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RP-TLC retention behavior has been studied for a series of potential antituberculotic drugs from a group of substituted anilides of pyrazine-2-carboxylic acid. Lipophilicity was determined by use of reversed-phase thin-layer chromatography with methanol-water mobile phases. R MW values were obtained by extrapolation of R M (determined by RP-TLC) to methanol-free conditions. These experimental lipophilicity values were correlated with lipophilicity (log P ) calculated by use of three software products. Good correlation was obtained between R MW and log P . The results of this study could be used in further experiments focused on investigation of the biological activity of these newly prepared compounds and other potential antituberculotic drugs with closely similar chemical structures.

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Acta Chromatographica
Authors: M. Waksmundzka-Hajnos, D. Matosiuk, A. Petruczynik, and U. Kijkowska-Murak

Summary

Nine alkaloids were chromatographed by reversed phase (RP) TLC on RP-18 with aqueous acetone or aqueous dioxane mobile phases. A variety of mobile phase additives (ammonia, diethylamine (DEA), tetrabutylammonium chloride (TBA-Cl)) were used to suppress ionization of the alkaloids and/or reduce ionic interactions with surface silanol groups. Ion-pair (IP) RP-TLC was also performed with aqueous acetone mobile phases and reagents such as pentane sulphonic acid (PSA), octane sulphonic acid (OSA), or di-(2-ethylhexyl)orthophosphoric acid (HDEHP) as mobile phase additives. In these systems retention of the alkaloids was determined using mobile phases with different modifier concentrations. Relationships between R M and modifier concentration were sought. A linear semilogarithmic equation was fitted to experimental data and used to obtain lipophilicity values R MW (R M for pure water), the slope (S), and ϕ 0, the intercept with the x-axis. The retention of standards with known lipophilicity log P was then determined using the chromatographic systems described above and R MW values were calculated. From these experimental data equations relating log P and R MW were created for each system separately and these equations were used to estimate log P exp values for the alkaloids. log P exp, slope (S), and ϕ 0 values obtained by use of different TLC systems were also correlated.

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log P values of 29 biologically active chalcone (1) and cyclic chalcone analogues E -2-(X-benzylidene)-1-indanones (2) and E -2-(X-benzylidene)-1-tetralones (3) have been determined by an optimized and validated RP-TLC method. RP-TLC was performed on silanized silica gel 60F 254 as stationary phase with methanol-water, 60 + 40 ( v/v ) as mobile phase. The RP-TLC method was validated by analysis of three drugs, diazepam, progesterone, and PGE 1 ethyl ester, with known log P SF (shake-flask) values. The experimentally determined log P TLC values were compared with the log P values predicted by use of the CLOGP program. On the basis of the log P TLC values of the investigated chalcones (1), the cyclic chalcone analogues (2, 3), and previously investigated, related, E -2-(X-benzylidene)-1-benzosuberones (4) the effect on lipophilicity of ring size and the nature and position of substituents were studied. It was found that the open-chain chalcones (1) and the five-membered ring E -2-(X-benzylidene)-1-indanones (2) have similar lipophilicity. Changing the ring size from five to six (3) and from six (3) to seven (7) resulted in the expected increase of the log P values of the compounds. The results indicate importance of steric and electronic factors in the lipophilicity of the compounds investigated.

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Phenol and its methyl derivatives have been separated by RP-TLC on RP-2 plates with three mobile phases. R M values, toxicity (log 1/ C ), p K a values, and partition coefficients of the phenols were correlated with the numerical values of electrotopological states (SaasC, SaaCH, and SsOH). It was found that SaasC and SaaCH described R M , toxicity, and the experimental and theoretical partition coefficients better than SsOH, whereas SsOH best described the p K a values of the phenols. The equations introduced in this paper can be used to predict R M , toxicity, p K a , and partition coefficients for compounds omitted during derivation of the correlation equations.

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Pioglitazone hydrochloride is an oral anti-hyperglycemic agent used for treatment of type-II diabetes. This paper reports a stability-indicating densitometric RP-TLC method for analysis of pioglitazone hydrochloride in the bulk material and in pharmaceutical formulations. Use of aluminum foil plates coated with silica gel 60 RP-18 F 254 s and acetone-water-acetic acid 4:1:0.1 ( ν/ν ) as mobile phase resulted in a compact band for pioglitazone hydrochloride ( R F 0.68 ± 0.02). UV densitometric detection was performed at 225 nm. The method was highly sensitive with good linearity over the concentration range 500–3000 ng per band. The method was validated for accuracy, precision, recovery, and robustness. LOD and LOQ were 46.62 and 141.30 ng, respectively. Pioglitazone hydrochloride was subjected to acid and alkaline hydrolysis, oxidation, and photochemical and thermal degradation. The drug was degraded under all these conditions. Statistical analysis proved the method enabled repeatable, selective, and accurate analysis of the drug. Because the method could effectively separate the drug from its degradation products, it can be regarded as stability-indicating.

