- Novel method for preparation of monoesters of symmetric diphenolic compounds like curcumin (1,7-bis(4-hydroxy-3-methoxy phenyl)-1,6-heptadiene-3,5- dione) via solid-phase synthesis
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Synthesis of a monoester of symmetrical diphenolic compound curcumin (1,7-bis(4-hydroxy-3-methoxy phenyl)-1,6-heptadiene-3,5-dione) with glycine has been carried out by anchoring one of its free phenolic groups to an insoluble polymeric solid-support resin controlled pore glass-long chain alkylamine (CPG-LCAA) via a 2-carbon linker by solid-phase synthesis. The other free phenolic was esterified selectively with N-protected glycinoyl chloride to give the monoester exclusively. Subsequent deprotection of the amino group and deblocking of the monoester from polymer support by treatment with hydriodic acid (HI) gave the desired product. We earlier reported synthesis of a large number of diesters of curcumin, but selective esterification of one phenolic has been accomplished by this novel method, which can be used for preparing monoesters of any symmetric diphenol in quantitative yields. Copyright Taylor & Francis Group, LLC.
- Dubey, Shiv Kumar,Dwivedi, Vishnu,Misra, Krishna
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p. 4265 - 4271
(2008/03/13)
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- Syntheses, antifeedant activity, and QSAR analysis of new Oxa(thia)diazolyl 3(2H)-pyridazinones
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Twenty-eight new oxa(thia)diazolyl 3(2H)-pyridazinone derivatives were synthesized. Some compounds showed good chronic growth activities against the armyworm, Pseudaletia separata (Walker). Their EC50 values were determined in vivo. Nineteen 2-
- Cao, Song,Wei, Na,Zhao, Chuanmeng,Li, Lina,Huang, Qingchun,Qian, Xuhong
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p. 3120 - 3125
(2007/10/03)
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- Chemistry of diazopolycarbonyl compounds: V. Synthesis, structure, and chemical characteristics of aryl diazoacetates
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Aryl diazoacetates were prepared, and basing on spectral data and quantum-chemical calculations cis-trans isomerism thereof was proved. The reactions of diazoesters with hydrochloric and sulfuric acids, triphenylphosphine, and dinitrogen tetroxide resulted respectively in aryl chloroacetates, bis(aryloxy-carbonylmethyl) sulfates, triphenylphosphoranylidenehydrazones of aryl 2-oxoethanoates, and N-oxides of diaryl 1,2,5-oxadiazole-3,4-dicarboxylates.
- Zalesov,Kataev
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p. 1666 - 1672
(2007/10/03)
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- Kinetics of the pH-independent hydrolysis of 4-nitrophenyl chloroformate in aqueous micellar solutions: Effects of the charge and structure of the surfactant
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The pH-independent hydrolysis of 4-nitrophenyl chloroformate in the presence of aqueos micelles of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, alkyltrimethylammonium chlorides, alkyldimethylbenzylammonium chlorides (alkyl group = cetyl and dodecyl) and polyoxyethylene (9) nonylphenyl ether was studied spectrophotometrically. The observed rate constants, kobs, decrease in the following order: cationic micelles > bulk water > non-ionic micelles > anionic micelles. Surfactant-substrate association constants, Ks, were determined from the dependence of kobs on surfactant concentration, and were found to be only slightly dependent on the charge of the surfactant and, for similarly charged micelles, on the length of their hydrophobic tail. A 1H NMR study of the solubilzation of a model compound, 4-nitrophenyl chloroacetate, showed that all surfactant segments are affected by the solubilizate and the effect is more pronounced toward the middle of the hydrocarbon chain. The average solubilization site of the acetate ester does not depend on the charge of the micelle or the length of the surfactant hydrophobic tail. Micellar effects on observed rate constants are analyzed in terms of a 'medium' effect and an 'electrostatic' effect. The lower microscopic polarity at the reaction site retards the reaction, whereas electrostatic interactions of the polar transition state with the charged interface result in a rate decrease by anionic micelles and a rate enhancement by cationic micelles. Copyright
- Possidonio, Shirley,Siviero, Fabio,El Seoud, Omar A.
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p. 325 - 332
(2007/10/03)
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- New liquid crystal derivatives of thiazole
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2-(4′-Alkoxybenzylidenamino)-4-(4-nitrophenoxy)thiazoles, which possess monotropic mesomorphism of the nematic type over the range 68-160°C, have been synthesized. 1996 Plenum Publishing Corporation.
- Murza,Golovanov,Safarov
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p. 477 - 478
(2007/10/03)
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- Effect of the acyl group in the reaction of imidazole with acyl-substituted 4-nitrophenyl acetates in acetonitrile and in aqueous acetonitrile with a low water content
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Reactions of imidazole with 4-nitrophenyl chloroacetate and dichloroacetate have been studied in acetonitrile and in 0.56 mol dm-3 water in acetonitrile.The second-order dependence, beside the first-order term in imidazole, is observed for all
- Neuvonen, Helmi
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p. 951 - 954
(2007/10/02)
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- ENAMINONES IN THE PREPARATION OF 1,2-DIAZETIDIN-4-ONES
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A new procedure for the preparation of 1,2-diazetidin-4-ones via ring closure of N1-(2-chloroacyl)-N1-methyl-N2-(3-oxocyclohexenyl)hydrazines has led to the preparation of a 4,4-disubstituted 1,2-diazetidin-4-one.
