acid was added in the reaction medium to inhibit the formation of ortho-quinones, thus avoiding the known enzyme suicide inactivation process. Catechols were obtained mostly in quantitative yields and conversion of substrate. Tyrosinase immobilized on EupergitC250L and coated by the LbL method showed better catalytic activities, higher pH and storage stability, and reusability with respect to immobilized uncoated tyrosinase. Since chemical procedures to synthesize catechols are often expensive and with high environmental impact, the use of immobilized tyrosinase represents an efficient alternative for the preparation of this family of bioactive compounds.
- Guazzaroni, Melissa,Crestini, Claudia,Saladino, Raffaele
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experimental part
p. 157 - 166
(2012/02/13)
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- Lignin solubilization and aqueous phase reforming for the production of aromatic chemicals and hydrogen
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The solubilization and aqueous phase reforming of lignin, including kraft, soda, and alcell lignin along with sugarcane bagasse, at low temperatures (T≤498 K) and pressures (P≤29 bar) is reported for the first time for the production of aromatic chemicals and hydrogen. Analysis of lignin model compounds and the distribution of products obtained during the lignin aqueous phase reforming revealed that lignin was depolymerized through disruption of the abundant β-O-4 linkages and, to a lesser extent, the 5-5' carbon-carbon linkages to form monomeric aromatic compounds. The alkyl chains contained on these monomeric compounds were readily reformed to produce hydrogen and simple aromatic platform chemicals, particularly guaiacol and syringol, with the distribution of each depending on the lignin source. The methoxy groups present on the aromatic rings were subject to hydrolysis to form methanol, which was also readily reformed to produce hydrogen and carbon dioxide. The composition of the isolated yields of monomeric aromatic compounds and overall lignin conversion based on these isolated yields varied from 10-15% depending on the lignin sample, with the balance consisting of gaseous products and residual solid material. Furthermore, we introduce the use of a high-pressure autoclave with optical windows and an autoclave with ATR-IR sentinel for on-line in situ spectroscopic monitoring of biomass conversion processes, which provides direct insight into, for example, the solubilization process and aqueous phase reforming reaction of lignin.
- Zakzeski, Joseph,Weckhuysen, Bert M.
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experimental part
p. 369 - 378
(2012/03/11)
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- Anodic oxidation of catechols in the presence of α-oxoketene N,N-acetals with a tetrahydropyrimidine ring: Selective α-arylation reaction
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The electrochemical oxidation of catechols leads to the formation of o-benzoquinones. This property has been applied to effectively synthesize α-arylated products of α-oxoketene N,N-acetals with a tetrahydropyrimidine ring.
- Zeng, Cheng-Chu,Ping, Da-Wei,Hu, Li-Ming,Song, Xiu-Qing,Zhong, Ru-Gang
-
scheme or table
p. 2465 - 2472
(2010/07/06)
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- Total synthesis of six natural products of benzodioxane neolignans
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(±)-Eusiderin E, (±)-Eusiderin F, (±)-Eusiderin K, (±)-Eusiderin J, (±)-Eusiderin M and (±)-Eusiderin G were first synthesized from pyrogallol, in which the Claisen Rearrangement was used to afford two important C6-C3 units.
- Jing, Xiao-Bi,Wang, Li,Han, Ying,Shi, Yao-Cheng,Liu, Yong-Hong,Sun, Jing
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p. 1001 - 1004
(2007/10/03)
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- One step hair coloring compositions using salts
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A hair coloring composition comprising the following two compositions which are mixed just prior to application to the hair: (a) a composition comprising a water-soluble peroxygen oxidizing agent; and (b) a composition comprising one or more oxidative hair coloring agents selected from the group consisting of an aromatic diamine, an amino phenol, a naphthol, a polyhydric phenol, a catechol and mixtures thereof; wherein the composition comprising one or more oxidative hair coloring agents further comprises al least one water soluble carbonate releasing salts; and optionally a water soluble ammonium salt, is described.
