Chiral recognition of dapoxetine enantiomers with methylated-gamma-cyclodextrin: a validated capillary electrophoresis method

Chiral Materials: Progress, Applications, and Prospects

Chirality is a universal phenomenon in molecular and biological systems, denoting an asymmetric configurational property where an object cannot be superimposed onto its mirror image by any kind of translation or rotation, which is ubiquitous on the scale from neutrinos to spiral galaxies. Chirality plays a very important role in the life system. Many biological molecules in the life body show chirality, such as the "codebook" of the earth's biological diversity-DNA, nucleic acid, etc. Intriguingly, living organisms hierarchically consist of homochiral building blocks, for example, l-amino acids and d-sugars with unknown reason. When molecules with chirality interact with these chiral factors, only one conformation favors the positive development of life, that is, the chiral host environment can only selectively interact with chiral molecules of one of the conformations. The differences in chiral interactions are often manifested by chiral recognition, mutual matching, and interactions with chiral molecules, which means that the stereoselectivity of chiral molecules can produce changes in pharmacodynamics and pathology. Here, the latest investigations are summarized including the construction and applications of chiral materials based on natural small molecules as chiral source, natural biomacromolecules as chiral sources, and the material synthesized by design as a chiral source.

Application of Experimental Design Methodologies in the Enantioseparation of Pharmaceuticals by Capillary Electrophoresis: A Review

Chirality is one of the major issues in pharmaceutical research and industry. Capillary electrophoresis (CE) is an interesting alternative to the more frequently used chromatographic techniques in the enantioseparation of pharmaceuticals, and is used for the determination of enantiomeric ratio, enantiomeric purity, and in pharmacokinetic studies. Traditionally, optimization of CE methods is performed using a univariate one factor at a time (OFAT) approach; however, this strategy does not allow for the evaluation of interactions between experimental factors, which may result in ineffective method development and optimization. In the last two decades, Design of Experiments (DoE) has been frequently employed to better understand the multidimensional effects and interactions of the input factors on the output responses of analytical CE methods. DoE can be divided into two types: screening and optimization designs. Furthermore, using Quality by Design (QbD) methodology to develop CE-based enantioselective techniques is becoming increasingly popular. The review presents the current use of DoE methodologies in CE-based enantioresolution method development and provides an overview of DoE applications in the optimization and validation of CE enantioselective procedures in the last 25 years. Moreover, a critical perspective on how different DoE strategies can aid in the optimization of enantioseparation procedures is presented.

Native and synchronous fluorescence spectroscopy for determination of avanafil in presence of its co-formulated drug (dapoxetine hydrochloride): Application to pharmaceutical product, biological fluid and content uniformity

The native and synchronous fluorescence spectroscopy procedures have been established and validated for the simultaneous determination of a binary mixture of dapoxetine hydrochloride (DAP) and avanafil (AVA). The first procedure is based on measurement of native fluorescence intensity of both drugs at λ_Em 337 nm and 370 nm using λ_Ex 290 nm and 314 nm for DAP and AVA in methanol respectively. The second procedure describes a measurement of synchronous fluorescence intensity of these drugs at 232 nm for DAP, and 267 nm for AVA, using Δλ of 90nm. In the first procedure the fluorescence concentration were 0.1-4.0 μg/mL for DAP and 0.5-16 μg/mL for AVA. For the second procedure fluorescence concentrations were 0.025-1.0 μg/mL and 0.5-16 μg/mL for DAP and AVA respectively, with lower detection limit and quantification limits. The processes were successfully used for the limitation of DAP and AVA in their drug product without pre-separation. Then, the techniques were utilized for the determination of DAP and AVA in biological fluids. There is a good agreement between these results and the results obtained using a reference method.

