Meta-substituted Benzoic Acids Research Articles

Investigation of the requirements for efficient and selective cytochrome P450 monooxygenase catalysis across different reactions

The cytochrome P450 metalloenzyme (CYP) CYP199A4 from Rhodopseudomonas palustris HaA2 catalyzes the highly efficient oxidation of para-substituted benzoic acids. Here we determined crystal structures of CYP199A4, and the binding and turnover parameters, with different meta-substituted benzoic acids in order to establish which criteria are important for efficient catalysis. When compared to the para isomers, the meta-substituted benzoic acids were less efficiently oxidized. For example, 3-formylbenzoic acid was oxidized with lower activity than the equivalent para isomer and 3-methoxybenzoic acid did not undergo O-demethylation by CYP199A4. The structural data highlighted that the meta-substituted benzoic acids bound in the enzyme active site in a modified position with incomplete loss of the distal water ligand of the heme moiety. However, for both sets of isomers the meta- or para-substituent pointed towards, and was in close proximity, to the heme iron. The absence of oxidation activity with 3-methoxybenzoic acid was assigned to the observation that the CH bonds of this molecule point away from the heme iron. In contrast, in the para isomer they are in an ideal location for abstraction. These findings were confirmed by using the bulkier 3-ethoxybenzoic acid as a substrate which removed the water ligand and reoriented the meta-substituent so that the methylene hydrogens pointed towards the heme, enabling more efficient oxidation. Overall we show relatively small changes in substrate structure and position in the active site can have a dramatic effect on the activity.

Liquid chromatography/isotope ratio mass spectrometry analysis of halogenated benzoates for characterization of the underlying degradation reaction in Thauera chlorobenzoica CB-1T.

Halogenated benzoic acids occur in the environment due to their widespread agricultural and pharmaceutical use. Compound-specific stable isotope analysis (CSIA) has developed over the last decades for investigation of in situ transformation and reaction mechanisms of environmental pollutants amenable by gas chromatography (GC). As polar compounds are unsuitable for GC analysis we developed a method to perform liquid chromatography (LC)/CSIA for halogenated benzoates. LC/isotope ratio mass spectrometry (IRMS) utilizing a LC-Surveyor pump coupled to a MAT 253 isotope ratio mass spectrometer via a LC-Isolink interface was applied. For chromatographic separation a YMC-Triart C18 column and a potassium hydrogen phosphate buffer (150mM, pH7.0, 40°C, 200μL mL-1 ) were used, followed by wet oxidation deploying 1.5molL-1 ortho-phosphoric acid and 200g L-1 sodium peroxodisulfate at 75μL mL-1 . Separation of benzoate and halogenated benzoates could be achieved in less than 40min over a concentration range of 2 orders of magnitude. Under these conditions the dehalogenation reaction of Thauera chlorobenzoica 3CB-1T using 3-chloro-, 3-bromo- and 4-chlorobenzoic acid was investigated resulting in inverse carbon isotope fractionation for meta-substituted benzoic acids and minor normal fractionation for para-substituted benzoic acids. Together with the respective growth rates this led to the assumption that dehalogenation of para-halobenzoic acids follows a different mechanism from that of meta-halobenzoic acids. A new LC/IRMS method for the quantitative determination of halogenated benzoates was developed and used to investigate the in vivo transformation pathways of these compounds, providing some insights into degradation and removal of these widespread compounds by T. chlorobenzoica 3CB-1T .

Theoretical study of the energetics of carboxylic O–H bond cleavage in the para- and meta-substituted benzoic acid derivatives

Abstract Gas phase bond dissociation enthalpies (BDE) of para- and meta-substituted benzoic acids and proton affinities (PA) of their carboxylate anions were investigated using the B3LYP/6-311++G** method for 15 substituents with various electron-donating and electron-withdrawing effects. The employed computational method provided BDE and PA values in fair agreement with experimental data. The substituent effect on BDEs and PAs was analyzed in terms of Hammett constants. Found dependences exhibit satisfactory linearity and enable quick estimation of BDEs and PAs from the Hammett constants.

Is the Hammett’s Constant Free of Steric Effects?

In this work, we have explored the validity of the hypotheses on which rest the Hammett's approach to quantify the substituent effect on a reaction center, by applying two DFT energy decomposition schemes. This is performed by studying the change in the total electronic energy, ΔΔE, associated with a proton transfer isodesmic equilibrium. For this reaction, two sets of substituted benzoic acids and their corresponding benzoate anions have been considered. One of these sets contains para- and meta-substitutions, whereas the other one includes ortho-substituted benzoic acids. For each case, the gas phase change in the total electronic energy has been calculated, and two DFT energy decomposition schemes have been applied. The experimental σ(X) was found to be nearly proportional to the computed ΔΔE. The results for the para- and meta-substituted benzoic acids lead to the conclusion that it is possible to treat separately and, in an additive manner, the electrostatic and steric contributions; and also that the Hammett constant depends mainly on the electronic contributions to the free energy, while the steric contribution is negligible. However, the results for the ortho-substituted cases lead to the conclusion, as was assumed by Hammett, that there are significant qualitative differences between the effects on a reaction site of substituents in the meta- and para-positions and those in the ortho-position.