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- Transition metal complexes as dye forming catalysts in hair coloring compositions
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A hair coloring composition comprising a first composition which comprises: (a) a dye forming transition metal salt or complex; which is first applied to the hair; and a second composition which comprises the following two compositions which are mixed just prior to application to the hair: (a) a composition comprising a water-soluble peroxygen oxidizing agent; and (b) a composition comprising one or more oxidative hair coloring agents selected from the group consisting of an aromatic diamine, an aminophenol, a polyhydric phenol a catechol and mixtures thereof.
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- Enhanced color deposition for hair with sequestering agents
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Hair coloring compositions which comprise: (A) non-nitrogenous chelating agents from the group consisting of polyphosphate; phosphonates; hydroxycarboxylates; polyacrylates; zeolite; and mixtures thereof; (B) an oxidative dye primary intermediate; and (C) an oxidative dye coupler; (D) and water are described. The present invention also relates to a method for coloring hair which comprises contacting said hair with a hair coloring composition as described above.
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- Medium-scale preparation of useful metabolites of aromatic compounds via whole-cell fermentation with recombinant organisms
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The whole-cell fermentation of aromatic coumpounds with Escherichia coli JM109 (pDTG601) on a medium scale (10-15L) produces enantiopure cyclohexadienediols. A detailed procedure for the fermentation is described, and yields for several metabolites are provided. A similar procedure using E. coli JM109 (pDTG602) affords catechols. The dienediols are useful for asymmetric synthesis, and several important targets originating from these metabolites are tabulated.
- Endoma, Mary Ann,Bui, Vu P.,Hansen, Jeff,Hudlicky, Tomas
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p. 525 - 532
(2013/09/06)
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- Total synthesis of (±)-Eusiderin G and (±)-Eusiderin M
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(±)-Eusiderin G and (±)-Eusiderin M were first synthesized from pyrogallol, in which the Claisen Rearrangement was used to afford two important C6-C3 units.
- Jing, Xiaobi,Gu, Wenxin,Ren, Xinfeng,Bie, Pingyan,Pan, Xinfu
-
-
- Total synthesis of (±)-Eusiderin K and (±)-Eusiderin J
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(±)-Eusiderin K and (±)-Eusiderin J were first synthesized from pyrogallol, in which the Claisen Rearrangement was used to afford two important C6-C3 units.
- Jing, Xiaobi,Gu, Wenxin,Bie, Pingyan,Ren, Xinfeng,Pan, Xinfu
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p. 861 - 867
(2007/10/03)
-
- Flash vacuum pyrolysis of methoxy-substituted lignin model compounds
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The flash vacuum pyrolysis (FVP) of methoxy-substituted fi-O-4 lignin model compounds has been studied at 500 °C to provide mechanistic insight into the primary reaction pathways that occur under conditions of fast pyrolysis. FVP of PhCH2CH2OPh (PPE), a model of the dominant β-O-4 linkage in lignin, proceeds by C-O and C-C cleavage, in a 37:1 ratio, to produce styrene plus phenol as the dominant products and minor amounts of toluene, bibenzyl, and benzaldehyde. From the deuterium isotope effect in the FVP of PhCD2CH2OPh, it was shown that C-O cleavage occurs by homolysis and by 1,2- elimination in a ratio of 1.4:1, respectively. Methoxy substituents enhance the homolysis of the β-O-4 linkage, relative to PPE, in o-CH3O- C6H4OCH2CH2Ph (o-CH3O-PPE) and (o-CH3O)2-C6H3OCH2CH2Ph ((o- CH3O)2-PPE) by a factor of 7.4 and 21, respectively. The methoxy- substituted phenoxy radicals undergo a complex series of reactions, which are dominated by 1,5-, 1,6-, and 1,4-intramolecular hydrogen abstraction, rearrangement, and α-scission reactions. In the FVP of o-CH3O-PPE, the dominant product, salicylaldehyde, forms