Capillary electrophoresis method for the determination of (R)-dapoxetine, (3S)-3-(dimethylamino)-3-phenyl-1-propanol, (S)-3-amino-3-phenyl-1-propanol and 1-naphthol as impurities of dapoxetine hydrochloride

A capillary electrophoresis method was developed and validated for the determination of the purity of dapoxetine with regard to the related substances (3S)-3-amino-3-phenylpropan-1-ol, (3S)-3-(dimethylamino)-3-phenylpropan-1-ol, 1-naphthol and the enantiomer (R)-dapoxetine. The separation was based on a dual selector system, which was optimized by a fractional factorial resolution V + design followed by a central composite face centered design with star distance 1 and Monte Carlo simulations for defining the design space. The optimized background electrolyte consisted of a 50 mM sodium phosphate buffer, pH 6.3, containing 45 mg/mL sulfated γ-cyclodextrin and 40.2 mg/mL 2,6-dimethyl-β-cyclodextrin. Separations were carried out in a 23.5/32 cm, 50 μm fused-silica capillary employing a separation voltage of 9 kV at 15 °C. Following robustness testing using a Plackett-Burman design the method was validated according to the International Council on Harmonization guideline Q2(R1) in the range of 0.05-1.0% relative to the dapoxetine concentration. The method was applied to the analysis of drug substance and a commercial tablet. Data regarding the enantiomeric purity of dapoxetine obtained by the capillary electrophoresis assay were comparable to the data obtained by an enantioselective HPLC method.

Electrochemical Determination of the Serotonin Reuptake Inhibitor, Dapoxetine, Using Cesium-Gold Nanoparticles

Cesium-gold (Cs-Au) nanoparticles are shown to be analytically advantageous for the electroanalytical sensing of dapoxetine (DPX), a serotonin reuptake inhibitor used for the treatment of premature ejaculation. The Cs-Au nanoparticles are electrically wired and supported upon mass producible, economical screen-printed electrochemical sensing platforms and are characterized electrochemically (cyclic voltammetry and electrochemical impedance spectroscopy) and physiochemically (field emission scanning electron microscopy and energy dispersive X-ray analysis). The face-centered design was applied to optimize the significant experimental factors by using square wave voltammetry. The Cs-Au-based sensor is found to exhibit a large linear range (10-7 to 10-4 M) with a good analytical linearity with the limits of detection and quantification corresponding to 2.50 × 10-10 and 8.33 × 10-8 M, respectively. The developed sensor was successfully applied in the quantification of DPX in the presence of sildenafil, both of which are commonly found within combined dose tablet pharmaceutical formulations. The proposed DPX electrochemical Cs-Au-based sensor has the advantages of being single-shot and disposable and is shown to be successful in determining DPX in pharmaceutical formulations, human urine, and serum samples with acceptable recoveries.

Development and validation of a cyclodextrin-modified capillary electrophoresis method for the enantiomeric separation of vildagliptin enantiomers

The enantiomers of vildagliptin, an orally available and selective dipeptidyl-peptidase-4 inhibitor used for the treatment of type II diabetes, have been separated by CD-modified CZE, using uncoated fused-silica capillary. After screening 13 negatively charged CD derivatives as potential chiral selectors, sulfobutyl-ether-α-CD (SBE-α-CD) was selected for the enantioseparation. For the optimization, a factorial analysis study was performed by orthogonal experimental design. Six experimental factors were chosen as variable parameters: temperature, applied voltage, chiral selector and BGE concentrations, pH, and the parameters of the hydrodynamic injection. The optimized system still was not considered final as the second peak (S-enantiomer) migrated too close to the EOF, resulting in a potential inaccuracy during the determination of the chiral impurity. To fine-tune the method "one factor at a time" variation approach was applied. The final method (applying 15°C capillary temperature, 40 mbar × 4 s hydrodynamic injection, 25 kV voltage in 75 mM acetate-Tris buffer [pH 4.75] containing 20 mM SBE-α-CD as chiral selector) was validated according to the ICH guideline. RSD percentage of the resolution value, migration times, and corrected peak areas were below 5% during testing repeatability and intermediate precision. LOD and LOQ values were found to be 2.5 and 7.5 μg/mL, respectively. The method is considered linear in the 7.5-180 μg/mL range for the R-enantiomer. The robustness of the method was justified using Plackett-Burmann statistical experimental design.

