Enantioselective analysis of fluoxetine in pharmaceutical formulations by capillary zone electrophoresis

Fluoxetine is an antidepressant, a selective serotonin reuptake inhibitor (SSRI) used primarily in the treatment of major depression, panic disorder and obsessive compulsive disorder. Chiral separation of racemic fluoxetine is necessary due to its enantioselective metabolism. In order to develop a suitable method for chiral separation of fluoxetine, cyclodextrin (CD) modified capillary electrophoresis (CE) was employed. A large number of native and derivatized, neutral and ionized CD derivatives were screened to find the optimal chiral selector. As a result of this process, heptakis(2,3,6-tri-O-methyl)-β-CD (TRIMEB) was selected for enantiomeric discrimination. A factorial analysis study was performed by orthogonal experimental design in which several factors are varied at the same time to optimize the separation method. The optimized method (50 mM phosphate buffer, pH = 5.0, 10 mM TRIMEB, 15 °C, + 20 kV, 50 mbar/1 s, detection at 230 nm) was successful for baseline separation of fluoxetine enantiomers within 5 min. Our method was validated according to ICH guidelines and proved to be sensitive, linear, accurate and precise for the chiral separation of fluoxetine.

Cyclodextrine screening for the chiral separation of amlodipine enantiomers by capillary electrophoresis

PURPOSE

Amlodipine is a long acting, dihydropyridine type calcium channel blocker frequently used in the treatment of hypertension and coronary insufficiency. The calcium channel blocking activity resides primarily in the S-amlodipine enantiomer, while R-amlodipine is a potent inhibitor of smooth muscle cell migration.

METHODS

In this study capillary electrophoresis was applied for the enantiomeric separation of amlodipine using different native and derivatized; neutral and charged cyclodextrines as chiral selectors. The effects of pH and composition of the background electrolyte, concentration and type of chiral selector, capillary temperature, running voltage and injection parameters have been investigated.

RESULTS

Stereoselective interactions were observed when using α-CD, β-CD, HP-β-CD, RAMEB, CM-β-CD and SBE-β-CD. Optimized separation conditions consisted on a 50 mM phosphate buffer, pH - 3.0, 20 mM RAMEB as chiral selector, + 25 kV applied voltage, 15°C temperature and UV detection at 238 nm. Using the optimized electrophoretic conditions we succeeded the chiral separation of amlodipine enantiomers in approximately 6 minute, the order of migration being R-amlodipine followed by S-amlodipine. The method was successfully applied for the determination of amlodipine enantiomers from commercially available pharmaceuticals. The linearity range, limits of detection and quantification, precision and accuracy were determined and the results obtained confirmed that the method was suitable for this purpose.

CONCLUSION

It can be concluded that the proposed capillary electrophoresis methods can be useful for routine pharmaceutical applications with benefits of its effectivity, simplicity, short analysis time and low consumption of analytes, solvents and chiral selectors.

Cyclodextrine screening for the chiral separation of carvedilol by capillary electrophoresis

Carvedilol is administered as a racemic mixture of the R(+)- and S(-)-enantiomers, although it was demonstrated that the two enantiomers exhibit different pharmacological effects and stereoselective pharmacokinetics. The aim of this study was the evaluation of several native and derivatized cyclodextrines as chiral selectors for the separation of carvedilol enantiomers. Stereoselective interactions were observed with four cyclodextrines (β-CD, hydroxypropyl-β-CD, randomly methylated β-CD and sulfobuthyl ether- β-CD). The effects of CD concentration, pH value and composition of the background electrolyte, capillary temperature, running voltage and injection parameters have been investigated. The method was validated for precision of peak-area response, linearity range and limits of detection and quantification. An efficient stereoselective capillary zone electrophoretic method was developed for the determination of carvedilol enantiomers using a simple 25 mM phosphate buffer at a pH = 2.5 and 10 mM β-CD as chiral selector, resulting in baseline separation of the two enantiomers with sharp peaks and relatively short analysis time. Highly satisfactory results were obtained from the analysis of carvedilol from tablets, indicating that the method is suitable for routine analysis of carvedilol in pharmaceutical products.

Chiral separation of indapamide enantiomers by capillary electrophoresis

PURPOSE

Indapamide is probably the most frequently prescribed diuretic drug, generally being used for the treatment of hypertension. It contains a chiral center in its molecule; is marketed as a racemic mixture; but there are rather few studies regarding the pharmacokinetic and the pharmacological effect differences of the two enantiomers. Our aim was the development of a simple, rapid and precise analytical procedure for the chiral separation of indapamide enantiomers.

METHODS

In this study capillary zone electrophoresis was used for the enantiomeric separation of indapamide using a systematic screening approach involving different native and derivatized; neutral and charged cyclodextrines as chiral selectors. The effects of pH value and composition of the background electrolyte, capillary temperature, running voltage and injection parameters have been investigated.

RESULTS

After preliminary analysis a charged derivatized CD, sulfobuthyl ether- β-CD, proved to be the optimum chiral selector for the enantioseparation. Using a buffer solution containing 25 mM disodium hydrogenophosphate - 25 mM sodium didydrogenophosphate and 5 mM sulfobuthyl ether- β-CD as chiral selector at a pH - 7, a voltage of + 25 kV, temperature 15°C and UV detection at 242 nm, we succeeded in the separation of the two enantiomers in approximately 6 minutes, with a resolution of 4.30 and a separation factor of 1.08.

CONCLUSION

Capillary zone electrophoresis using cyclodextrines as chiral selectors proved to be a suitable method for the enantioseparation of indapamide. Our method is rapid, specific, reliable, and cost-effective and can be proposed for laboratories performing indapamide routine analysis.

Derivatives of diterpen labdane-8α,15-diol as photosynthetic inhibitors in spinach chloroplasts and growth plant inhibitors

In a search of new efficient herbicides of natural origin, four derivatives were prepared from labdane-8α,15-diol (1) and 15-O-acetyl-8α-hydroxy labdane (2) isolated from Croton ciliatoglanduliferus. Their inhibitory activity on photosynthetic electron transport on fresh, broken spinach chloroplasts and on the growth of plants were determined. Derivative 15-O-benzoyl-8α-hydroxy labdane (5) was seven times more active than 2 as reaction Hill inhibitor. Complex of 5 with the adjuvant 2-hydroxypropyl-β-cyclodextrin (5:HPB) (200 μM) was sprayed on Physalys ixocarpa (green tomato) plants; 48 h later the complex inhibited PS II by transforming the active reaction centers to silent reaction centers or "heat sinks". After 72 h this effect disappeared, probably 5:HPB was metabolized by the plant. Chlorophyll a fluorescence of Trifolium alexandrinum (clover) leaves was affected with 5:HPB at the level of PQ pool reduction. 5:HPB decreases the tomato and clover dry-biomass, without affecting Lolium perenne (grass) plants, suggesting that complex 5 acts as selective herbicide for dicotyledonous plants.