from the methoxyphenoxy radical by a 1,5-hydrogen shift to form 2-hydroxyphenoxymethyl radical, 1,2-phenyl shift, and β-scission of a hydrogen atom. The 2-hydroxyphenoxymethyl radical can also cleave to form formaldehyde and phenol in which the ratio of 1,2-phenyl shift to β-scission is ca. 4:1. In the FVP of o-CH3O-PPE and (o-CH3O)2- PPE, products (ca. 20 mol %) are also formed by C-O homolysis of the methoxy group. The resulting phenoxy radicals undergo 1,5- and 1,6-hydrogen shifts in a ratio of ca. 2:1 to the aliphatic or benzylic carbon, respectively, of the phenethyl chain. In the FVP of (o-CH3O)2-PPE, o-cresol was the dominant product. It was formed by decomposition of 2-hydroxy-3- hydroxymethylbenzaldehyde and 2-hydroxybenzyl alcohol, which are formed from a complex series of reactions from the 2,6-dimethoxyphenoxy radical. The key step in this reaction sequence was the rapid 1,5-hydrogen shift from 2- hydroxy-3-methoxybenzyloxy radical to 2-hydroxymethyl-6-methoxyphenoxy radical before β-scission of a hydrogen atom to give the substituted benzaldehyde. The 2-hydroxybenzyl alcohols rapidly decompose under the reaction conditions to o-benzoquinone methide and pick up hydrogen from the reactor walls to form o-cresol.
- Britt, Phillip F.,Buchanan III,Cooney, Mark J.,Martineau, Dan R.
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p. 1376 - 1389
(2007/10/03)
-
- Fine particulate matter (PM) and organic speciation of fireplace emissions
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This paper presents a summary of fireplace particle size and organic speciation data gathered to date in an ongoing project. Tests are being conducted in a residential wood combustion (RWC) laboratory on three factory- built fireplaces. RWC wood smoke particles 10 μm (PM10) consist primarily of a mixture of organic compounds that have condensed into droplets; therefore, the size distribution and total mass are influenced by temperature of the sample during its collection. During the series 1 tests (15 tests), the dilution tunnel used to cool and dilute the stack gases gave an average mixed gas temperature of 47.3 °C and an average dilution ratio of 4.3. Averages for the PM2.5 (particles 2.5 μm) and PM10 fractions were 74 and 84%, respectively. For the series 2 tests, the dilution tunnel was modified, reducing the average mixed gas temperatures to 33.8 °C and increasing the average dilution ratio to 11.0 in tests completed to date. PM2.5 and PM10 fractions were 83 and 91%, respectively. Since typical winter time mixed gas temperatures would usually be less than 10 °C, these size fraction results (even from the series 2 tests) probably represent the lower bound; the PM10 and PM2.5 size fractions might be higher at typical winter temperatures. The particles collected on the first stage (cutpoint ? 11.7 μm) were light gray and appeared to include inorganic ash. Particles collected on the remainder of the stages were black and appeared to be condensed organics because there was noticeable lateral bleeding of the collected materials into the filter substrate. Total particulate emission rates ranged from 10.3 to 58.4 g/h; corresponding emission factors ranged from 3.3 to 14.9 g/kg of dry wood burned. A wide range of Environmental Protection Agency (EPA) Method 8270 semivolatile organic compounds were found in the emissions; of the 17 target compounds quantified, major constituents are phenol, 2-methylphenol, 4- methylphenol, 2,4-dimethylphenol, and naphthalene. An account is given on fireplace particle size and organic speciation data gathered to date in an ongoing project. Total particulate matter emission rates and the results of analyses for semivolatile organics in the emissions are discussed.
- Purvis, Carol R.,Mccrillis, Robert C.,Kariher, Peter H.
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p. 1653 - 1658
(2007/10/03)
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- The first direct transformation of 2,2'-dihydroxychalcones into coumestans
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Three coumestans, flemichapparin, medicagol and sophoracoumestan B, are synthesised by direct reaction of the analogous 2,2'-dihydroxychalcones with thallium (III) nitrate in methanol.
