Stereoselective determination and pharmacokinetics of dihydropyridines: an updated review

Enhanced Chiral Recognition Abilities of Cyclodextrin Covalent Organic Frameworks via Chiral/Achiral Functional Modification

β-Cyclodextrin covalent organic frameworks (β-CD COFs) show great potential in enantioseparation due to their uniformly distributed chiral recognition sites and good chemical stability. The hydroxyl and amino groups of β-CD COFs enable facile post-modification to introduce the desired functionality into the frameworks. In this study, we perform post-modification of β-CD COF_BPDA with 1,4-butane sultone and [(3R,4R)-4-acetyloxy-2,5-dioxooxolan-3-yl] acetate to construct two kinds of novel functional β-CD COFs. The capillary columns prepared with these two functional β-CD COFs separated chiral dihydropyridines and fluoroquinolones with excellent selectivity and repeatability in capillary electrochromatography, while β-CD COF_BPDA-modified capillary columns did not present the chiral recognition ability for these drugs. The mechanism of chiral recognition and the enhanced enantioselectivity of functional β-CD COFs were further demonstrated by molecular docking simulation. The divergent chiral separation performances of β-CD COFs suggest that the introduction of functional groups enables the modification of β-CD COF properties and tuning of its chiral recognition abilities for the diversity of enantioseparation.

Electrochemical determination of calcium channel blocker drugs using multiwall carbon nanotube-modified glassy carbon electrode

Background

Calcium channel blockers belonging to the dihydropyridine family have been used as a potent arterial vasodilator in the management of angina and cardiovascular diseases. In the design of glassy carbon electrode coatings for the study of the same, multiwall carbon nanotubes (MWCNT) are favored. They are known for the reduction and oxidation of electroactive species towards cathodic and anodic direction with the simultaneous enhancement of the peak current.

Results

The MWCNT-modified glassy carbon electrode exhibited a sharp anodic peak potential at around at 0.5 V for amlodipine (AMLD) andnimodipine (NIMD), and 0.4 V for felodipine (FELD) in the cyclic voltammograms. The antihypertensive drugs were determined using a simple two-step procedure developed which comprised a preconcentration step followed by the differential pulse stripping voltammetric quantification. Concentration calibrations were linear within the range from 0.01 to 0.3 μg/mL for AMLD and FELD, and 0.025 to 0.3 μg/mL for NIMD.

Conclusion

The lower limit detection (LOD) was found to be very low on modified electrode. The LOD is 0.005 μg/mL for AMLD and FELD, and 0.01 μg/mL for NIMD. The prepared electrode showed an excellent electrocatalytic activity towards the oxidation of antihypertensive drugs leading to a remarked improvement in sensitivity. An electrochemical sensor featuring the MWCNT-modified electrode was applied successfully as the result for the calcium channel blocker determination in pharmaceutical samples.

Enantiomeric recognition of racemic 4-aryl-1,4-dihydropyridine derivatives via chiralpak AD-H stationary phases

The chromatographic chiral resolution of two new series of racemic 4-substituted-1,4-dihydropyridine derivatives was studied on a commercial Chiralpak AD-H column. Analytes without 5,5-dimethyl substituents (1-15) are more efficiently resolved than analytes with 5,5-dimethyl groups (16-30). The AD-H column discriminated between enantiomers through both hydrogen bonding attractions and π-π interactions. This interpretation is in accord with plots of the logarithm of separation factors, log(α), versus σ (Hammett-Swain substituent parameter) and σ(+) (Brown substituent constant) plots. By elucidating the effects of the remote substituents on these chiral separations, it was shown that the influence of π-π interaction forces increase when steric bulk effects act to decrease the hydrogen bonding attractive forces on the AD-H column.

Pharmacologically active compounds in the environment and their chirality

Pharmacologically active compounds including both legally used pharmaceuticals and illicit drugs are potent environmental contaminants. Extensive research has been undertaken over the recent years to understand their environmental fate and toxicity. The one very important phenomenon that has been overlooked by environmental researchers studying the fate of pharmacologically active compounds in the environment is their chirality. Chiral drugs can exist in the form of enantiomers, which have similar physicochemical properties but differ in their biological properties such as distribution, metabolism and excretion, as these processes (due to stereospecific interactions of enantiomers with biological systems) usually favour one enantiomer over the other. Additionally, due to different pharmacological activity, enantiomers of chiral drugs can differ in toxicity. Furthermore, degradation of chiral drugs during wastewater treatment and in the environment can be stereoselective and can lead to chiral products of varied toxicity. The distribution of different enantiomers of the same chiral drug in the aquatic environment and biota can also be stereoselective. Biological processes can lead to stereoselective enrichment or depletion of the enantiomeric composition of chiral drugs. As a result the very same drug might reveal different activity and toxicity and this will depend on its origin and exposure to several factors governing its fate in the environment. In this critical review a discussion of the importance of chirality of pharmacologically active compounds in the environmental context is undertaken and suggestions for directions in further research are made. Several groups of chiral drugs of major environmental relevance are discussed and their pharmacological action and disposition in the body is also outlined as it is a key factor in developing a full understanding of their environmental occurrence, fate and toxicity. This review will be of interest to environmental scientists, especially those interested in issues associated with environmental contamination with pharmacologically active compounds and chiral pollutants. As the review will outline current state of knowledge on chiral drugs, it will be of value to anyone interested in the phenomenon of chirality, chiral drugs, their stereoselective disposition in the body and environmental fate (212 references).

