The alkaline hydrolysis of flavonoid glycosides

Conclusions 1. The alkaline hydrolysis of flavonoid glycosides has been studied.2. In an alkaline medium 3-glycosides, C-glycosides, and biosides having 1, 2 bonds between the sugars are stable.3. The difference in the stabilities of the glycosides to alkalis can be used in studying flavonoid O-diglycosides, O-biosides with different positions of the bond, O,C-diglycosides, and O,C-biosides.Khimiya Prirodnykh Soedinenii, Vol. 5, No. 5, pp. 366–369, 1969     

Kinetics of the alkaline hydrolysis of alkoxyfluoroborate anions

The kinetics of the alkaline hydrolysis of BF₃OR^– anions (R=C₂H₅, C₃H₇) have been investigated. It has been shown that the reaction mechanism includes the solvolytic dissociation of a B-F bond and that the processes resulting in the replacement of the first fluoride ion act as the rate-limiting step. The influence of the electron-donor ability of the substituents on the rate of processes has been studied, and the reactivity of alkoxyfluoroborates has been compared with the data from quantum-chemical calculations of the distribution of the electron density in the anions in the framework of Dewar's MNDO method with complete optimization of the structural parameters.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 1, pp. 123–126, January–February, 1989.We thank Yu. B. Vysotskii for a fruitful discussion of the results.     

Kinetics of the acid and alkaline hydrolysis of Monofluorophosphite

The kinetics of the acid and alkaline hydrolysis of monoflorophosphorous acid has been studied by P-31 NMR and static pH titration over a wide temperature range. The acid catalyzed hydrolysis has a rate constant at 25°C equal to 0.35 dm³ mol^?1 s^?1 and an activation energy of 53 kJ while the alkaline hydrolysis has a rate constant of 4.6 dm³ mol^?1 s^?1 and an activation energy of 42 kJ. When the hydrogen in this compound is replaced by either fluorine or a hydroxyl group, the rates of reaction decrease by two orders of magnitude. © 1994 John Wiley & Sons, Inc.     

Kinetics of the alkaline hydrolysis of 3-sulfolanol phenyl ethers

A scheme for the elimination of aryloxy groups via an ElcB mechanism is proposed on the basis of data on the kinetics of the alkaline hydrolysis of 3-sulfolanol phenyl ethers in H₂O and D₂O.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1200–1203, September, 1974.     

Identification of carbohydrate isomers in flavonoid glycosides after hydrolysis by hydrophilic interaction chromatography

A method for carbohydrate isomers (saccharide units) identification in flavonoid glycosides after hydrolysis by an HPLC system with two detectors (diode array UV-VIS detector and evaporative light scattering detector) was set up in this work. Experimental procedure was optimized with two types of model glycosides, namely rutin and hesperidin. The model glycosides were hydrolyzed to saccharide units and aglycone parts; the aglycone was characterized by its UV-VIS spectrum and the saccharide unit was identified by its retention time and elution profile (anomeric signals). Acidic and enzymatic hydrolyses were compared in the first step of the method; in acidic hydrolysis, trifluoracetic acid was used, while glucosidase, galactosidase, and hesperidinase were used in enzymatic hydrolysis. A complete enzymatic hydrolysis was achieved with hesperidin and neohesperidin, but not with 3-O-glycosides. The method was applied for the identification of a glycone from a glycoside isolated from Polygonum lapathifolium (Polygonaceae sp.).     

Investigation of flavonoid glycosides

Summary 1. The method of differential analysis in the IR region of the spectrum has been used in an investigation of the structure of the carbohydrate part of flavonoid glycosides. This method permits the pyranose and furanose forms of the carbohydrate substituents, the - and -anomers of the pyranosides and other structural features characterizing the nature of the sugars in the glycosides to be determined. The method can also be used to study other glycosides — for example, hydroxyanthraquinone glycosides, furocoumarin glycosides, and cardiac and other glycosides.2. A modified method of comparing molecular rotation has been proposed for determining the configuration of the glycosidic linkages and the size of the oxide rings in the carbohydrate part of the flavonoid glycosides.Khimiya Prirodnykh Soedinenii, Vol. 1, No. 4, pp. 233–241, 1965     

