Direct enantiomeric separation of mianserin and 6-azamianserin derivatives using chiral stationary phases

A New Stability-indicating Chiral RP-HPLC Method for the Determination of Degradation Products in Meclizine Hydrochloride

Background:

An enantiomeric separation of the stability-indicating high-performance liquid chromatographic method was developed and validated for the analysis of Meclizine enantiomers. The degradation behavior of Meclizine Hydrochloride was investigated under different stress conditions recommended by the International Conference on Harmonization (ICH).

Methods:

Enantiomeric resolution of the drug and complete separation from its degradation products were successfully achieved on a Phenomenex® lux cellulose 1 C18 (250 mm × 4.6 mm i.d, 5 μm particle size) column, using UV detector at a wavelength of 230 nm, with a mobile phase consisting of acetonitrile, 20mM ammonium bicarbonate at the ratio of 75:25 (v/v), and a flow rate of 1 mL/min. The drug was subjected to alkaline, acidic, neutral, oxidative and photolytic conditions in order to mimic stress conditions.

Result:

The degradation products were well resolved from main peak and proving the stability-indicating power of the method. The developed method provided linear responses within the concentration range 1-5 µg/mL, and regression analysis showed a correlation coefficient value (r2) of 0.999. The HPLC method was validated as per ICH guidelines with respect to specificity, precision, linearity and robustness. Limit of detection (LOD) and limit of quantification (LOQ) were found to be 0.25 µg/mL and 1.00 µg/mL respectively.

Conclusion:

The method provides good sensitivity and excellent precision and reproducibility. The method was highly selective, where degradation products and co formulated compounds did not interfere. The proposed method was successfully applied in pharmaceutical preparations.

Pharmacokinetics of mirtazapine: enantioselective effects of the CYP2D6 ultra rapid metabolizer genotype and correlation with adverse effects

Enantiomerically pure drugs and genotyping are promising approaches to achieve optimization in antidepressant therapy. Mirtazapine is a mixed noradrenergic serotoninergic antidepressant used as a racemate. We analyzed pharmacokinetics of its enantiomers in relation to CYP2D6 genotype and in relation to its adverse effects. Mirtazapine was enantioselectively absorbed from the gut with a rate constant of 0.2 min-1 for S+, but 0.08 min-1 for R- mirtazapine. Kinetics of R- mirtazapine was only marginally dependent on CYP2D6 genotype, but total clearance of the S+ enantiomer were 1.3, 2.3, and 3.4 L min-1 in poor, extensive, and ultrarapid metabolizers of CYP2D6 substrates with apparent substantial first-pass metabolism in rapid and ultrarapid metabolizers. Mirtazapine effects on heart rate and blood pressure correlated much more strongly with R- then with S+ concentrations, whereas sedation correlated similarly with both enantiomers. At least concerning some adverse effects, it might be worthwhile to study further mirtazapine enantiospecifically.

Direct HPLC enantioseparation of chiral aptazepine derivatives on coated and immobilized polysaccharide-based chiral stationary phases

The direct HPLC enantioseparation of Mianserin and a series of aptazepine derivatives is accomplished on polysaccharide-based chiral stationary phases (CSPs). The resolutions are performed on the coated-type Chiralcel OD and Chiralpak AD CSPs and on the first commercially available immobilized-type Chiralpak IA CSP, in normal-phase and polar-organic modes. The complete separation of enantiomers of all racemates investigated was successfully achieved under at least one of CSP/eluent combinations employed. Pure alcohols such ethanol or 2-propanol, with a fixed percentage of DEA added, serve as valuable alternatives to the more common n-hexane-based normal-phase eluents in resolution of Mianserin on the AD CSP. In order to study the chiroptical properties of aptazepine derivatives, chromatographic resolutions are carried out at semipreparative scale using Chiralpak AD and Chiralpak IA as CSPs. Nonconventional dichloromethane-based eluents have permitted to expand the chiral resolving ability of the immobilized Chiralpak IA CSP and to perform mg-scale enantioseparations with an analytical-size column. Assignment of the absolute configuration of the separated enantiomers is empirically established by comparing their chiroptical data with those of structurally related Mianserin.

Determination of the enantiomeric purity of nucleoside analogs related to d4T and acyclovir, new potential antiviral agents, using liquid chromatography on cellulose chiral stationary phases

We reported a method of determination of enantiomeric purity of the new potential antiviral agents by direct analytical HPLC. Those agents are nucleoside analogs, having one chiral center. They are synthesized as a single enantiomer (R or S) by an asymmetric pathway. The chiral stationary phases chosen are silica-based cellulose tris-3,5-dimethylphenylcarbamate (Chiralcel OD-H), or tris-methylbenzoate (Chiralcel OJ). Resolution was achieved using normal-phase chromatography with a mobile phase consisting of n-hexane-alcohol (ethanol or 2-propanol) in various percentages. Furthermore the effects of structural features on retention, selectivity and resolution, as well as on the elution order were thoroughly studied. Differences in the lipophilicity of the compounds were also examined.

Synthesis and pharmacological testing of 1,2,3,4,10,14b-hexahydro-6-methoxy-2-methyldibenzo[c,f]pyrazino[1,2-a]azepin and its enantiomers in comparison with the two antidepressants mianserin and mirtazapine

The synthesis and resolution of 1,2,3,4,10,14b-hexahydro-6-methoxy-2-methyldibenzo[c,f]pyrazino[1,2-a]azepin (6-methoxymianserin, 6) are described. Furthermore, the in vitro and in vivo effects of 6 and its enantiomers are presented. 6 displayed high affinity for the 5-HT2A/2C receptors, only moderate affinity for the adrenoceptors, and no affinity for the NA reuptake site. Surprisingly, 6 also showed moderate to high affinity for the dopamine D2 receptor, an effect that resides in the (R)-(-)-enantiomer.

Determination of mirtazapine in tablets by UV spectrophotometric and derivative spectrophotometric methods

Mirtazapine, 1, 2, 3, 4, 10, 14b-hexahydro-2-methyl-pyrazino [2, 1-a] pyrido [2, 3-c] [G.L. Stimmel, J.A. Dopheide and S.M. Stahl, Pharmacotheraphy 17(1) (1997) 10] benzazepine, is a new and well tolerated antidepressant. It blocks pre-synaptic alpha2-adrenergic receptors and postsynaptic serotonin type 2 and type 3 receptors. The drug is rapid and completely absorbed after oral administration. Mirtazapine was analyzed by HPLC and gas chromatography with nitrogen-sensitive detection. In this study, mirtazapine was analyzed by using UV spectrophotometry, first and second order derivative spectrophotometry. The type of solvent, the degree of derivation, range of wavelength and n value were chosen in order to optimize the conditions. The concentration of mirtazapine in its methanolic solutions were determined between the wavelength range of 225-360 nm in the linearity range of 1-100, 2-100 and 1-120 microg ml(-1) by using the values obtained from UV. first-order derivative (n = 5, delta lambda = 17.5 nm) and second-order derivative (n = 9, delta lambda = 31.5 nm) spectrum of the substance, respectively. The developed UV Spectrophotometric, first-order and second-order derivative spectrophotometric methods were applied to a pharmaceutical preparation as tablet form. Developed UV and derivative UV spectrophotometric method in this study are accurate, sensitive, precise, reproducible and can be directly and easily applied to the pharmaceutical preparations.