Dual Dehydrosqualene/Squalene Synthase Inhibitors: Leads for Innate Immune System‐Based Therapeutics

Dual Dehydrosqualene/Squalene Synthase Inhibitors: Leads for Innate Immune System‐Based Therapeutics

Influence of Aprotic Solvents on the Transmission of Anomalous Substituent Effects on 13C NMR Chemical Shifts at the Carboxyl Carbon (δco) in Meta-Substituted Benzoic Acids: A Strong Evidence for π-Polarization Mechanism

Anomalous (reverse) substituent-induced 13C nuclear magnetic resonance chemical shifts at the carboxyl carbon (δco) in meta-substituted benzoic acids have been studied for 11 substituents having varying electronic effects in 4 aprotic (nonhydroxylic) solvents of varying polarity by employing different dual substituent parameter models. The regression results for apolar aprotic solvents provide a strong evidence for through space π-polarization mode of transmission of reverse meta-substituent effects on the carboxyl carbon in benzoic acids. The results for dipolar aprotic solvents indicate significant specific solvation of π-polarized forms of the acids. The study showed further that an apolar aprotic solvent has a distinct preference over a dipolar aprotic one for investigating intrinsic substituent effects on chemical shifts in aromatic molecules.

Kinetics of proton transfer between metasubstituted benzoic acids and the carbinol base of crystal violet in toluene: Specific solvent effect–free metasubstituent effect on the reactivity of benzoic acids

AbstractApolar aprotic solvents are particularly advantageous for investigating the intrinsic metasubstituent effect free from complications of specific solvent effects. A kinetic study for toluene‐phase proton transfers between meta‐Me, F, Cl, Br, I, OMe, OPh, COPh, CF3, CN, NO2, H benzoic acids and Crystal Violet carbinol base has shown the forward rate constant (log k1) the most appropriate reactivity parameter in toluene. log k1 (toluene) as compared to other reported reactivity parameters in benzene or toluene have been found more sensitive to the metasubstituent effect. The regression results of the correlation of log k1 (toluene) of the acids according to the four dual substituent parameter models are statistically significant, and the best result has been obtained using Taft's model. The overall analysis reveals that metasubstituent's effect is exerted by a 65:35 pattern of its field and second‐order resonance effects. The results further demonstrate that a metasubstituent's resonance effect is virtually a relayed universal field/inductive effect. © 2011 Wiley Peiodicals, Inc. Int J Chem Kinet 43: 303–311, 2011

Origin and Nature of Transmission Modes of Anomalous Effects of meta-Substituents on the 13C Chemical Shift of the Carboxyl Carbon (δCO) of Benzoic Acid

Studies of substituent effects on NMR chemical shifts are of great benefit in determining fine details of electron distribution in molecules. Interestingly, NMR substituent effects are often different and even opposite to those associated with chemical reactivity. Among molecules exhibiting anomalous (reverse) substituent effects is benzoic acid, the standard model for studying substituent effects. The substituent effect on the 13C chemical shift of its carboxyl carbon (δ CO) is just the opposite of that on its acid strength or reactivity. To develop insights into the origin of the anomalous effect of a substituent on δ CO, occupancies of natural atomic orbitals at the carboxyl and ring carbons of a set of 10 meta-substituted benzoic acids have been calculated at the density functional theory level using the B3LYP function with split valance 6–311G++** basis set. Statistical correlations obtained for the 13C chemical shifts, δ CO and δ C-ring of these benzoic acids with the natural atomic orbital occupancies calculated for respective carbon atoms on one hand and with Taft’s inductive and resonance parameters (σ I and σ R BA ) of the substituents on the other hand have been critically analyzed. The findings have established firmly that a meta-substituent’s anomalous effect on δ CO is caused by the substituent-induced changes in the total occupancy of only the p z natural atomic orbitals at the carboxyl carbon. The study has demonstrated further that the transmission of the anomalous effect can be successfully interpreted by a 5.5:–2.5:1 combination of the localized, extended, and resonance-induced π-polarization effects.