- Greenhill, John V.,Taylor, Edward C.
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p. 2417 - 2427
(2007/10/02)
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- General Base Catalysis in the Methanolysis of 4-Nitrophenyl Acetates
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The rates of methanolysis of 4-nitrophenyl acetate, chloroacetate, and dichloroacetate have been measured in the presence of pyridines and imidazoles.Methyl substitution at the 2- and 6-positions in pyridine causes only a slight reduction in reactivity.A
- Neuvonen, Helmi
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p. 669 - 673
(2007/10/02)
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- pKa VALUES OF 2- AND 2,6-DISUBSTITUTED PYRIDINE DERIVATIVES CONTAINING SULFENYL AND SULFINYL GROUPS AND ?* AND ES VALUES OF SEVERAL SULFENYL AND SULFINYL GROUPS
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pKa Values of pyridine derivatives having sulfenyl and sulfinyl groups attached to either 2- or 2,6-positions in the pyridine nuclei were measured affording the following values; 2-SCH3 (3.64), 2-S(O)CH3 (0.17), 2-CH2SCH3 (5.40), 2-CH2S(O)CH3 (3.10), 2-CH2OCH3 (4.35), 2,6-(SCH3)2 (2.37), 2,6-(CH2SCH3)2 (4.10), 2,6-(CH2S(O)CH3)2 (1.53), 2,6-(CH2OCH3)2 (3.50).These pKa values together with several other 2-substituted pyridines: 2-X-C5H4N in which X is Cl, Br, I, CN, CO2C2H5, CH3, H, OCH3, were plotted against Taft ?* values to afford a good straight line giving ρ*= -4.5.From fitting the above pKa values on this line, the ?* values of these groups were determined.Furthermore, Es values of CH3S(O)-, CH3SCH2-, CH3S(O)CH2- CH3OCH2-groups were determined and the application of the ?* values was tested by measuring both acid and alkaline hydrolyses rates of the corresponding p-nitrophenyl acetates, the modified Taft method.The additivity of these ?* values in the 2,6-positions in the pyridine nuclei was examined.The cation-transfer experiments were undertaken by using 2,6-bis(methylsulfinylmethyl)pyridine as mediator.
- Furukawa, Naomichi,Iida, Keiko,Kawai, Tsutomu,Ogawa, Satoshi,Oae, Shigeru
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p. 239 - 254
(2007/10/02)
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- Acyl Substituent Effects on Rates of Acyl Transfer to Thiolate, Hydroxide, and Oxy Dianions
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The rates of transfer of a series of polar aliphatic acyl groups (-0.3 (*) (*) (*) 1.05) from p-nitrophenol to hydroxide, to the thiol anion of N-acetyl-L-cysteine, and to a series of phosphonate dianions have been determined in aqueous solution.The rate constants for the alkaline hydrolysis of ten p-nitrophenyl esters can be correlated reasonably well (r = 0.981) to the single-parameter Hammett-Taft equation based on the polar substituent constant.The reaction constant for the alkaline hydrolysis is (*) = 2.9 with an interval estimator (90percent confidence) of +/-0.3.The (*) value for the thiolysis reaction is only slightly larger (16 +/- 13percent) than the corresponding value for the alkaline hydrolysis reaction.These kinetic (*) values are essentially identical with the equlibrium (*) for hydroxide or thiolate addition to aldehydes (Kanchuger and Byers).To the extent that gem diolate and thiohemiacetalate formation are appropriate model reactions for the formation of the anionic tetrahedral intermediates in the corresponding acyl transfer reactions, the magnitude of the kinetic (*) values suggests that the transition states for the alkaline hydrolysis and for the thiolysis reactions are similar, in geometry and charge distribution, to the intermediates.Acyl transfer from p-nitrophenol to phosphonate dianions involves an uncatalyzed nucleophilic displacement by the oxy dianion.The (*) value for the reaction of (chloromethyl)phosphonate with the p-nitrophenyl esters is 2.4 (+/-0.3).The second-order rate constants for the reactions between the phosphonates and p-nitrophenyl acetate, p-nitrophenyl chloroacetate, and p-nitrothiophenyl acetate show a small sensitivity to the basicity (pKa2) of the nucleophile (βnuc ca. 0.3).An explanation of the magnitudes of the (*) and βnuc values, and of the anomalously low reaction rates (relative to oxy monoanions and amines of comparable basicities) for acyl transfer to the phosphonates, is that electrostatic interactions and desolvation of the oxy dianion make substantial contributions to the activation energy barrier for nucleophilic attack.
- Shames, Spencer L.,Byers, Larry D.
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p. 6170 - 6177
(2007/10/02)
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