Logkw Values Research Articles

Estimation of lipophilicity and design of new 17β-carboxamide glucocorticoids using RP-HPLC and quantitative structure-retention relationships analysis

Abstract Eight 17β-carboxamide glucocorticoids with local anti-inflammatory activity were selected and their retention behavior tested in six RP-HPLC systems (I–VI). logkw, a, and φ 0 parameters were calculated and correlation with previously determined logPo/w values was examined. RP-HPLC system IV, which consisted of cyano column and methanol–water mobile phases (50:50, 60:40, 70:30, and 80:20, v/v), was selected as the most reliable for lipophilicity prediction and used for the analysis of chromatographic behavior of remaining fourteen 17β-carboxamide glucocorticoids. Quantitative structure-retention relationships analysis was performed and PLS(logkw) model was selected as the most statistically significant. On the basis of selected model and interpretation of corresponding descriptors, new derivatives with higher logkw values and higher expected lipophilicity were designed.

Određivanje lipofilnosti β-hidroksi-β-arilalkanskih kiselina primenom reverzno-fazne tečne hromatografije pod visokim pritiskom

Lipophilicity parameters (logP) were determined for thirteen synthesized β-hydroxy-β-arilalkanoic acids using reversed phase high performance liquid chromatography. Anti-inflammatory activity and potential selectivity towards cyclooxygenase-2 inhibition of synthetized compounds was assessed. Stationary phase was octadecyl modified (C-18) silicagel, and four used mobile phases contained different amount of methanol. Both synthetized and standard compounds with known logP values (aspirin, ibuprofen, ketoprofen, naproxen and phenanthrene) were tested in a chromatographic system. Using retention times for each standard and synthesized compound logk values (logarithm of capacity factor) were calculated. Intercept on a graph showing dependency of logk from methanol amount in the mobile phase for each compound represents logKw(capacity factor when organic solvent amount is zero). Graph showing linear dependency of logP of standard compounds from experimentally obtained logKw values was plotted. LogP values for synthetized compounds were obtained by interpolation from the plotted graph. Obtained values are in a range from 2.901 to 3.847. The best correlation between experimentally obtained and predicted logP values was using KOWWIN software (R2=0.8864), which makes this software appropriate for predicting logP values of this type of compounds.

Comparative pharmacodynamic analysis of imidazoline compounds using rat model of ocular mydriasis with a test of quantitative structure–activity relationships

Imidazol(in)e derivatives, having the chemical structure similar to clonidine, exert diverse pharmacological activities connected with their interactions with alpha2-adrenergic receptors, e.g. hypotension, bradycardia, sedation as well as antinociceptive, anxiolytic, antiarrhythmic, muscle relaxant and mydriatic effects. The mechanism of pupillary dilation observed after systemic administration of imidazol(in)es to rats, mice and cats depends on the stimulation of postsynaptic alpha2-adrenoceptors within the brain. It was proved that the central nervous system (CNS)-localized I1-imidazoline receptors are not engaged in those effects. It appeared interesting to analyze the CNS-mediated pharmacodynamics of imidazole(in)e agents in terms of their chromatographic and calculation chemistry-derived parameters.In the present study a systematic determination and comparative pharmacometric analysis of mydriatic effects in rats were performed on a series of 20 imidazol(in)e agents, composed of the well-known drugs and of the substances used in experimental pharmacology. The eye pupil dilatory activities of the compounds were assessed in anesthetized Wistar rats according to the established Koss method. Among twenty imidazol(in)e derivatives studied, 18 produced diverse dose-dependent mydriatic effects. In the quantitative structure–activity relationships (QSAR) analysis, the pharmacological data (half maximum mydriatic effect – ED50 in μmol/kg) were considered along with the structural parameters of the agents from molecular modeling. The theoretically calculated lipophilicity parameters, CLOGP, of imidazol(in)es, as well as their lipophilicity parameters from HPLC, logkw, were also considered. The attempts to derive statistically significant QSAR equations for a full series of the agents under study were unsuccessful. However, for a subgroup of eight apparently structurally related imidazol(in)es a significant relationship between log(1/ED50) and logkw values was obtained. The lack of “predictive” QSAR for the whole series of the structurally diverse agents is probably due to a complex mechanism of the ligand–alpha2-adrenergic receptor interactions, which are predominantly of a highly structurally specific polar nature. Such interactions are difficult to quantify with the established chemical structural descriptors, contrary to the less specific, molecular bulkiness-related interactions.

