HPTLC chromatography of androstene derivates. Application of normal phase thin-layer chromatographic retention data in QSAR studies

The chromatographic behavior of seven 16-oximino derivatives of 3beta-hydropxy-5-androstene have been investigated using the normal-phase (NP) HPTLC chromatographic mode of the type silica-non-polar diluent (benzene)-polar modifier (acetonitrile, ethyl acetate, or dioxane). The linear relationship between the retention constants (R(M)) and the logarithm of the organic modifier content in the mobile phase allowed for the calculation of R(M)0 values. The influence of substituent in the molecule on extrapolated retention data is discussed. To better understand the retention mechanism in the separation of androstene compounds, the functional group contributions (tauX) were compared with Hansch substituent constants (pi). An attempt to quantitate the lipophilicity of the investigated compounds using normal phase thin-layer chromatographic R(M)0 value was made. Also, the relative lipophilicity values determined previously by RPC as well as activity were compared with NPC data.     

Determination of clofibrate in biological fluids by thin-layer and gas-liquid chromatography

A specific and sensitive method is described for the detection of clofibrate in biological fluids. The drug is separated from associated fatty acids by thin-layer chromatography and the methyl ester is quantified by gas-liquid chromatography. Recovery is excellent, and any small losses are corrected with an internal recovery standard. Although more time-consuming than other available techniques, the method offers advantages for accurate studies of clofibrate metabolism.     

Quantitation of chlordiazepoxide and its metabolites in biological fluids by thin-layer chromatography

Chlordiazepoxide and its 4 major metabolites were assayed after separation by thin-layer chromatography following extraction from biological fluids. The compounds become intensely fluorescent in the presence of red, fuming nitric acid. The resulting compounds are quantitated with a spectrodensitometer with a fluorescent attachment. The sensitivity varies between 0.05 and 0.1 μg. The coefficient of variation is 1.4% for assays in urine and 6.4% in serum.     

Insulin's structural behavior and its relation to activity

This paper discusses the hypothesis that insulin undergoes a conformational change either before or during its binding to the receptor. The evidence for this is not conclusive but allows us to reconcile the following observations: (1) no chemical modification or deletion of invariant surface residues has abolished the hormone's activity—only reduced its potency. (2) Reduction in potency follows many modifications to different side chains, both variant and invariant. (3) There are insulins with perfectly preserved structure (by the criteria of aggregation, spectroscopy, and x-ray analysis) that have markedly reduced potency. (4) Insulins with disturbed structure still exhibit real, sometimes substantial activity.     

Quantitative high-performance thin-layer chromatography determination of common liposome components and critical parameters influencing the analysis results

The aim of this study was to investigate the performance of a newly devised high-performance thin-layer chromatography (HPTLC) method in quantifying common liposome membrane components, including the five phospholipids (PLs), phosphatidylcholine, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol, as well as cholesterol, cholesteryl hemisuccinate, and linoleic acid. Besides strictly keeping to a standardized procedure, three parameters were particularly critical for proper quantification. First, a relative humidity of higher than 60% caused migration distances to increase and reduced the resolution of the PLs on a silica-gel 60 HPTLC plate. Second, PLs underwent oxidative combustion during storage for 2 or 24 hours on an HPTLC plate, with peak losses of up to 25–44%. These losses could be prevented by storage under nitrogen and, to some extent, by the addition of the antioxidant, DL-α-tocopherol. Third, even with automated sample application, the accuracy and consistency of the application volume proved to be an important cause of error and needs routine verification. Considering these parameters, the method was found to accurately and precisely determine the composition of three different liposome preparations. The recovery was 97.2–101.8%, compared to secondary methods, and consistent over different days and with different operators (mean RSD of the recovery: 2.03?±?1.16%, n?=?9). The working range was determined to be 100–300?ng in the case of the PLs (individual limit of determination between 40 and 80?ng) and 20–60?ng in the case of cholesterol (limit of determination: 16?ng).     

Chemometric analysis of Hymenoptera toxins and defensins: A model for predicting the biological activity of novel peptides from venoms and hemolymph

When searching for prospective novel peptides, it is difficult to determine the biological activity of a peptide based only on its sequence. The “trial and error” approach is generally laborious, expensive and time consuming due to the large number of different experimental setups required to cover a reasonable number of biological assays. To simulate a virtual model for Hymenoptera insects, 166 peptides were selected from the venoms and hemolymphs of wasps, bees and ants and applied to a mathematical model of multivariate analysis, with nine different chemometric components: GRAVY, aliphaticity index, number of disulfide bonds, total residues, net charge, pI value, Boman index, percentage of alpha helix, and flexibility prediction. Principal component analysis (PCA) with non-linear iterative projections by alternating least-squares (NIPALS) algorithm was performed, without including any information about the biological activity of the peptides. This analysis permitted the grouping of peptides in a way that strongly correlated to the biological function of the peptides. Six different groupings were observed, which seemed to correspond to the following groups: chemotactic peptides, mastoparans, tachykinins, kinins, antibiotic peptides, and a group of long peptides with one or two disulfide bonds and with biological activities that are not yet clearly defined. The partial overlap between the mastoparans group and the chemotactic peptides, tachykinins, kinins and antibiotic peptides in the PCA score plot may be used to explain the frequent reports in the literature about the multifunctionality of some of these peptides. The mathematical model used in the present investigation can be used to predict the biological activities of novel peptides in this system, and it may also be easily applied to other biological systems.     

neo-Clerodane diterpenoids from Ajuga: structural elucidation and biological activity

The presence of several types of allelochemicals has been reported from Ajuga, a Labiatae genus comprising more than 40 species of wide distribution in extratropical regions of both hemispheres. The genus is of great medicinal and economic importance and among the biological properties of the secondary metabolites, the antifeedant activity against pest insects appears to be related to the presence of neo-clerodane type diterpenes. This review focuses on the isolation and structural elucidation of this type of compounds from Ajuga species and the hemisynthetic compounds of closely related structure obtained. The reported biological activity of crude extracts and isolated diterpenes will be briefly commented.

