[Interconversion of stereochemically unstable chiral drugs. Part III: Using beta-cyclodextrin as a chiral stationary phase for HPLC separation of diazepam conformers coupled with an off-line NMR experiment]. / Interkonverzia stereochemicky nestálych chirálnych lieciv. Cast III: Separácia konformérov diazepamu HPLC metodou pouzitim beta-cyklodextrínu ako chirálnej stacionárnej fázy v off-line spojení s NMR experimentom.

Chiral beta-cyclodextrin was used to separate diazepam conformers. Several mobile phases of the composition acetonitrile/acetate buffer 200 mmol/l (pH=3.3, 5.5, 6.5) were employed for this purpose. As follows, the influence of addition of chiral beta-cyclodextrin to the mobile phase on diazepam separation was studied. The interconversion was a concurrence process of separation, resulting from stereolability of the diazepam molecule. The influences of temperature, flow rate, pH, and ionic strength of the mobile phase on interconversion and chromatographic parameters (retention factor and selectivity coefficient) were studied. Complementary off-line NMR measurements were carried out with the goal to confirm the structure of diazepam in the presence of an acid mobile phase.

[Interconversion of stereochemically unstable chiral drugs: utilization of chromatographic techniques for the study of enantiomerization. Part II: practical applications]. / Interkonverzia stereochemicky nestálych chirálnych lieciv-- vyuzitie chromatografických techník na stúdium enantiomerizácie cast II: praktické aplikácie.

Enantiomerization is a first-order reaction; it means interconversion of one enantiomer into another (and vice versa). This phenomenon is a typical feature of some configurationally unstable chiral compounds and it complicates separation of racemic mixtures. For the study of enantiomerization, chromatographic separation techniques (GC, SFC, CE, MEKC, HPLC) and NMR can be used. Chromatographic methods suitable for investigation of enantiomerization include dynamic chromatography (if time scales of enantiomerization and separation are the same) and stopped-flow chromatography (time scales of both processes are different). The present paper surveys the research of enantiomerization from 1975, when papers describing enantiomerization in greater detail were published, to the present. Today, mathematical approaches and computer-assisted deconvolution procedures are commonly used for evaluation of enantiomerization--calculation of thermodynamic parameters (deltaGapp, deltaHapp, deltaSapp) and rate constants (klapp, k(-1)app). The aim of many publications was not only determination of the enantiomerization energy barrier, but the influence of the chiral stationary phase on enantiomerization was studied as well. In some cases, enantiomerization was used for preparative purposes--a pure enantiomer was obtained and thus complicated synthesis was excluded.

[Interconversion of stereochemically unstable chiral drugs: utilization of chromatographic techniques for the study of enantiomerization, calculation of thermodynamic parameters. Part I: theoretical aspects]. / Interkonverzia stereochemicky nestálych chirálnych lieciv-- vyuzitie chromatografických techník na stúdium enantiomerizácie, výpocet termodynamických parametrov. Cast I.--teoretické aspekty.

The paper explains the theoretical aspects of the process of enantiomerization and describes its characteristic features (generation of a plateau). In addition, some complications are presented that are produced by enantiomerization either from analytical or pharmacological points of view. It also defines the way of how to calculate energy barriers of enantiomerization according to the methods used for the separation of racemic mixtures (stopped-flow or dynamic chromatography). Mathematic models useful in deconvolution of chromatograms are also described. With the use of dynamic methods it is not possible to quantitatively evaluate the obtained chtromatograms and calculate thermodynamic parameters without computer-assisted deconvolution.

[A study of physicochemical properties of 2-, 3-, 4-alkoxyphenylcarbamic acid derivatives with a substituted N-phenylpiperazine moiety in the basic part]. / Stúdium fyzikálno-chemických vlastností derivátov kyseliny 2-, 3-, 4-alkoxyfenylkarbámovej s bázickou castou tvorenou substituovaným N-fenylpiperazínom.

The paper presents the study of some physicochemical properties of 2-, 3-, 4-alkoxyphenylcarbamic acid derivatives with various substituted N-phenylpiperazin-1-yl moiety in the basic part of the molecule. Elemental analysis, melting point, solubility, surface activity, dissociation constant and some lipophilicity parameters i.e.--partition coefficient, capacity factor obtained from HPLC, and R(M) values from reversed-phase thin-layer chromatography were determined.