- Kamara, B. Irene,Brandt, E. Vincent,Ferreira, Daneel
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p. 861 - 868
(2007/10/03)
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- Baeyer-Villiger oxidation of β-aryl substituted unsaturated carbonyl compounds with hydrogen peroxide and catalytic selenium dioxide
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A simple and cheap oxidative procedure using 30% H2O2 and catalytic SeO2 allows to transform 2-aralkylidenecycloalkanones and hydroxy- or alkoxybenzaldehydes to give, in high yields, enollactones and arylformates, respectively.
- Guzman,Mendoza,Garcia,Garibay,Oliveras,Maldonado
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p. 2121 - 2133
(2007/10/02)
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- Enzymatically amplified voltammetric sensor for microliter sample volumes of salicylate
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A new voltammetric sensing strategy for salicylate employing two enzymes and applicable to microliter sample volumes is demonstrated. The method involves the use of the enzyme salicylate hydroxylase to convert salicylate to catechol, which is oxidized at a carbon electrode. The product of this oxidation reaction, o-quinone, is then reduced by a second enzyme, glucose oxidase, to regenerate catechol. Reoxidation of catechol results in a signal that is amplified due to repeated cycling of catechol molecules between the oxidized and reduced states. This chemistry is implemented in two configurations. (i) A paper disk into which both enzymes have been absorbed is mounted on a coplanar three-electrode assembly for aqueous experiments. Determination of salicylate in a nonprescription dermatological product is demonstrated. (ii) A small solution volume confined directly on the coplanar electrodes is used for determination of salicylate in whole blood. The advantages of the use of two enzymes and of monitoring steady-state catalytic currents are discussed.
- Moore, Thea J.,Joseph, Melissa J.,Allen, Barry W.,Coury Jr., Louis A.
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p. 1896 - 1902
(2007/10/02)
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- Sodium Percarbonate: A Convenient Reagent for the Dakin Reaction
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Sodium percarbonate, a readily available, inexpensive and easy to handle reagent efficiently oxidizes hydroxylated benzaldehydes and hydroxylated acetophenones to hydroxyphenols.
- Kabalka, G. W.,Reddy, N. K.,Narayana, C.
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p. 865 - 866
(2007/10/02)
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- PREPARATION OF 2-METHOXY-3,4-METHYLENEDIOXYBENZALDEHYDE (CROWEACIN ALDEHYDE) FROM PYROGALLOL
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2-Methoxy-3,4-methylenedioxybenzaldehyde (croweacin aldehyde) of high purity was prepared in 55percent overall yield from pyrogallol.
- Shirasaka, Tadashi,Takuma, Yuki,Imaki, Naoshi
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p. 1213 - 1221
(2007/10/02)
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- Direct Lithiation of Alkoxyphenols: Metalation vs Demethylation. An Experimental and Theoretical (MNDO) Study
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The direct lithiation of simple alkoxyphenols has been studied both from a theoretical and an experimental viewpoint.Efficient lithiations were achieved by using a 2:1 tBuLi-tBuOLi mixture (LICLIOR) in THF at room temperature.In most cases alkoxy groups are responsible for the regioselectivity observed, although for the case of 2-methoxyphenol both the OMe and OLi groups actually act as ortho-directing groups during lithiation.Demethylation has been shown to be a common side reaction of lithiation of phenolic or nonphenolic alkoxy aromatics.MNDO calculations provide good support for all the experimental observations.Thus, lithiation and demethylation are shown to be competing pathways, the former being kinetically favored whereas the latter leads to the thermodynamically more stable compounds.Calculations also show that the so-called geminal demethylations are more favored processes than the alternative vicinal demethylations.Moreover, MNDO allows the measurement of the extent of agostic activation of the ortho hydrogens with respect to the OMe and OLi groups involved in lithiation.Finally, MNDO nicely predicts the important role of reaction temperature in successful direct lithiation of simple alkoxyphenols.