Carrageenans from chilean samples of Stenogramme interrupta (Phyllophoraceae): structural analysis and biological activity

Carrageenans extracted from cystocarpic and tetrasporic Stenogramme interrupta were analysed by chemical and spectroscopic methods. The carrageenan from cystocarpic plants is composed predominantly of 0.5 M KCl-insoluble and 1 M KCl-soluble fractions. The insoluble fraction contained iota-carrageenan as the major component with alpha-carrageenan and pyruvated carrageenan as minor components. The soluble fraction is highly heterogeneous and did not contain the precursors mu- and nu-carrageenans. The polysaccharide from tetrasporic plants is composed of zeta- and lambda-carrageenans, and low sulfated galactans. It is soluble in KCl and partly cyclized by alkaline treatment. The antiviral and anticoagulant properties of the insoluble polysaccharide fraction from cystocarpic S. interrupta and the polysaccharide from tetrasporic S. interrupta are reported the results of which suggest promising antiherpetic activity.     

Rapid biological and chemical analyses of bacterial endotoxins separated by preparative thin-layer chromatography

Methods have been elaborated for rapid location of biologically active bacterial endotoxin components on preparative thin-layer chromatography (tlc) by Limulus lysate clotting assay. The separation of the components from silicic acid is not necessary. Further assays were established for the semiquantitative estimation of endotoxic activites (Shwartzman reactivity, chick embryo lethality, and non-specific tumor resistance enhancement) without complete removal of silicic acid.Quantitative chemical analytical procedures were also elaborated to determine the molar ratios of the biologically active components separated and detected in the above tlc system. These included phosphorus, hexosamine, heptose, 2-keto-3-deoxyoctonate, and long-chain carboxylic acid content measurements. Here again, the chemical determinations were carried out in the presence of silicic acid.     

Simultaneous separation of lysophospholipids from the total lipid fraction of crude biological samples using two-dimensional thin-layer chromatography

A novel solvent system for two-dimensional thin-layer chromatography was shown to simultaneously separate lysophospholipid standards, including lysophosphatidylcholine, lysophosphatidylethanolamine, lysophosphatidylserine, lysophosphatidylinositol, lysophosphatidylglycerol, lysophosphatidic acid, lysosphingomyelin (sphingosylphosphorylcholine), and sphingosine-1-phosphate from diradylphospholipids, glycosphingolipids, and neutral lipids. Lysophospholipids contained in the total lipid fraction of activated platelets were also well separated by the same system. The present system is a useful tool for the metabolic and structural analysis of lysophospholipids in biological samples.     

Chemometric discrimination between streams based on chemical, limnological and biological data taken from freshwater fishes and their interrelationships

The VALIMAR project aims at identifyingbiomarkers in fish that are suitable to detectand predict environmental stress from chemicalpollution or from limnological parameters inthe field. For two small streams in SouthernGermany, concentration values of 31contaminants in water and sediment and 12 limnological parameters as well as 27 biomarkersmeasured in brown trout and stone loach werecollected. All these physicochemical andbiological parameters have been analysed forpatterns that discriminate between the streams,using discriminant analysis (DA), analysis ofvariance (ANOVA) and of covariance (ANCOVA), and principal component analysis (PCA) asmultivariate statistical techniques. Moreover,the biological data were analyzed with respectto species-specific patterns, and the partialleast-squares regression method (PLS) was usedto study the impact of chemical and limnological data on the health status of the targetspecies as characterized by the biomarker data.Abiotic as well as biotic data yielded goodseparations between the streams, with theultrastructure of gill (US-gill) being thestrongest discriminator variable among all 27biomarkers tested. With regard to the two fishspecies, the biomarker data from brown troutshow significantly greater differences betweenthe two streams than the biological responsesin stone loach. Application of PLS yieldssignificant regression models for only fewbiomarkers including US-Gill, which can bepartly traced back to significant noise levelsin the data set as quantified by permutationtests.     

Determination of peptidylglycine alpha-amidating monooxygenase activity in human serum by thin-layer chromatography

We developed a simple assay system for the quantitative evaluation of peptidylglycine alpha-amidating monooxygenase activity using as substrate a 125I-labeled synthetic tripeptide, 125I-D-Tyr-Val-Gly, thin-layer chromatography, and a radiochromatoscanner. The basic principle of this method is that thin-layer chromatography separates the reaction product, 125I-D-Tyr-Val-NH2, from the substrate in an assay mixture. The 125I activities of both substrate and product separated from each other on a thin-layer chromatography plate were quantified with a radiochromatoscanner and the rate of conversion of the substrate to the product was calculated from their counts. Human serum was used as an enzyme source and the values of alpha-amidation activity obtained by our method under optimal conditions were almost identical to those of the published method using ion-exchange chromatography (sulphopropyl-Sephadex C-50 column) and a gamma-counter. Our method makes it possible to estimate the 10-pmol level of the product using 10 microliters of human serum and to assay a large number of samples rapidly and easily. It is therefore thought to be very useful for screening various tissues for alpha-amidation activity.