Elżbieta Brzezińska

Cytotoxic effects, alkylating properties and molecular modelling of coumarin derivatives and their phosphonic analogues.

The cytotoxic effects and alkylating activity of a series of 3-[1-(alkylamino)-ethylidene]-chroman-2,4-dione (4a-4c), 2-methoxy-3-[1-(alkylamino)-ethylidene]-2,3-dihydro-2,4-dioxo-2lambda(5)-benzo[e][1,2] oxaphosphinane (5a-5c) and [2-oxo-4-phenyl(alkyl)-2H-chromen-3-yl]-phosphonic acids dimethyl ester (6a-6c) on the two leukemia cell lines HL-60 and NALM-6 have been determined. The test compounds are much more toxic to NALM-6 cells than to HL-60 cells. IC(50) data are up to nine times lower for the NALM-6 than for the HL-60 cell lines. As determined in an in vitro Preussmann test phosphonic derivatives 6a-6c possess very high (+++) alkylating activity, phosphoric derivatives 5a-5c are less active (++) while the derivatives 4a-4c can be included in the group of low activity (+) alkylating agents. Using regression analysis QSAR we found a relationship between biological activity and the physicochemical properties of the test compounds. Their cytotoxic effect increases with an increase of the hydrophobic parameters in the region of the substituents at the 2-, 3- and 4-positions of the benzopyrone skeleton of 4-6.

Normal and reversed phase thin layer chromatography data in quantitative structure-activity relationship study of compounds with affinity for serotonin (5-HT) receptors.

Quantitative structure-activity relationship (QSAR) analysis of 20 drugs with affinity for serotonin (5-HT) receptors was carried out. A set of physicochemical parameters calculated by HyperChem 7.0 and ACDLabs 8.0 programs and chromatographic data were applied in the analysis. Thin layer chromatography was performed on silica gel NP 60F(254) and silica gel RP2 60F(254) (silanized) plates impregnated with solutions of aspartic acid, serine, phenylalanine, tryptophan, tyrosine, asparagine, threonine and their mixtures (denoted as S1-S11 models), with two mobile phases - the systems were chosen as models of drug-5-HT-receptor interaction. Relationships between chromatographic data and molecular descriptors and biological activity data were found by means of regression analysis. The correlations obtained for the compounds with serotoninergic activity represent their interaction with the proposed biochromatographic models (S1-S11). The presented regression models based on biochromatographic studies can be an efficient tool in the QSAR analysis for initial prediction of compounds activity direction within 5-HT receptors.

Evaluation of the lipophilicity of selected sunscreens--a chemometric analysis of thin-layer chromatographic retention data.

The lipophilicities of 22 selected sunscreens, preservatives, and vitamins used in topical skin products were measured by thin-layer chromatography. Lipophilicity was calculated in silico from the sunscreen molecular structures and compared to the experimental octanol/water partition coefficients found in the literature. The retention of the compounds was investigated on an RP-18 stationary phase with mobile phases consisting of water and one of six organic modifiers (dioxane, tetrahydrofuran, acetone, acetonitrile, methanol, and dimethylformamide) at different concentrations. The theoretical lipophilicities were calculated by several computational algorithms and the results of these calculations were compared using cluster analysis. The results showed that two out of the six investigated organic modifiers (dioxane and acetone) may be used to estimate the octanol/water partition coefficients of highly lipophilic compounds having lipophilicities that cannot be measured directly by the shake-flask method.

