András Gergely

Utility of cyclodextrins in the formulation of genistein. Part 1. Preparation and physicochemical properties of genistein complexes with native cyclodextrins

Isoflavones are suitable guest molecules for inclusion complex formation with cyclodextrins (CDs). The molecular encapsulation with CDs results in a solid, molecularly dispersed form and in a significantly improved aqueous solubility of isoflavones. Genistein, a key isoflavone constituent of Ononidis spinosae radix was found to form a supramolecular, non-covalent inclusion complex with both beta-cyclodextrin (beta-CD) and gamma-cyclodextrin (gamma-CD), while it did not form a stable complex with alpha-CD. The guest genistein was found to spatially located in the less polar cavity of cyclodextrin. The isolated binary genistein/CD complexes appeared novel crystalline lattices. The in vitro dissolution of genistein entrapped into both beta- and gamma-CD, significantly surpassed that of the plain isoflavone.

A review of the application of chiroptical methods to analytical chemistry.

The analytical applications of the two most important chiroptical methods, optical rotatory dispersions (ORD) and circular dichroism (CD), have been surveyed, emphasizing the methods corresponding to the profile of the Journal of Pharmaceutical and Biomedical Analysis. After a brief introduction of the ORD and CD methods, the advantages and drawbacks of the application of the two methods have been described, and compared, and the calibration of ORD and CD instruments have been given. The analytical applications have been divided as follows: the use of ORD and CD in identification studies, the direct determination of optically active substances, the determination of optically active compounds after chromophore group formation, determination of optically inactive substances via their products with optically active compounds. The difference chiroptical methods increasing the selectivity of measurements and the chiroptical titrations have been summarized. Stress has been laid on the applicability of selective chiroptical detectors (based on laser light, too) used in liquid chromatography and the future developments have been mentioned.

Determination of enantiomeric purity by simultaneous dual circular dichroism and ultraviolet spectroscopy.

A method is described for the determination of enantiomeric composition. The ellipticity and absorbance of the sample are measured simultaneously by CD and UV spectroscopies, and the resulting G value is determined. G is an intensive physico-chemical parameter, a close derivative of anisotropy factor. Its magnitude is identical with opposite sign for enantiomers. The experimental G value is concentration-independent, as long as both absorption and ellipticity are linear functions of concentration. The analytical procedure introduced here is simple, rapid, and inexpensive, even though it includes calibration with standards of established enantiomeric composition. Provided the sample contains some UV-active contaminant(s), the method can be used after achiral chromatographic purification. By virtue, the method lacks several sources of error, arising normally from concentration inaccuracies. Applicability of the principles is tested by the example of phenylglycine and mandelic acid. Advantages of the method allowed the determination of phenylglycine enantiomer purity with an accuracy of 0.1%.

Characterization of lactate–guanidinium and lactate–lactate interactions in aqueous solution by spectropolarimetry

Spectropolarimetry has been used to quantify the lactate–guanidinium and lactate–lactate equilibrium interactions in aqueous solution. Association constants for the lactate–guanidinium and lactate–lactate formations are 6.11 dm3 mol–1 and 1.12 dm3 mol–1, respectively, in aqueous solution; 6.11 dm3 mol–1 is a high value for an electrostatic interaction in water. This stability, however, cannot account for the extremely strong lactate–protein binding, observed earlier by NMR spectroscopy. The molar rotation coefficients for both the heteroassociation and homoassociation complexes are also calculated.The homoassociative lactate–lactate binding is the first such interaction, whose constant has been determined by spectropolarimetry in aqueous solution.

Three new steroids from the roots of Serratula wolffii

Investigation of the methanol extract of the roots of Serratula wolffii resulted in an ecdysone-related compound, 2beta,3beta,20R,22R,25-pentahydroxy-5beta-cholest-6,8(14)-dien (1), a new ecdysteroid, 24-methylene-shidasterone (2), the known compound stachysterone B (3) and its 14,15-alpha-epoxide (4), a novel natural product. The structures of compounds 1-4 were established by spectral analysis ((1)H NMR, (13)C NMR, COSY, NOESY, HMQC, HMQC-TOCSY and HMBC).

