- Substituent effects on energetics of peptide-carboxylate hydrogen bonds as studied by 1H NMR spectroscopy: Implications for enzyme catalysis
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Substituent effects in N-H···O hydrogen bonds were estimated by comparing the acidities of two series of model compounds: N-benzoylanthranilic acids (A) and 4-benzoylamidobenzoic acids (B). Intramolecular N-H···O hydrogen bonds were found to be present in the A series of compounds, while B acids were used as control models. The respective pKa values for A and B acids were determined experimentally in DMSO solution using proton NMR spectroscopy. With X = H, the pKa for A and B acids were observed to be 7.6 and 11.6, respectively, a difference of 4.0 units (ΔpKa). However, with X = p-NO 2, the ΔpKa value between A and B acids increased to 4.7 units: the pKa values for A and B acids were determined as 6.7 and 11.4, respectively. The ΔpKa values between A and B acids as a function of the X substituents were studied in 10 other examples. The effects of X substituents in A acids could be predicted on the basis of the observed linear Hammett correlations, and the sensitivity of each substituent effect was found to be comparable to those observed for the ionization of substituted benzoic acids (ρ = 1.04 for A acids, and ρ = 1.00 for benzoic acids).
- Emenike, Bright U.,Liu, Albert Tianxiang,Naveo, Elsy P.,Roberts, John D.
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- Ru-based complexes as heterogeneous potential catalysts for the amidation of aldehydes and nitriles in neat water
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Five novel heterogeneous mononuclear complex-anchored Ru(III) have been efficiently sono-synthesized and characterized by utilizing several analytical techniques. The assembled complexes could be utilized as effective, robust and recyclable (up to eight consecutive runs) catalysts for one-pot transformation of a vast array of nitriles and aldehydes to primary amides in H2O under aerobic conditions. Moreover, some unreported di- and tetra-amide derivatives were obtained also under the optimal conditions. The results of ICP/OES analysis demonstrated that there is no detected leaching of the recycled catalyst, which suggests the real heterogeneity of the present protocol. The present Ru-complexes exhibited superiority compared to other reported catalysts for amide preparation in terms of low catalyst load, short reaction time, low operating temperature, no hazardous additives required, and high values of TON (990) and TOF (1980 h11).
- Arafa, Wael Abdelgayed Ahmed
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supporting information
p. 1056 - 1064
(2020/11/09)
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- Palladium catalyzed chemo- and site-selective C-H acetoxylation and hydroxylation of oxobenzoxazine derivatives
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An efficient protocol for the introduction of acetoxy and hydroxy functionalities on unactivated aryl sp2 carbons of oxobenzoxazine derivatives via an ortho-C-H activation reaction using a palladium catalyst has been developed for the first tim
- Bakthadoss, Manickam,Vijay Kumar, Polu,Kumar, Ravan,Agarwal, Vishal
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p. 4465 - 4469
(2019/05/16)
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- Synthesis and luminescence properties of 3,1-benzoxazine and quinazoline derivatives
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2-(2-Hydroxyphenyl)-3,1-benzoxazin-4-one and 2-(2-hydroxyphenyl)-3-isopropylquinazolin-4(3H)-one were synthesized, and their structure was studied by NMR, IR, and UV spectroscopy. Absorption and luminecence properties of these compounds in various solvents were studied by stationary UV and luminescence spectroscopy. They were shown to exist in two isomeric forms (trans and cis) due to rotation about the C-C bond. Excitation at the absorption band of the cis structure with intramolecular hydrogen bond results in intramolecular proton transfer in the singlet excited state with formation of nonpolar oxo form which is responsible for fluorescence with an anomalous Stokes shift. * This study was financially supported by the Russian Foundation for Basic Research (project no. 97-03-32017a).
- Ivakhnenko,Kharlanov,Maksimenko,Knyazhanskii
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p. 123 - 127
(2007/10/03)
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- Novel synthesis of dianthalexin (Phytoalexin) analogues preparation
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Two phytoalexins, previously isolated from carnation infected by Phytophthora parasitica D., were synthesized: 2-phenyl-7-hydroxy-4H-3,l-benzoxazin-4-one (Dianthalexin) and 2-(2-hydroxybenzoyl)-amino-4-methoxybenzoic acid (Dianthramide A). The first one w
- Hauteville,Ponchet,Ricci,Favre-Bonvin
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p. 715 - 718
(2007/10/02)
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