O-methylation in vitro of dihydroxy- and trihydroxy-phenolic compounds by liver slices
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1. Historical Aspects and Industrial Syntheses of Monohydric and Dihydric Phenols. References. 2. Recent Advances in the Synthesis of Monohydric Phenols. References. 3. Reactions of the Hydroxyl Group in Monohydric Phenols. References. 4. Phenolic Ethers of Hydroxy Aromatics. References. 5. Oxidation of Phenols. References. 6. Alkyl and Hindered Phenols. References. 7. Carbonyl Derivatives of Phenols. References. 8. Halogeno, Nitro, Amino, Azo, Sulpho and Thio Derivatives of Phenols. References. 9. Dihydric Phenols. References. 10. Polyhydric Phenols. References. 11. Branched Alkylphenols of Industrial Interest. References. 12. Prenylphenols. References. 13. Non-Isoprenoid Alkylphenols. References. 14. Synthesis of Natural Phenols (and their Derivatives) of Pharmaceutical, Medicinal or Technical Interest. References. Subject Index.
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Methylation and demethylation of the methyl-accepting chemotaxis protein (MCP) was studied in vitro. The in vitro MCP methylating system showed the following characteristics. 1. Multiple bands of methylated MCP were produced. 2. The reaction could be separated into two phases: the initial phase, in which the level of methylation increased as a result of multiple methylation; and the stationary phase, in which methylation and demethylation took place at the same velocity without apparent change in the level of methylation. 3. Pulse-chase analysis of the reaction showed that MCP was demethylated preferentially at the relatively highly methylated state. 4. The behavior of MCP in this system was similar to that of MCP stimulated in vivo with attractant. Based on the above results, an autonomous control mechanism of the level of MCP methylation is discussed.
Demethylation
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This chapter contains sections titled: Introduction Structural Chemistry of Mono- and Polyhydroxybenzenes Structural Chemistry of Substituted Phenols (2–13) Substituted 1,2-Dihydroxybenzene (3) Substituted 1,3-Dihydroxybenzene (4) Substituted 1,4-Dihydroxybenzene (5) Substituted 1,3,5-Trihydroxybenzene (6) Substituted 1,2,3-Trihydroxybenzene (7) Substituted 1,2,4-Trihydroxybenzene (8) Steric and Electronic Effects on the Structural Chemistry of Phenols ortho-substituted Phenols (39) meta-substituted Phenols (40) para-substituted Phenols (41) Special Substituted Phenols Nitrophenols Fluoro, Chloro and Bromo Phenols References
Structural chemistry
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Changes occurring in the concentrations of alpha-tocopherol, total phenols, and complex phenols linked to 3,4-dihydroxyphenylethanol (fractions FII and FIV) and p-hydroxyphenylethanol (FIII) during storage of virgin olive oil under environmental conditions were studied. Under diffused light, alpha-tocopherol was decomposed by 79% in 4 months, whereas <45% of the phenols were lost during the same period. Among the phenols, FII showed the least stability, and decreased by 72% in 6 months. Total phenols, FIII, and FIV recorded reductions in the range of 57-63% in 6 months. When the oil was stored in the dark, alpha-tocopherol, total phenols, FIII, and FIV exhibited similar profiles of degradation, reducing by 39-45% in the first 6 months and 50-62% in 12 months. FII was the least stable compound in the dark and recorded a loss of 64% in 6 months and 79% in 12 months. The levels of the above antioxidants were further related to peroxide formation. Remaining levels of these compounds at PV = 20 meq/kg ranged between 50 and 73% under diffused light and between 40 and 62% in the dark.
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alpha-Tocopherol
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According to the monitoring data,which gained from four years of fild sampling and investigation in Hohhot,the characteristics of uptaking and accumulation phenols by the vegetables from polluted environment and the situations of remove and distribution of phenols in the organs of the vegtables are studied.The vegetables which are fond of (or very caplable for) or resistant to (or less capble for ) uptaking phenols are selected out and also some particular organs of some vegetables which are very capable for accumulation phenols are poited out.Based on the ratio of the contants of phenols in the vegetables and the soils,the ability of concentrition of phenols from the environment by vegetables are discussed.
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Substituted phenols are requisite molecules for human health, agriculture, and diverse synthetic materials. We report a chemical synthesis of phenols, including penta-substituted phenols, that accommodates programmable substitution at any position. This method uses a one-step conversion of readily available hydroxypyrone and nitroalkene starting materials to give phenols with complete regiochemical control and in high chemical yield. Additionally, the phenols can be converted into highly and even fully substituted benzenes.
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Ethers are the most widely used protective groups for phenols, and in general, they are more easily cleaved than the analogous ethers of simple alcohols. Esters are also important protective groups for phenols, but are not as stable to hydrolysis as the related alcohol derivatives. Catechols can be protected in the presence of phenols as cyclic acetals or ketals, or cyclic esters. Some of the more important phenol and catechol protective groups are included in Reactivity Chart 4 (Chapter 10).
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The acidity constants of meta- and para-substituted phenols and benzenethiols in 20% water–ethanol were measured at 20°. The pKa values range for meta-substituted phenols from 8·58 to 10·42, and for para-substituted phenols from 9·76 to 10·90. For meta-substituted benzenethiols these values range from 6·07 to 6·99 and for para-substituted benzenethiols from 6·53 to 7·47. The Hammett ρ parameter is found to be 2·463 for phenols and 1·81 for benzenethiols. The σ and σR values derived from the Hammett empirical relation indicate significant differences in conjugative effect between the corresponding phenols and benzenethiols having strongly mesomeric para-substituents such as NMe2, NH2, and OMe.
Hammett equation
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