Determination of the Lipophilicity of Xanthines by Reversed-Phase Liquid Chromatography

JPC – Journal of Planar Chromatography – Modern TLC -     

Enantiomeric separation of new phytoalexin analogs with cyclofructan chiral stationary phases in normal‐phase mode

For the first time, three different derivatized cyclofructan chiral stationary phases were used for the direct high‐performance liquid chromatographic enantiomeric separation of 11 new racemic analogs of a natural indole phytoalexin. This class of compounds is known to have significant antiproliferative activity and other potentially useful pharmacological properties. The effect of various experimental factors was investigated to optimize the separations in the normal‐phase mode. It was found that the nature of polar modifier and additive in the mobile phase have significant impact on the enantioseparations. Better chiral recognition of analyzed compounds was achieved on (R)‐naphthylethyl carbamate cyclofructan 6 than on isopropyl carbamate cyclofructan 6 and dimethylphenyl carbamate cyclofructan 7. The thermodynamic parameters showed that the chiral separation was enthalpy controlled in all cases.     

HPLC Enantioseparation of Novel Spirobrassinin Analogs on the Cyclofructan Chiral Stationary Phases

A novel series of nine chiral analogs of spirobrassinin, which have potential biological activity, was separated for the first time on three different derivatized cyclofructan chiral stationary phases in the normal phase mode. The effects of mobile phase composition, the type and concentration of polar modifier, additives, and the analyte structure on the retention and enantioseparation were studied. The results proved that for cyclofructan-based chiral stationary phases, the R-naphthylethyl carbamate cyclofructan 6 provides the best separation efficiency for the analyzed compounds. The effect of temperature on the separation was also investigated and the corresponding thermodynamic parameters were evaluated from linear Van’t Hoff plots (lnk or lnα versus 1/T). It was found that the enantioseparation was enthalpy controlled. In addition, the elution order of the enantiomers was determined in all the cases.     

Kinetic study of the thermally initiated cyclocondensation of some 1,3-dimethyl-4-alkylamino-5-nitrosouracils

The isothermal and non-isothermal DSC method was used to investigate the influence of changes in structure of 1,3-dimethyl-4-alkylamino-5-nitrosouracils on the 8-substituted theophyllines originating in the cyclocondensation reaction. The evaluation of the optimum reaction mechanism obtained on the basis of the corresponding model functions by using the integral method of Coats and Redfern is discussed. Significant differences, depending on the nature of the substituents, were observed in the course of the reaction.

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Zusammenfassung Der Einflu\ von VerÄnderungen in der Struktur von 1,3-Dimethyl-4-alkylamino-5-nitrosouracilen auf die in einer Zyklokondensationsreaktion gebildeten, 8-substituierten Theophylline wurde mittels isothermer und nicht-isothermer DSC untersucht. Die optimalen, basierend auf entsprechenden Modellfunktionen bei Anwendung der Integralmethode von Coats und Redfern erhaltenen Reaktionsmechanismen werden diskutiert. Im Verlaufe der Reaktion wurden signifikante, von der Natur der Substituenten abhÄngende Unterschiede festgestellt.

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1,3--4--5- 8- , . , , - . .

     

RP TLC Analysis of New Antidepressants in Pharmaceutical Preparations

JPC – Journal of Planar Chromatography – Modern TLC - A simple and precise reversed-phase thin-layer chromatographic (RP TLC) method for simultaneous separation of fluoxetine and...     

Enantioseparation of Novel Amino Analogs of Indole Phytoalexins on Macrocyclic Glycopeptide-Based Chiral Stationary Phase

Direct chiral separation of the enantiomers of spirobrassinin, 1-methoxyspirobrassinin and ten novel cis- and trans-diastereoisomers of 2-amino analogs of indole phytoalexin 1-methoxyspirobrassinol methyl ether on macrocyclic glycopeptide-based chiral stationary phase (CSP) with teicoplanin (Chirobiotic T) was studied. Normal phase eluents containing n-hexane with modifiers ethanol and 2-propanol were used. The effects of mobile phase composition, structure of the analytes and temperature were investigated. Chiral resolution on teicoplanin CSP was achieved only in the case of trans-diastereoisomers. The van??t Hoff plots were found to show linear behavior in all cases. It was found that studied normal phase enantioseparations were enthalpy driven. The elution order of the enantiomers was determined in some cases.     

Thermal behaviour of 1,3-dimethyl-4-alkylamino-5-nitrosouracils

The thermally initiated cyclocondensation of 1,3-dimethyl-4-alkylamino-5-nitrosouracils (I), giving rise to the 8-substituted theophyllines (II), was studied by DSC. The corresponding reaction enthalpies were determined for six derivatives of I.     

Preliminary TLC Analysis of Fructooligosaccharides as Feed Additives

JPC – Journal of Planar Chromatography – Modern TLC - A rapid, simple qualitative thin-layer chromatographic method has been developed for separation of mono- and fructooligosaccharides...     

Thermoanalytical study of cyclization reaction of some thioureates

Thermal initiated conversion of N-aryl-N'-(2-benzylpyridinium)thioureates into 2-arylamino-4H-benzo[d][1,3]thiazines was studied by non-isothermal differential scanning calorimetry (DSC), thermogravimetry (TG) and differential thermal analysis (DTA) in the solid-state. The values of molar reaction ethalpies (DH _r) of six derivatives of thioureates and the melting parameters (T _f, DH _f, DS _f) of the obtained products - benzothiazines were determined by the DSC method. This revised version was published online in August 2006 with corrections to the Cover Date.