Normal-phase TLC analysis of UV filters avobenzone and octocrylene in sunscreen preparations

TLC separation of the UV filters avobenzone (AVO) and octocrylene (OCR) on RP-18 and silica gel 60 as stationary phases, with numerous mobile phases, revealed that these compounds have similar retention properties under almost all the chromatographic conditions investigated. Analysis of avobenzone in the presence of octocrylene may be achieved on silica gel 60 with cyclohexane-diethyl ether 1:1 (v/v) as mobile phase, at the selective wavelength 380 nm, at which octocrylene does not absorb (Method A). Analysis of octocrylene in the presence of avobenzone by the same method was, however, impossible because of insufficient chromatographic separation of AVO and OCR and overlap of the absorption ranges of AVO and OCR (with OCR peaks being obscured by those of AVO). An alternative separation strategy was proposed that proved successful for OCR in the presence of AVO. This involved chromatography on silica gel 60 with cyclohexane-piperidine 15:1 (v/v) as mobile phase (Method B). When these chromatographic conditions were used, retention of avobenzone changed substantially and OCR peaks became clearly visible. Spectrodensitometric scanning for OCR was then performed at 300 nm. Both methods were validated, and gave calibration plots of good linearity.

NP TLC DATA IN STRUCTURE-ACTIVITY RELATIONSHIP STUDY OF SELECTED COMPOUNDS WITH ACTIVITY ON DOPAMINERGIC, SEROTONINERGIC, AND MUSCARINIC RECEPTORS

The available information on ligand-binding sites within the metabotropic receptors allows us to choose and apply chemical elements of the biological environment in the chromatographic analysis, which are responsible for formation of the drug-receptor complex. This information provides the opportunity to form analytical and statistical models of interactions between the drugs studied and dopaminergic, serotoninergic, and muscarinic receptors. Simple analytical models for predicting the direction of potential activity within these receptors with the use of chromatographic data and calculated physicochemical parameters were presented. The statistical tool used in this study was Stepwise Discriminant Analysis (SDA). The joint element of simulated environment interactions between various compounds and a biological goal is aspartic acid. The NP TLC plates, impregnated with a solution of aspartic acid (L-Asp), were used in two developing solvents as metabotropic receptors interaction models. The 33 selected drugs were divided into three groups of activity. The following group codes were assigned to them a priori: D, 5HT, and M (for compounds with activity on dopaminergic, serotoninergic, and muscarinic receptors, respectively). The presented discriminant models based on biochromatographic studies and physicochemical data are an efficient tool in the SAR analysis for initial prediction of compound activity direction within selected receptors.

Simultaneous NP TLC Analysis of the Sunscreens Diethylamino Hydroxybenzoyl Hexyl Benzoate and Octyl Methoxycinnamate

A simple, rapid, and effective method for TLC separation of two EU-authorized UV filters octyl methoxycinnamate (OMC) and diethylamino hydroxybenzoyl hexyl benzoate (DHHB) on silica gel 60 is proposed. Separation conditions were optimized and cyclohexane-diethyl ether-acetone 15:1:2 (v/v) was used as mobile phase. Quantification of both filters on the same chromatographic plates was achieved by densitometric scanning in absorption-reflectance mode at 300 and 360 nm, respectively. The method enabled separation of other UV-absorbing ingredients commonly found in cosmetic sunscreen preparations, for example parabens or ethylhexyltriazone (ET). Good quality, linear calibration plots were generated over the range 200–2000 ng per spot both for OMC and DHHB. The method was validated.

Quantification of Sunscreen Benzophenone-4 in Hair Shampoos by Hydrophilic Interactions Thin-Layer Chromatography/Densitometry or Derivative UV Spectrophotometry

Benzophenone-4 (BZ4) was separated from surfactants, dyes, preservatives, and other components of hair shampoos by thin-layer chromatography on silica gel 60 stationary phase, with ethyl acetate-ethanol-water-pH 6 phosphate buffer (15u2009:u20097u2009:u20095u2009:u20091u2009v/v/v/v) as mobile phase. Densitometry scanning of chromatograms was performed at 285u2009nm. The densitometric calibration curve for BZ4 was nonlinear (second-degree polynomial), with R > 0.999. The limits of detection and quantification were ca. 0.03 and ca. 0.1u2009μgu2009spot−1, respectively. The results obtained by HPTLC-densitometry were compared to those obtained by zero and 2nd derivative UV spectrophotometry. In the case of spectrophotometric methods, calibration curves were linear with R > 0.9998. The chromatographic method was fully validated.