Immobilized Artificial Membrane HPLC Derived Parameters vs PAMPA-BBB Data in Estimating in Situ Measured Blood-Brain Barrier Permeation of Drugs.

The affinity indexes for phospholipids (log kW(IAM)) for 42 compounds were measured by high performance liquid chromatography (HPLC) on two different phospholipid-based stationary phases (immobilized artificial membrane, IAM), i.e., IAM.PC.MG and IAM.PC.DD2. The polar/electrostatic interaction forces between analytes and membrane phospholipids (Δlog kW(IAM)) were calculated as the differences between the experimental values of log kW(IAM) and those expected for isolipophilic neutral compounds having polar surface area (PSA) = 0. The values of passage through a porcine brain lipid extract (PBLE) artificial membrane for 36 out of the 42 compounds considered, measured by the so-called PAMPA-BBB technique, were taken from the literature (P0(PAMPA-BBB)). The values of blood-brain barrier (BBB) passage measured in situ, P0(insitu), for 38 out of the 42 compounds considered, taken from the literature, represented the permeability of the neutral forms on "efflux minimized" rodent models. The present work was aimed at verifying the soundness of Δlog kW(IAM) at describing the potential of passage through the BBB as compared to data achieved by the PAMPA-BBB technique. In a first instance, the values of log P0(PAMPA-BBB) (32 data points) were found significantly related to the n-octanol lipophilicity values of the neutral forms (log P(N)) (r(2) = 0.782) whereas no significant relationship (r(2) = 0.246) was found with lipophilicity values of the mixtures of ionized and neutral forms existing at the experimental pH 7.4 (log D(7.4)) as well as with either log kW(IAM) or Δlog kW(IAM) values. log P0(PAMPA-BBB) related moderately to log P0(insitu) values (r(2) = 0.604). The latter did not relate with either n-octanol lipophilicity indexes (log P(N) and log D(7.4)) or phospholipid affinity indexes (log kW(IAM)). In contrast, significant inverse linear relationships were observed between log P0(insitu) (38 data points) and Δlog kW(IAM) values for all the compounds but ibuprofen and chlorpromazine, which behaved as moderate outliers (r(2) = 0.656 and r(2) = 0.757 for values achieved on IAM.PC.MG and IAM.PC.DD2, respectively). Since log P0(insitu) refer to the "intrinsic permeability" of the analytes regardless their ionization degree, no correction for ionization of Δlog kW(IAM) values was needed. Furthermore, log P0(insitu) were found roughly linearly related to log BB values (i.e., the logarithm of the ratio brain concentration/blood concentration measured in vivo) for all the analytes but those predominantly present at the experimental pH 7.4 as anions. These results suggest that, at least for the data set considered, Δlog kW(IAM) parameters are more effective than log P0(PAMPA-BBB) at predicting log P0(insitu) values for all the analytes. Furthermore, ionization appears to affect differently, and much more markedly, BBB passage of acids (yielding anions) than that of the other ionizable compounds.

Quantitative structure-retention relationship of selected imidazoline derivatives on α1-acid glycoprotein column

The retention behaviour of 22 selected imidazoline drugs and derivatives was investigated on α1-acid glycoprotein (AGP) column using Sørensen phosphate buffer (pH 7.0) and 2-propanol as organic modifier. Quantitative Structure-Retention Relationships (QSRR) models were built using extrapolated logkw values as well as isocratic retention factors (logk5, logk8, logk10, logk12, logk15 obtained for 5%, 8%, 10%, 12%, and 15%, of 2-propanol in mobile phase, respectively) as dependant variables and calculated physicochemical parameters as independant variables. The established QSRR models were built by stepwise multiple linear regression (MLR) and partial least squares regression (PLS). The performance of the stepwise and PLS models was tested by cross-validation and the external test set prediction. The validated QSRR models were compared and the optimal PLS-QSRR model for logkw and each isocratic retention factors (PLS-QSRR(logk5), PLS-QSRR(logk8), PLS-QSRR(logk10), MLR-QSRR(logk12), MLR-QSRR(logk15)) were selected. The QSRR results were further confirmed by Linear Solvation Energy Relationships (LSER). LSER analysis indicated on hydrogen bond basicity, McGowan volume and excess molar refraction as the most significant parameters for all AGP chromatographic retention factors and logkw values of 22 selected imidazoline drugs and derivatives.