NMR, CD and UV spectroscopic studies reveal uncommon binding modes of dapoxetine to native cyclodextrins

Complex formation between the selective serotonin reuptake inhibitor drug (S)-dapoxetine (Dpx) and β-, γ-, and methylated γ-cyclodextrins (CyDs) was studied by complementary experimental techniques.

Chiral separation of asenapine enantiomers by capillary electrophoresis and characterization of cyclodextrin complexes by NMR spectroscopy, mass spectrometry and molecular modeling

The enantiomers of asenapine maleate (ASN), a novel antipsychotic against schizophrenia and mania with bipolar I disorder have been separated by cyclodextrin (CD) modified capillary zone electrophoresis for the first time. 15 different CDs were screened as complexing agents and chiral selectors, investigating the stability of the inclusion complexes and their enantiodiscriminating capacities. Although initially, none of the applied chiral selectors gave baseline separation, β-CD proved to be the most effective chiral selector. In order to improve resolution, an orthogonal experimental design was employed, altering the concentration of background electrolyte, organic modifier, pH, capillary temperature and applied voltage in a multivariate manner. The developed method (160 mM TRIS-acetate buffer pH 3.5, 7 mM β-CD, at 20 °C, applying 15 kV) was successful for baseline separation of ASN enantiomers (R(s)=2.40±0.04). Our method was validated according to ICH guidelines and proved to be sensitive, linear, accurate and precise for the chiral separation of ASN. Properties of the inclusion complexes, such as stoichiometry, atomic level intermolecular host-guest connections are proposed on the basis of ROESY NMR measurement, ESI-MS spectrometry and molecular modeling studies. It was found that the ASN-β-CD complex is of 1:1 composition, and either of the aromatic rings can be accommodated in the β-CD cavity.

Structure elucidation of a process-related impurity of dapoxetine

Unknown by-product associated with the synthesis of dapoxetine was isolated. The structure elucidation of this new compound using accurate mass data and NMR spectroscopy is presented herein. The unambiguous resonance assignment concluded to the formation of a tricyclic compound 4-phenyl-2H,3H,4H-naphtho[1,2-b]pyran, a new impurity of dapoxetine which has never been reported previously. A proposed mechanism for the formation of the new carbon-carbon bond is discussed. For the separation of dapoxetine and the process-related impurities, a gradient HPLC method was developed.

Tapentadol enantiomers: Synthesis, physico-chemical characterization and cyclodextrin interactions

The complete physico-chemical characterization of the single enantiomer analgesic drug R,R-tapentadol was quantitated in terms of protonation macro- and microconstants and octanol-water partition coefficient using pH-potentiometry, UV-pH and (1)H NMR-pH titrations. The protonation macroconstants were found to be logK1=10.59±0.01 and logK2=9.44±0.01, while the individual basicity of each protonation site was found to be logk(O)=9.94 and logk(N)=10.48 for the phenolate and tertiary amine functions, respectively. As a consequence, the zwitterionic form of tapentadol predominates in aqueous solutions. The potential optical impurity (S,S-tapentadol) was synthesized for the first time in a seven-step chiral synthetic procedure. The enantiomers of tapentadol were separated by cyclodextrin modified capillary zone electrophoresis. Over 15 cyclodextrins were investigated in terms of apparent complex stability and screened as chiral selectors, and the sulfated alpha-cyclodextrin was found to resolve the enantiomers with excellent resolution (Rs=16.2 and 9.1) at pH 4.75 and pH 9.0, respectively. The system containing 12mM selector in a 50mM TRIS-acetate buffer was amenable to detect S,S-tapentadol potential optical impurity at 0.1% concentration level.

Multivariate optimization of capillary electrophoresis methods: a critical review

In this article a review on the recent applications of multivariate techniques for optimization of electromigration methods, is presented. Papers published in the period from August 2007 to February 2013, have been taken into consideration. Upon a brief description of each of the involved CE operative modes, the characteristics of the chemometric strategies (type of design, factors and responses) applied to face a number of analytical challenges, are presented. Finally, a critical discussion, giving some practical advices and pointing out the most common issues involved in multivariate set-up of CE methods, is provided.