RP-18 chromatographic-based study of the blood—brain barrier permeability of selected sunscreens and preservatives

Chemical ultraviolet (UV) filters and preservatives used currently in sunscreen preparations are compounds of diverse structures, and the safety of their application depends on their inability to penetrate the skin and other barriers present in the human body. However, at least some of these chemicals meet the general requirements of the good blood—brain barrier (BBB) permeability described in the literature sources. The objective of this study was to examine the behavior of selected cosmetic raw materials (UV filters and preservatives) towards the BBB on the basis of the BBB permeability models developed in our earlier study, based on easily accessible RP-18 thin-layer chromatographic data and calculated molecular descriptors. The computed BBB permeability parameters B1 and B2 correlate with the chromatographic data (RF, RF/PSA) and calculated physicochemical descriptors usually associated with the BBB permeation (HA, Sa, DM, log D). The relationships between these values were developed by stepwise multiple regression analysis, validated, and found to explain 93–96% of the total variance. The models of the BBB permeation based on classification functions obtained previously from discriminant function analysis were used to assign the studied compounds to the groups of good (CNS+) or poor (CNS−) blood—brain barrier permeability, suggesting the inability of the majority of these compounds to cross the BBB. The universal character of BBB permeability models developed earlier was confirmed.

SPE/TLC/Densitometric Quantification of Selected Synthetic Food Dyes in Liquid Foodstuffs and Pharmaceutical Preparations

Selected synthetic food dyes (tartrazine, Ponceau 4R, Brilliant Blue, orange yellow, and azorubine) were isolated from liquid preparations (mouthwashes and beverages) by Solid Phase Extraction on aminopropyl-bonded silica with diluted aqueous sodium hydroxide as an eluent. The extraction step was followed by thin layer chromatography on silica gel 60 with chloroform-isopropanol-25% aq. ammonia 1u2009:u20093u2009:u20091 (v/v/v) as mobile phase and the densitometric quantification of dyes was achieved using quadratic calibration plots (R2 > 0.997; LOQ = 0.04–0.09u2009μgspot−1). The overall recoveries for all studied dyes were at the average level of over 90% and the repeatability of the proposed procedure (CV ≤ 4.1%) was sufficient to recommend it for the routine quantification of the aforementioned dyes in liquid matrices.

Application of RP-18 thin-layer chromatography and quantitative structure–activity relationship analysis for the prediction of the blood–brain barrier permeation

In this study, a number of computed or chromatographically measured (RP-18 thin-layer chromatography [TLC]) descriptors are presented. The relationships between these descriptors and the observed (BBobs) and calculated (B2) BBB bioavailability were studied by stepwise multiple regression analysis and discriminant function analysis on a group of 34 compounds of diverse structures. Useful models of the blood–brain distribution given by the equations: BBobs = −1.19 + 2.05 B2 + 3.89 RF − 62.31 RF/PSA + 0.290 log D (R2 = 0.85, n = 24) and B2 = 4.06 − 1.61 HA − 1.95 HD + 105.49 RF/PSA (R2 = 0.95, n = 34) were developed and validated. Models for discrimination between CNS+ and CNS− compounds were built on the basis of RF, RF/PSA, HD, and B2 descriptors. The diagnostic power of important parameters was evaluated by cluster analysis. Thirty-four compounds examined throughout this study were successfully assigned to two clusters: CNS+ and CNS−. Analysis of variances for 6 descriptors (HD, HA, RF, RF/PSA, DM, and B2) confirmed the conclusion that the parameters of good differentiating power are B2, HA, HD, RF/PSA ,and RF. The results of the chromatographic analysis proposed in this study (RP-18 TLC) are a source of valuable information on the ability of compounds to cross the BBB. This simple, inexpensive, and very rapid chromatographic technique may be used to assess the BBB permeability of compounds isolated or synthetized on a very small scale. The computed B2 descriptor is a convenient and readily available parameter useful also in the case of theoretical structures.