Stereochemical Study of Tolperisone, a Muscle Relaxant Agent, by Circular Dichroism and Ultraviolet Spectroscopy

The stereochemistry of tolperisone, a chiral aryl-alkyl basic ketone was investigated by means of circular dichroism (CD) and ultraviolet (UV) spectroscopy. The unusually high optical activity of tolperisone hydrochloride in the n-->pi* region is interpreted by the presence of a chiral conformer in solution. For stereochemical reasons, the C = O group and the aromatic moiety lack coplanarity by forming an inherently dissymetric chromophore, of M helicity. Similar helicity prevails in the crystal phase, according to the solid-state CD spectrum of (-)-tolperisone HCl salt. The chirality rule proposed by Snatzke for nonplanar benzoyl chromophores predicts the absolute configuration of (-)-tolperisone hydrochloride to be R, in agreement with other alpha-methyl-beta-amino-ketones.

Chapter 9 The use of circular dichroism as a liquid chromatographic detecto.

Abstract The article is a brief review of the applications of CD as a detector in both preparative and analytical liquid chromatography. The objectives are to identify elution orders for enantiomers, to measure enantiomeric purities and enantiomeric excesses, to analytically determine diastereoisomers, and to selectively determine chiral analytes when present as components in mixtures with achiral substances. For specific details on the instrumental arrangements for LC detection, readers are referred to the chapter by Bobbitt.

Enantiomer separation of imidazo-quinazoline-dione derivatives on quinine carbamate-based chiral stationary phase in normal phase mode.

The normal phase mode liquid chromatographic enantiomer separation capability of a quinine tert-butyl-carbamate-type chiral stationary phase (CSP) has been investigated for a set of polar [1,5-b]-quinazoline-1,5-dione derivatives. This class of chiral heterocycles is currently under development as potential alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) and/or N-methyl-D-aspartic acid (NMDA) receptor antagonists. The effect of the nature and concentration of polar modifier, i.e., ethanol and isopropanol, in n-hexane-based mobile phases, as well as the substituent pattern of the phenyl ring attached to the quinazolone framework on retention factor, enantioselectivity, and resolution was investigated. The Soczewiński competitive adsorption model was used to describe the relationship between the retention and the binary mobile phase compositions. According to this model, linear plots of the logarithms of retention factor versus molar fractions of the polar modifiers were obtained over a wide concentration range (X(B) between 0.15 and 0.35). Addition of equimolar ethanol yields higher resolution than isopropanol, R(S) values ranging between 1.54 and 2.75, whereas the latter allows to achieve moderately increased enatioselectivity. The resolution was further improved by using a ternary mixture of n-hexane:methanol:isopropanol/85:5:10 (v/v). The most pronounced selectivity factor alpha and resolution R(S) values were obtained for the para-hydroxy substituted compound, indicating that chiral recognition is sensitive to steric and stereoelectronic factors. In the course of optimization, the temperature-dependence on the chiral separation was also investigated. It turned out that the enantiomer separation is predominantly enthalpically driven in normal phase mode.

SEPARATION AND IDENTIFICATION OF TOFISOPAM STEREOISOMERS BY HYPHENATED HPLC-CD TECHNIQUE

The published method allows the separation of the four isomers of the anxiolytic 2,3-diazepine derivative, tofisopam. Assignment for the peaks of the two central and two helical isomers is performed by using the chromatogram of the pure tofisopam enantiomers and also considering the conformer-equilibrium was suggested by previous authors. The detection has been made by CD. The in situ CD spectra of the peaks, obtained by stop-flow method, definitely show different chiral character.

Determination of Circular Dichroism and Ultraviolet Spectral Parameters of Norgestimate- and Other Delta4-3-Ketosteroid Oxime Isomers Via Normal Phase HPLC Method

The oxime formation reaction of therapeutical progestogen (levonorgestrel, levonorgestrel acetate, norethisterone), androgen (methyltestosterone, testosterone phenylpropionate) and anabolic (nortestosterone phenylpropionate) Delta(4)-3-ketosteroids has been investigated. The ketosteroid-hydroxylamine reaction was monitored by reversed phase HPLC system. It was established, that under the experimental conditions applied the oxime formation was complete within 2 h. The reaction leads to the formation of Z and E oxime isomers. The isomers of norgestimate (levonorgestrel 17-acetate oxime) and other Delta(4)-3-ketosteroid oximes have been separated by a new normal phase HPLC method. The identification (elution order assignation) and determination of the formation ratio of the isomers have been performed by 1H NMR spectroscopy on the basis of the chemical shift differences of 4-H signals. The on-line CD and UV spectra of the pure oxime isomers were recorded and then molar ellipticities and absorbances of the isomers were calculated in the wavelength range of 200-300 nm via parameter estimation method.