- Morey, Jeroni,Costa, Antoni,Deya, Pere M.,Suner, Guillem,Saa, Jose M.
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p. 3902 - 3909
(2007/10/02)
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- Synthesis of Cotarnin Iodide
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Starting from 4-methoxy-1,3-benzodioxol-5-carbaldehyde (croweacin aldehyde, 3) a six-step synthesis of cotarnin iodide (9, 67percent total yield) is described. - Keywords.Croweacinaldehyde; Isoquinoline; Cotarnin iodide.
- Fleischhacker, Wilhelm,Richter, Bernd,Urban, Ernst
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p. 765 - 770
(2007/10/02)
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- Dealkylation of Activated Alkyl Aryl Ethers Using Lithium Chloride in Dimethylformamide
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Alkyl aryl ethers having electron-withdrawing substituents in the ortho or para positions are esily cleaved with lithium chloride in dimethylformamide.
- Bernard, Angela M.,Ghiani, M. Rossella,Piras, Pier Paolo,Rivoldini, Antonio
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p. 287 - 289
(2007/10/02)
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- Boron Trichloride as a Selective Demethylating Agent for Hindered Ethers: a Synthesis of the Phytoalexins α- and β-Pyrufuran, a Synthesis of Tri-O-methylleprolomin and its Demethylation
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Boron trichloride has been found to be an efficient reagent for the selective cleavage of sterically hindered methoxy groups in methoxyarenes.The scope and utility of this reaction are explored with examples drawn from derivatives of benzene, naphtalene, 9,10-dihydrophenanthrene and dibenzofuran.The method is applied to the synthesis of the phytoalexins α- (56) and β-pyrofuran (58) (1,3,4-trimethoxydibenzofuran-2-ol and 1,2,4-trimethoxydibenzofuran-3-ol).A synthesis of tri-O-methylleprolomin (61), a derivative of the unusual lichen metabolite leprolomin (60), is described and its demethylation with boron trichloride is studied.
- Carvalho, Christopher F.,Russo, Albert V.,Sargent, Melvyn V.
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p. 777 - 792
(2007/10/02)
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- Mechanism of the Oxidation of NADH by Quinones. Energetics of One-Electron and Hydride Routes
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The kinetics of NADH oxidation by 7 o-benzoquinones and 14 p-benzoquinones were studied by using buffered aqueous solutions and UV/vis spectroscopy.For each quinone the rate law was first order in NADH and first order in quinone.The rate constants varied from 0.0745 to 9220 M-1s-1.Variation of the pH from 6 to 8 gave no change in rate.The use of 4-D and 4,4-D2NADH revealed kinetic isotope effects.The dideutero data gave kH/kD in the range 1.6-3.1 for p-quinones and 4.2 for 3,5-di-tert-butyl-o-quinone.When p-quinones were used, the log k was a linear function of Eo for the quinone/hydroquinone monoanion (Q/QH(1-)) couple with a slope of 16.9 V-1. o-Quinones reacted about 100 times more rapidly, but the same linear relationship with a slope of 16.4 V-1 was observed.Comparisons to data for one-electron-transfer reactions indicate that such mechanisms are not involved.A hydride-transfer mechanism accommodates all the data, and rate-limiting hydrogen atom transfer followed by electron transfer cannot be ruled out.
- Carlson, Brian W.,Miller, Larry L.
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p. 479 - 485
(2007/10/02)
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- Boron Trichloride as a Selective Demethylating Agent for Hindered Ethers
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Boron trichloride has been found to be an efficient reagent for the selective cleavage of sterically hindered methoxy groups in methoxyarenes; the scope and utility of this reaction are explored.
- Carvalho, Christopher F.,Sargent, Melvyn V.