Determination of the lipophilicity of 2'-hydroxychalcones by RP HPLC method

Lipophilicity of twelve synthesized chalcones, whose ring B is a ortho, meta or para monosubstituted with alkyl, oxyalkyl groups or halogens was determined by reverse phase liquid chromatography, using octadecyl-functionalized (RP-18) silica gel as a stationary phase and two-component mixture of methanol/water as a mobile phase. Linear dependence of logk? values of the volume fraction of methanol in the mobile phase was determined for all analyzed compounds, with high coefficient of correlation (r > 0.99). Extrapolation of the line to 0% methanol concentration resulted in the capacity factor of chromatographic system where water is the mobile phase (logkw). For five standard substances, chemically similar to chalcones, logkw values were determined under experimental conditions and they were correlated with logP values of those compounds available in the literature. logPEXP values of synthesized chalcones were calculated on the basis of the created standard curve. In order to estimate the relevance of the experimentally obtained logP values for chalcones, correlation of logPEXP values with the logP values obtained through various computational procedures was performed using linear regression analysis. Statistical parameters of dependence showed that the best matching of the results had been achieved with ChemOffice program, suggesting that this program is suitable for calculating logP values of newly-synthesized chalcones, as well as of compounds structurally similar to chalcones.

Reversed-phase liquid chromatography with octadecylsilyl, immobilized artificial membrane and cholesterol columns in correlation studies with in silico biological descriptors of newly synthesized antiproliferative and analgesic active compounds

Reversed-phase liquid chromatography (RPLC) with different stationary phases, i.e., octadecylsilyl, immobilized artificial membrane and immobilized cholesterol, was used to study lipophilicity of 56 newly-designed 7,8-dihydroimidazo[2,1-c][1,2,4]triazin-4(6H)-ones and 2,6,7,8-tetrahydroimidazo[2,1-c][1,2,4]triazine-3,4-diones with potential anti-proliferative, anti-metastatic and analgesic activities. Extrapolated retention parameters that correspond to pure buffer as the mobile phase, i.e., logkw values are used as chromatographic lipophilicities. The lipophilic properties of compounds also are characterized by computed logP values and basic pharmacokinetic descriptors calculated in silico with the use of ACD/Percepta software according to Abraham's linear solvation energy relationship. Chromatographic and partitioning parameters are compared with biological descriptors using principal component analysis (PCA), and similarities and dissimilarities between variables and compounds are described. Highly significant, predictive relationships between biological descriptors and chromatographic parameters are obtained. Reversed parabolic relationships, which have very good statistical quality between various biological descriptors, i.e., logKsc, logKp, logBB, and logKhsa, and the logkw values, indicate the advantages of a cholesterol column in comparison with immobilized artificial membrane and octadecylsilyl stationary phase.

Formation of Sulfonyl Aromatic Alcohols by Electrolysis of a Bisazo Reactive Dye

Five sulfonyl aromatic alcohols, namely 4-((2-hydroxyethyl)sulfonyl)phenol, 4-((2-(2-((4-hydroxyphenyl)sulfonyl)ethoxy)vinyl)sulfonyl)phenol, 4-(ethylsulfonyl)phenol, 4-(vinylsulfonyl)phenol and 5-((4-aminophenyl)sulfonyl)-2-penten-1-ol were identified by LC-ESI-Qq-TOF-MS as products formed by electrolysis of the bisazo reactive dye Reactive Black 5 (RB5). Since electrolyses were performed in an undivided cell equipped with Ni electrodes in alkaline medium, amines like 4-(2-methoxyethylsulfonyl)benzene-amine (MEBA) with m/z 216 were also suspected to be formed due to the plausible chemical reaction in the bulk or the cathodic reduction of RB5 and its oxidation by-products. Aiming to check this hypothesis, a method was used for the preparation of MEBA with 98% purity, via chemical reduction also of the dye RB5. The logP of the synthesized sulfonyl aromatic compounds was calculated and their logkw values were determined chromatographically. These data were discussed in regard to the relationship between hydrophobicity/lipophilicity and toxicity.