Molecular Recognition in Proton-Transfer Compounds of Brucine with Achiral Substituted Salicylic Acid Analogues

The 1:1 proton-transfer brucinium compounds from the reaction of the alkaloid brucine with 5-nitrosalicylic acid, 3,5-dinitrosalicylic acid, and 5-sulfosalicylic acid, namely anhydrous brucinium 5-nitrosalicylate (1), brucinium 3,5-dinitrosalicylate monohydrate (2), and brucinium 5-sulfosalicylate trihydrate (3) have been prepared and their crystal structures determined by X-ray crystallography. All structures further demonstrate the selectivity of brucine for meta-substituted benzoic acids and comprise three-dimensional hydrogen-bonded framework polymers. Two of the compounds (1 and 3) have the previously described undulating brucine sheet host-substructures which incorporate interstitially hydrogen-bonded salicylate anion guest species and additionally in 3 the water molecules of solvation. The structure of 2 differs in having a three-centre brucinium–salicylate anion bidentate N+–H···O(carboxyl) hydrogen-bonding association linking the species through interstitial associations involving also the water molecules of solvation. A review of the crystallographic structural literature on strychnine and brucine is also given.

Réactions d'ortho lithiation de composés benzéniques et hétéroaromatiques-π-excédentaires dirigées par la fonction acide carboxylique

This review surveys and classifies the lithiations of aromatic and π-excessive heteroaromatic systems directed by the carboxylic acid group. Treatment of a benzoic acid with 2.2 equivalents of the 1:1 complex sec-butyllithium·tetramethylethylene diamine in THF at −90°C gives an ortho metallated species stable at low temperatures (−78°C) which may be quenched with various electrophiles. These reactions are capable of producing novel functionalities ortho to the carboxylic acid group and do not require protection-deprotection techniques. In contrast with a few exceptions, lithiation of meta-substituted benzoic acids permits the regioselective preparation of 2,3-disubstituted derivatives. Alternatively, 2,3-disubstituted benzoic acids are readily available by lithiating 1,2-disubstituted compounds, metallation occurring ortho to the more effective directing group. In turn the 2,3-disubstituted benzoic acids can be utilized to prepare 2,3,4- or 2,3,6-trisubstituted benzoic acids, etc. Lithiations in the position ortho to the carboxylic acid group have also been reported on heteroatomic systems. Thiophens and furans substituted by a carboxylic acid group may be lithiated and the site of metallation depends on the nature of the deprotonating agent.

Potential for carboxylation-dehydroxylation of phenolic compounds by a methanogenic consortium.

An anaerobic consortium that carboxylated and dehydroxylated phenol to benzoate, and 2-cresol to 3-methylbenzoic acid, under methanogenic conditions was studied. Phenol induced this transformation activity. Addition of 4-hydroxypyridine or an increase in the concentration of proteose peptone to 0.5% (w/v) delayed the transformation. Phenol enhanced the rate of transformation of 2-cresol whereas 2-cresol delayed the transformation of phenol. Phenols with ortho-substitutions (chloro-, fluoro-, bromo-, hydroxyl-, amino-, or carboxyl-) were transformed to meta-substituted benzoic acids. However, meta- and para-substituted phenols (cresols, fluorophenols, and chlorophenols) were not transformed. Phenol was most rapidly metabolized, followed by catechol, 2-cresol, 2-fluorophenol, 2-aminophenol, 2-chlorophenol, 2-hydroxybenzoic acid, and 2-bromophenol. The consortium O-demethylated anisole to phenol and 2-methoxyphenol to catechol, and oxidized 2-hydroxybenzyl alcohol to 2-hydroxybenzoic acid. Aniline, 2-ethylphenol, 2-hydroxypyridine, 2-acetamidophenol, 2,6-dimethylphenol, 2-phenylphenol, and 1-naphthol were not metabolized.

Optimization of molecular geometry of meta-substituted benzoic acids and their anions by gradient CNDO/2 method

32 conformers of meta-substituted benzoic acids I and the corresponding anions II have been optimized with respect to all geometrical degrees of freedom by the title semiempirical MO approach. The calculated geometry characteristics are compared with some published data obtained by means of X-ray diffraction.

Thin Layer Chromatographic Separation of Ortho, Meta, and Para Substituted Benzoic Acids and Phenols with Aqueous Solutions of α-Cyclodextrin

Abstract The use of aqueous solutions of α-cyclodextrin as the mobile phase in thin layer chromatography (TLC) is described. A series of eighteen substituted benzoic acid compounds were chromatographed on polyamide thin layer sheets. The Rf values were dependent on the concentration of α-cyclodextrin in the mobile phase as well as the structure and size of the individual molecules. Possible advantages of this technique over those which use pure or mixed solvent systems as the mobile phase are discussed.

Investigation of pyrimidine-4-carboxylic acids

The effect of various substituants in the 6 position on the ionization constants of pyrimidine-4-carboxylic acids was studied and compared with the effect of substituents on the dissociation constants of the corresponding meta-substituted benzoic acids.