Kinetics of the alkaline hydrolysis of isoproturon in CTAB and NaLS micelles

Kinetics of the alkaline hydrolysis of isoproturon has been studied in the absence and presence of cetyltrimethylammonium bromide (CTAB) and sodium lauryl sulfate (NaLS) micelles. CTAB micelles were found to enhance the rate of reaction, while NaLS micelles inhibited the reaction rate. The reaction obeyed first‐order kinetics in [isoproturon] and was linearly dependent on [NaOH] at lower concentration. The rate of reaction became independent at higher [NaOH]. At lower [NaOH] the reaction proceeded via formation of hydroxide ion addition complex, while at higher [NaOH] the reaction occurred via deprotonation of ? NH? , leading to the formation of isocyanate. The values of k_w, k_m, and K_s were determined by considering the pseudophase ion exchange model. The activation parameters have also been reported. The effect of added salts (NaCl and KNO₃) on the reaction rate has also been studied. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 39: 39–45, 2007     

Kinetics of the alkaline hydrolysis of fenuron in aqueous and micellar media

The kinetics of the hydrolysis of fenuron in sodium hydroxide has been investigated spectrometrically in an aqueous medium and in cationic micelles of cetyltrimethylammonium bromide (CTAB) medium. The reaction follows first‐order kinetics with respect to [fenuron] in both the aqueous and micellar media. The rate of hydrolysis increases with the increase in [NaOH] in the lower concentration range but shows a leveling behavior at higher concentrations. The reaction followed the rate equation, 1/k_obs = 1/k + 1/(kK[OH^?]), where k_obs is the observed rate constant, k is rate constant in aqueous medium, and k is the equilibrium constant for the formation of hydroxide addition product. The cationic CTAB micelles enhanced the rate of hydrolytic reaction. In both aqueous and micellar pseudophases, the hydrolysis of fenuron presumably occurs via an addition–elimination mechanism in which an intermediate hydroxide addition complex is formed. The added salts decrease the rate of reaction. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 638–644, 2007     

Kinetics of the alkaline hydrolysis of bis(chloromethyl)phosphinic esters

Conclusions The kinetics of the hydrolysis of bis (chloromethyl)phosphinic esters was investigated in KOH medium at 10 and 25°. The rate constants are correlated with the steric constants of the leaving groups.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 923–924, April, 1967.     

Kinetics of alkaline hydrolysis of organic esters and amides in neutrally-buffered solution

Reaction rate constants for the hydrolysis of organic esters and amides were determined at temperatures of 100–240°C in aqueous solutions buffered at pH values between 5.5 and 7.3. Experiments are modeled assuming alkaline hydrolysis with a thermodynamic solution model included to account for the temperature dependence of hydroxide ion concentration. In most cases, the ester hydrolysis second order rate constants agree well with published values from experiments in strongly basic solutions at pH values from 11 to 14 and temperatures from 25–80°C, despite the large extrapolations required to compare the data sets. The amide hydrolysis rate constants are about one order of magnitude higher than the extrapolated results from other investigators, but the reaction rate increased proportionally with hydroxide ion concentration, suggesting that an alkaline hydrolysis mechanism is also appropriate. These data establish the validity of the alkaline hydrolysis mechanism and can be used to predict hydrolysis reaction rates in neutrally-buffered solutions such as many groundwater and geothermal fluids.     

Acylated flavonoid glycosides from Barringtonia racemosa

Abstract

Using various chromatographic separations, three new acylated flavonoid glycosides, namely barringosides G–I (1–3), were isolated from the water-soluble extract of Barringtonia racemosa branches and leaves. The structure elucidation was performed by extensive analysis of the 1D and 2D NMR and HR-QTOF-MS data. Of the isolated compounds, barringoside I (3) showed moderate inhibitory effects on LPS-induced NO production in RAW264.7 cells with an IC₅₀ of 52.48?±?1.04?µM.     

Hydrolysis of flavonoid glycosides by fungus enzymes

Chemistry of Natural Compounds -