Capillary electrophoretic enantioseparation of m-nisoldipine using two different beta-cyclodextrins

The methods for the enantioseparation of m-nisoldipine, a new 1,4-dihydropyridine calcium ion antagonist, were developed. The elaborated methods of m-nisoldipine enantiomers separation were successfully performed using an anionic CD-sulfobutyl ether-beta-CD (SBE-beta-CD) or carboxymethyl-beta-CD as chiral selector. However, the results indicated that SBE-beta-CD was a better chiral selector for enantioseparation of the neutral m-nisoldipine. Furthermore, comparing the two SBE-beta-CDs, the derivative with a higher degree of substitution (DS) of 7.0 induced better enantioresolution than the one with low DS (4.0). In addition, possible chiral recognition mechanisms of dihydropyridines were discussed.

Characterization of benidipine and its enantiomers' metabolism by human liver cytochrome P450 enzymes

Benidipine is a dihydropyridine calcium antagonist that has been used clinically as an antihypertensive and antianginal agent. It is used clinically as a racemate, containing the (-)-alpha and (+)-alpha isomers of benidipine. This study was performed to elucidate the metabolism of benidipine and its enantiomers in human liver microsomes (HLMs) and to characterize the cytochrome P450 (P450) enzymes that are involved in the metabolism of benidipine. Human liver microsomal incubation of benidipine in the presence of NADPH resulted in the formation of two metabolites, N-desbenzylbenidipine and dehydrobenidipine. The intrinsic clearance (CL(int)) of the formation of N-desbenzylbenidipine and dehydrobenidipine metabolites from (-)-alpha isomer was similar to those from the (+)-alpha isomer (1.9 +/- 0.1 versus 2.3 +/- 2.3 microl/min/pmol P450 and 0.5 +/- 0.2 versus 0.6 +/- 0.6 microl/min/pmol P450, respectively). Correlation analysis between the known P450 enzyme activities and the rate of the formation of benidipine metabolites in the 15 HLMs showed that benidipine metabolism is correlated with CYP3A activity. The P450 isoform-selective inhibition study in liver microsomes and the incubation study of cDNA-expressed enzymes also showed that theN-debenzylation and dehydrogenation of benidipine are mainly mediated by CYP3A4 and CYP3A5. The total CL(int) values of CYP3A4-mediated metabolite formation from (-)-alpha isomer were similar to those from (+)-alpha isomer (17.7 versus 14.4 microl/min/pmol P450, respectively). The total CL(int) values of CYP3A5-mediated metabolite formation from (-)-alpha isomer were also similar to those from (+)-alpha isomer (8.3 versus 11.0 microl/min/pmol P450, respectively). These findings suggest that CYP3A4 and CYP3A5 isoforms are major enzymes contributing to the disposition of benidipine, but stereoselective disposition of benidipine in vivo may be influenced not by stereoselective metabolism but by other factors.

Pathophysiological Significance of T-type Ca2+ Channels: T-type Ca2+ Channels and Drug Development

T-type Ca(2+) channels are present in cardiovascular, neuronal, and endocrine systems; and they are now receiving attention as novel therapeutic targets. Many drugs and compounds non-specificaly block T-type Ca(2+) channels. Certain dihydropyridine compounds, such as efonidipine, have blocking activity on both L-type and T-type Ca(2+) channels which possibly underlies their excellent clinical profiles such as minimum reflex tachycardia and renal protection. Selective inhibitors of T-type Ca(2+) channels, such as non-hydrolyzable mibefradil and R(-)-efonidipine, are powerful pharmacological tools for further studies and may lead to the development of novel therapeutic strategies.

Separation of neutral dihydropyridines and their enantiomers using electrokinetic chromatography

The separation and simultaneous enantiomeric separation of three neutral 1,4-dihydropyridine (DHP) derivatives (nimodipine, nisoldipine and nitrendipine) was studied using electrokinetic chromatography. Bile salts allowed the non-chiral separation of these DHP derivatives. With the taurine-conjugated bile salts a beginning of enantiomeric separation was observed for nimodipine and nisoldipine. Achiral micelles of sodium dodecyl sulphate mixed with neutral cyclodextrins did not allow enantioseparation. Baseline chiral separation of nisoldipine and nimodipine was obtained with carboxymethyl-beta-cyclodextrin at pH 5.0. The buffer type affected the chiral separation, especially in the case of nisoldipine. The addition of organic solvent decreased the enantioresolution of nimodipine. However, the resolution between the nisoldipine enantiomers was increased when methanol or ethanol were added to the background electrolyte. Varying the temperature had almost no effect on the enantioresolution of nisoldipine, whereas with nimodipine a clear improvement at lower temperatures was observed. Using the optimised method, the selectivity of this method was investigated for three possible impurities of nisoldipine.

Enantioselective determination of lercanidipine in human plasma for pharmacokinetic studies by normal-phase liquid chromatography–tandem mass spectrometry

We describe here the first method for the enantioselective analysis of the calcium antagonist lercanidipine in human plasma by high performance liquid chromatography (HPLC) employing tandem mass spectrometric (MS) detection. Routine determination of lercanidipine enantiomers in human plasma in the working range of 0.025-50.0 ng ml(-1) plasma for each enantiomer with an accuracy and precision less than 15% was possible. Application of the method to a stereospecific study of the pharmacokinetics showed that plasma levels after an oral dose of rac-lercanidipine administered to a healthy volunteer were found to be higher for the (S)-enantiomer.