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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 R Mw values were compared with HPLC chromatographic indices, reported previously. They were found to correlate better with logk w values, if the latter have been determined in the presence of noctanol as mobile phase additive. In all cases, best relationships were obtained with R Mw(C18). The performance of R Mw indices in regression equations modeling the aldose reductase inhibitory activity was evaluated. Results were comparable with those previously generated using logP. Both R Mw(C8) and R Mw(C18) proved to perform equally well as lipophilicity indices in correlating biological activity, if combined with the ionization correction term Q and Abraham’s basicity term B as additional parameters.

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The relative lipophilicity (
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) of fourteen 1-substituted pyrrolidin-2-one derivatives has been measured by use of RP-TLC plates and mixtures of acetonitrile and pH 7.0 Tris buffer with volume fractions of acetonitrile between 20 and 80% were used as mobile phases. Retention data ( R M ) obtained by this method were exponentially dependent on acetonitrile concentration and enabled estimation of the relative lipophilicity corresponding to pH 7.0 Tris buffer as mobile phase. 1-{2-Hydroxy-3-[4-(3-methoxyphenyl)piperazin-1-yl]propyl}pyrrolidin-2-one had the highest relative lipophilicity (1.33) and butylcarbamic acid 1-[4-(2-methoxyphenyl)piperazin-1-ylmethyl]-2-(2-oxopyrrolidin-1-yl)ethyl ester had the lowest (0.72). Comparison of
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values obtained with the affinity of the compounds tested for α-adrenoceptors enable formulation of preliminary equations for quantitative structure-activity relationships (QSAR).
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log P values of 14 biologically active (E)-3-(X-benzylidene)-2,3-dihydro-1-benzopyran-4-ones (3) have been determined by an optimized and validated reversed-phase thin-layer chromatography (RPTLC) method. The RP-TLC investigations were performed on silanized silica gel 60F254 as stationary phase with methanol-water 60:40 (v/v) as mobile phase. The RP-TLC method was validated by analysis of four drugs, diazepam, progesterone, PGE1 ethyl ester, and itraconazole, with known log P SF (shake-flask) values. The experimentally determined log P TLC values were compared with the predicted log P values obtained by the CLOGP program. The log P TLC values of the investigated (E)-3-(X-benzylidene)-2,3-dihydro-1-benzopyran-4-ones (3) were compared with those of the previously investigated structurally related chalcones (1) and (E)-2-(X-benzylidene)-1-tetralones (2). It was found that the log P TLC values of the respective 4′-X-benzylidene analogues increased in the 1 < 3 < 2 order. The average difference between the log P TLC data of the respective cyclic 4′-X-benzylidene derivatives 2 and 3 was found to be 0.23 log P unit. The effect of the position (ortho, meta, or para) of the aromatic substituents did not follow regularity in either of the two series. The results indicate the importance of both steric and electronic factors in the lipophilicity of the investigated compounds.

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A simple and precise reversed-phase thin-layer chromatographic (RP TLC) method for simultaneous separation of fluoxetine and citalopram in pharmaceutical preparations has been developed and validated. Separation was performed on RP-18 F254 TLC plates with methanol-0.05 M phosphate buffer (pH 5)-triethylamine 68:27:5 (v/v) as mobile phase. Densitometric detection was performed at 230 nm. The method was validated for linearity, accuracy, precision, selectivity, and robustness. Calibration plots showed the response, as peak area, was a linear (r 2 > 0.9988) function of the amounts of the compounds in the concentration range 500–5000 ng per spot. Statistical analysis proved the method was both precise and accurate. The method was successfully used for analysis of citalopram and fluoxetine in their pharmaceutical preparations, with recovery of the compounds ranging from 99.10 to 101.70% of the labeled amount.

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M. Stefaniak, A. Pyka , and J. Śliwiok , Application of the R F values and topological indices to modify log P according to Rekker of selected porphyrins and metalloporphyrins separated by the RP-TLC technique, Planar Chromatography

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