The efficiency of RP-TLC for lipophilicity assessment. A comparative study on a series of pyrrolyl-acetic acid derivatives, inhibitors of aldose reductase

The lipophilicity of a series of pyrrolyl-acetic acid derivatives, inhibitors of the aldose reductase enzyme, was assessed by reversedphase thin layer chromatography (RP-TLC). The role of the carbon content of the stationary phase in reproducing the octanol-water partitioning was examined using RP-18F254S and RP-8F254S plates. Retention on RP-8 plates was found to be more uniform, while these plates exhibit some advantages for the lipophilicity assessment of acidic compounds, compared to the most commonly used RP-18 plates. However, in both cases, different energetics between octanol-water partitioning and RP-TLC retention seem to be involved. On both plates the influence of ionization of the acid functional group was found to be more pronounced on retention in comparison with previous findings for basic compounds. Both sets of RMw values were compared with HPLC chromatographic indices, reported previously. They were found to correlate better with logkw values, if the latter have been determined in the pr...

Synthesis, structure elucidation, determination of the lipophilicity and identification of antitumour activities in vitro of novel 3-(2-furanyl)-8-aryl-7,8-dihydroimidazo[2,1-c][1,2,4]triazin-4(6H)-ones with a low cytotoxicity towards normal human skin fibroblast cells

Eleven novel 3-(2-furanyl)-8-aryl-7,8-dihydroimidazo[2,1-c][1,2,4]triazin-4(6H)-ones (12–22) were designed and obtained from appropriate 1-aryl-2-hydrazonoimidazolidines (1–11) by condensation reaction with 2-oxo-2-furanacetic acid and subsequent cyclocondensation of intermediate chain derivatives. IR, 1H NMR and 13C NMR spectra and elemental analyses confirmed the chemical structure of all the synthesized compounds. The reversed-phase HPLC method was optimized and proved to be applicable and reliable for the analysis of these unknown small molecules (12–22). These compounds were chromatographed on octadecyl silica (ODS) stationary phase and their hydrophobic parameters expressed as the logkw values were determined by RP-HPLC, using mixtures of methanol and water as mobile phases with different methanol concentrations. Octane-1-sulfonic acid sodium salt (OSA-Na) and 20% acetate buffer (pH 3.5) was added to the mobile phase (eluent containing 0.01M/L OSA-Na in organic modifier (MeOH)—buffered mobile phase). The high values of regression coefficients (r >0.9841) for all the compounds investigated proved the excellent fit between experimental data and the Snyder–Soczewiński equation. Results obtained from the reversed-phase HPLC were compared both with those theoretically calculated and with those obtained from an ALOGPS 2.1. software by the use of nine different computational methods for estimation of logP. The predicted values of logP by use of AB logP algorithm revealed the best correlation with the experimental logkw values for the investigated solutes, since a good correlation (r=0.7760) between these quantities was found. The majority of novel imidazotriazinones were found to be evidently effective in vitro against human cancerous cells (HeLa and T47D) in an effective concentration of 50μg/mL. Five compounds (13, 15, 16, 18 and 22) revealed remarkable antiproliferative activities and selective cytotoxicities for cancer cells over normal HSF cells. Therefore these ones may be considered as a basis for the design of novel useful non-toxic (13, 15 and 16) and low toxic (18 and 22) anticancer agents.

Evaluation of a reversed-phase column (supelcosil LC-ABZ) under isocratic and gradient elution conditions for estimating octanol-water partition coefficients.

The solvation parameter model is used to identify suitable chromatographic models for estimating the octanol-water partition coefficient for neutral compounds of varied structure by reversed-phase liquid chromatography. The stationary phase Supelcosil LC-ABZ with methanol-water mobile phases affords a series of suitable correlation models for estimating the octanol-water partition coefficient (log KOW) under isocratic and gradient elution conditions. Isocratic separations with mobile phase compositions containing from about 25 to 40% (v/v) methanol provide the most accurate results for log KOW values in the range -0.1 to 4.0. Gradient separations programmed from 5 to 100% (v/v) methanol are suitable for faster separations of compounds with large log KOW values. The standard error in the estimate for the regression models of the predicted log KOW values against literature values are 0.135 log units for the 30% (v/v) methanol-water isocratic system and 0.263 log units for the methanol-water gradient system. Isocratic retention factors predicted from two gradient separations with gradient times of 15 and 45 min afford a poorer fit for the correlation models between log KOW and the estimated retention factors than that of either the above isocratic and gradient models. Plots of the retention factor (log k) as a function of mobile phase composition are generally non-linear. Values of log kw obtained by non-linear extrapolation to a volume fraction of 0% (v/v) methanol do not afford a useful model for estimating log KOW.