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p. 227 - 229
(2007/10/02)
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- SYNTHESE TOTALES DE LA (+/-) ISO β-PELTATINE ET DE SES ANALOGUES
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α-Hydroxyalkylation of a β-(2-alkoxy 3,4-methylenedioxy benzyl)-γ-butyrolactone (17 or 25) with 3,4,5-trimethoxybenzaldehyde or syringaldehyde 27, followed by cyclisation, afforded good yields of the corresponding (+/-) isopeltatins.
- Brown, Eric,Loriot, Michel,Robin, Jean-Pierre
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p. 949 - 952
(2007/10/02)
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- The Constituents of Schizandra chinensis BAILL. IX. The Cleavage of the Methylenedioxyl Moiety with Lead Tetraacetate in Benzene, and the Structure of Angeloylgomisin Q
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A procedure for selective cleavage of the methylenedioxyl moiety with lead tetraacetate in dry benzene is described.Piperonylic acid methyl ester (5), 4-nitro-1,2-methylenedioxybenzene (6), 3,4-methylenedioxytoluene (7), 2,3-methylenedioxyanisole (8) and gomisin A (9) afforded protocatechuic acid (12), 4-nitrocatechol (13), 3,4-dihydroxytoluene(14), 2,3-dihydroxyanisole (15) and compound 16, respectively.The structure of angeloylgomisin Q isolated from the fruits of Schizandra chinensis BAILL. (Schizandraceae), was elucidated as 1 by using the above reaction.Keywords--cleavage of methylenedioxyl moiety; lead tetraacetate; Schizandra chinensis BAILL.; Schizandraceae; dibenzocyclooctadiene; lignan; angeloylgomisin Q
- Ikeya, Yukinobu,Taguchi, Heihachiro,Yoshioka, Itiro
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p. 2893 - 2898
(2007/10/02)
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- Long-chain Phenols. Part 18. Conversion of Anacardic Acid into Urushiol
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(15:0)-Anacardic acid (6-pentadecylsalicylic acid), prepared by reduction of unsaturated anacardic acid from Anacardium occidentale, has been converted into anacardic alcohol (6-pentadecylsalicylic alcohol) and thence by oxidation at carbon into anacardaldehyde.Phenolic oxidation of anacardic alcohol led to 8-pentadecyl-1-oxaspiroocta-5,7-dien-4-one, itself readily convertible photochemically, but less so thermally, into anacardaldehyde.Reaction of thionyl chloride with anacardic acid led mainly to the anhydride, which by hydride reduction gave anacardaldehyde less satisfactorily.Dakin oxidation of anacardaldehyde furnished (15:0)-urushiol (3-pentadecylcatechol) identical chemically and from argentation t.l.c. with the hydrogenated natural product from Rhus vernicifera. (15:0)-Cardanol (3-pentadecylphenol) has been detected in hydrogenated urushiol.The composition of the unsaturated constituents of urushiol from Rhus vernicifera and Rhus toxicodendron and its mode of formation have been discussed.An improved synthesis of (15:0)-urushiol has been devised based on an organo-lithium route.Aromatic methyl ether and ester formation in this series is greatly facilitated by phase-transfer catalysis.
- Kiong, Lam Soot,Tyman, John H. P.
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p. 1942 - 1952
(2007/10/02)
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- Hair dyeing composition containing an aryldiamine and a substituted catechol
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A composition for use in the dyeing of keratinous fibre such as hair includes an aqueous anaerobic solution of an aryldiamine and a substituted catechol. Optionally, an aromatic coupling agent can also be incorporated in the composition to modify the shade of color produced. Anaerobic storage conditions can, for example, be maintained by packing the composition in an aerosol container with a halocarbon propellant.
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- Reactions of Lithium Aluminium Hydride in Hydrocarbon Solvents. Selective Demethylation of Some Substituted Methyl Phenyl Ethers
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Lithium aluminium hydride in benzene or heptane is an effective reagent for selective demthylation of methyl phenyl ethers having additional ether functions in the immediate vicinity of the reaction site.
- Carrol, John F.,Kulkowit, Sunanta,McKervey, M. Anthony
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p. 507 - 508
(2007/10/02)
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