Use of OPLC to study the biological activity of organic compounds

Solute capacity factors in pure water, logkw, determined by the new method based on Ościk's equation, are proposed as descriptors of the biological activity of some benzamides. Values of logkw determined by the new method and by parabolic extrapolation were compared with the minimum inhibitory concentration (MIC) of the compounds against six different dermatophytes, and correlations between logkw and log (1/MIC) values of the same substances were analysed. For all the dermatophytes and all the compounds very good linear correlations were obtained for retention factors determined by the method proposed in this study.

STUDY OF THE LIPOPHILICITY OF ARYLPROPIONIC NON-STEROIDAL ANTI-INFLAMMATORY DRUGS. A COMPARISON BETWEEN LC RETENTION DATA ON A POLYMER-BASED COLUMN AND OCTANOL-WATER PARTITION COEFFICIENTS

Molecular lipophilicity can be expressed by log Pow or, more conveniently, by log kw, i.e., determined by the traditional shake-flask technique, or by reversed-phase high performance liquid chromatography (RP-HPLC). Moreover, the unionized form of solutes is usually taken as the reference state for the measurement of lipophilicity. This can be problematic for the RP-HPLC determination of lipophilicity of acidic compounds due to the limited pH operating range of silica bonded phases. The measured dissociation constant values (pKa) of the twelve arylpropionic non steroidal antiinflammatory drugs (NSAIDs) are comprised between 3.80 and 5.70; consequently, the lipophilicities of the unionized forms must be measured at pH below 2. Accordingly, their capacity factors (log kw) were determined on a column packed with a hydrophilic polymethacrylate gel having octadecyl groups. This RP-column allows separations at low pH values of the mobile phase. In practice, the values of log kw are obtained by a series of isocratic measurements at various compositions of binary acetonitrile-water eluents and extrapolation of the relationship between log k and volume fraction of organic solvent, φ, to 100% water. The 1-octanol-water partition coefficients (log Pow) of these NSAIDs were determined by the shake-flask technique using a conventional methodology. A significant linear relationship was obtained between log Pow and log kw with a slope close to unity, indicating similar intrinsic thermodynamic behaviour of these drugs for the two partitioning processes. This excellent correlation prompted us to validate this polymer-based column, to be useful for the determination of other acidic drug lipophilicity.

Use of RP-HPLC on a dynamically coated artificial membrane to predict intestinal absorption of bile acids

The preparation of an HPLC column with a non-covalent immobilized artificial membrane, by dynamic coating of a RP-18 surface with phosphatidylcholine, is described. Passive transport of unconjugated bile acids has been correlated with logkw values resulting from interaction with this biomembrane-like surface.

Liquid Chromatographic Estimation of Octanol/Water Partition Coefficients with a High Efficiency, Nonporous, Ultrasmall Particle Size Reverse Phase Stationary Phase

Abstract HPLC retention data, obtained over a range of organic modifier fractions φ in binary mobile phases, can be used to estimate a compounds octanol/water partition coefficient (log Po/w). Such a determination is facilitated by a high efficiency, low capacity column. The utility of a nonporous, ultrasmall particles size (1.5 μ), C18 stationary phase capable of such performance was assessed using aqueous mobile phases containing either acetonitrile or methanol. In general, compounds were effectively eluted from this stationary phase at lower values of φ than with more typical stationary phases, thus increasing the accuracy and speed with which log Kw, the capacity factor in a 100% aqueous mobile phase, could be determined. Values of log Kw obtained for seventeen model compounds were highly correlated with the compound's log P0/w. Comparison of retention trends in the methanol and acetonitrile mobile phases suggests differences in the retention mechanisms for both organic modifiers.