Determination of lipophilicity of γ‐butyrolactone derivatives with anticonvulsant and analgesic activity using micellar electrokinetic chromatography

The lipophilicity of a library of 30 derivatives of dihydrofuran‐2(3H)‐one (γ‐butyrolactone) was determined by MEKC. Calibration curve prepared for ten reference drugs enabled to calculate partition coefficient (log P) for novel compounds. The results of MEKC analysis were compared with lipophilicity coefficients determined by RP‐TLC (R_M0) and computational (Mlog P, Clog P) methods. Good correlation was observed between the results obtained by both experimental methods: the MEKC parameters log k and relative lipophilicity R_MO. The relationship between determined log P values and results of the computational prediction was weaker. Analysis of the relationship between lipophilicity and anticonvulsant activity showed statistically significant differences between mean values of log P coefficients for group of active (2.18) and inactive (1.51) compounds in the maximal electroshock test.     

Capillary electrophoresis on unmodified genetically coded amino acids

The separation of mixtures of free genetically coded amino acids by capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography (MEKC) using UV and refractometric detection was studied. Mixtures of 16 and 14 amino acids were separated by CZE and MEKC, respectively.     

Development of a micellar electrokinetic capillary chromatography method for the determination of four naphthalenediols in cosmetics and a comparison with a HPLC method

A micellar electrokinetic capillary chromatography (MEKC) method with ultraviolet visible (UV) detection was used for the determination of 1,7-naphthalenediol, 2,3-naphthalenediol, 1,5-naphthalenediol, and 2,7-naphthalenediol in cosmetics. The current method for their determination in various cosmetics is high-performance liquid chromatography (HPLC). Separation conditions affecting the MEKC method were optimized as 20 mM Na₂B₄O₇–50mM SDS, pH 9.8, with 22 kV applied voltage and UV detection at 230 nm. Under optimal conditions, electrophoretic analysis was completed in less than 6 min, with limit of detection (LOD) of 0.070–0.19 μg/mL and limit of quantitation (LOQ) of 0.23–0.63 μg/mL. A good linear relationship (r² > 0.99) was obtained at the range of 0.75–20 μg/mL. Recoveries for the four naphthalenediols in lotion, loose powder, and sun cream are between 91.2–107.2% with relative standard deviation (RSD) less than 4.04%. The method has been successfully applied to the determination of the four naphthalenediols in different kinds of cosmetics. A comparison with HPLC-UV method was also carried out according to the National Standards of the People's Republic of China. The results obtained by MEKC and HPLC methods are comparable, but the proposed MEKC method can help us obtain a much shorter detection time and low cost.     

Effect of organized media on the chromatographic and electrophoretic determination of pharmaceutical preparations in biological samples

Procedures were developed for the simultaneous determination of endogenous and exogenous steroids in biological fluids by reversed-phase high-performance liquid chromatography (RP HPLC), capillary zone electrophoresis, and micellar electrokinetic chromatography (MEKC) using components of organized media (micelles of sodium dodecyl sulfate, β-cyclodextrin, sulfo-β-cyclodextrin, and carbamide). The detection limits were 50 and 500 ng/mL without preconcentration and 3–5 and 5–10 ng/mL with preconcentration for RP HPLC and MEKC, respectively. The time of separation was 30 and 10 min, and the total time of analysis (including preconcentration and the conditioning of a column or a capillary) was 80 and 90 min for RP HPLC and MEKC, respectively.     

Enantioseparation of esbiothrin by cyclodextrin‐modified microemulsion and micellar electrokinetic chromatography

A comparison between chiral cyclodextrin‐modified microemulsion electrokinetic chromatography (CD‐MEEKC) and cyclodextrin‐modified micellar electrokinetic chromatography (CD‐MEKC) for the enantiomeric separation of esbiothrin was carried out. For both methods, the separation conditions were optimized by varying CD types and concentration, running buffer pH and compositions, organic modifiers, and temperature. The optimal CD‐MEEKC conditions were 0.8% n‐heptane, 2.3% SDS, 6.6% n‐butanol, 90.3% 10 mM sodium tetraborate containing 3% (w/v, the ratio of CD mass to microemulsion volume) methyl‐β‐cyclodextrin, pH 10, 25°C. The optimized CD‐MEKC conditions were 3.3% SDS, 96.7% 10 mM sodium tetraborate containing 5% (w/v) β‐CD, pH 10, 25°C. The difference in physicochemical properties of the buffer and CDs resulted in different optimal CD type. The competitive distribution between the microemulsion (or micelle) and chiral CD contributed to the chiral separation. Both methods provided excellent separation (R_s ～? 3) with similar migration time (ca. 15 min). CD‐MEEKC provided higher separation efficiencies (>300000) than CD‐MEKC (>200000). The LODs for CD‐MEEKC and CD‐MEKC were 4.7 μg/mL and 3.2 μg/mL, respectively. The RSDs of migration time and peak area for CD‐MEEKC were slightly higher than for CD‐MEKC. Both the demonstrated CD‐MEEKC and CD‐MEKC methods provided high efficiencies, low LODs, and reproducible enantioseparations of esbiothrin.     

Determination of ligand efficiency indices in a group of 7H‐purine‐2,6‐dione derivatives with psychotropic activity using micellar electrokinetic chromatography

Discovering hit compounds and optimization processes in medicinal chemistry nowadays could be improved by predictive tools, based on the relationship between structure of molecules and lipophilic properties. Lipophilicity of drug candidate can affect both the pharmacokinetic and pharmacodynamics properties, in particular, the ability of a molecule to cross the cell membrane. Among the new methods for determination of the lipophilicity of compounds, micellar electrokinetic chromatography (MEKC) is considered to be an appropriate one for bioactive molecules, as it closely mimics the physiological conditions. In this paper MEKC was used for the estimation of the lipophilicity of 24 derivatives of 8‐alkoxy‐7H‐purine‐2,6‐dione, designed and synthesized as potential antidepressant/anxiolytic and antipsychotic agents. The results of experimental method were compared with calculated in silico parameters (AlogPs and milogP by Virtual Computational Laboratory website, log P_Pallas by Pallas 3.1, Mlog P by Marvin, log P_ChemS by ChemSketch, log P_ChemDraw by ChemBioUltra) using Principal Component Analysis (PCA) method. Finally, using estimated log P values for selected compounds ligand – lipophilicity efficiency (LLE), per cent efficiency index (PEI), and binding efficiency index (BEI) parameters were calculated. Applied MEKC procedure could be used for selection of potential lead structure in a group of 7H‐purine‐2,6‐dione derivatives.     

Determination of lumiracoxib by a validated stability‐indicating MEKC method and identification of its degradation products by LC‐ESI‐MS studies

A stability‐indicating MEKC method was developed and validated for the analysis of lumiracoxib (LMC) in pharmaceutical formulations using nimesulide as the internal standard (IS). Optimal conditions for the separation of LMC and degradation products were investigated. The method employed 50 mM borate buffer and 50 mM anionic detergent SDS solution at pH 9.0. MEKC method was performed on a fused‐silica capillary (50 μm id; effective length, 40 cm) maintained at 30°C. The applied voltage was 20 kV and photodiode array (PDA) detector was set at 208 nm. The method was validated in accordance with the International Conference on Harmonisation requirements. The stability‐indicating capability of the method was established by enforced degradation studies combined with peak purity assessment using PDA detection. The degradation products formed under stressed conditions were investigated by LC‐ESI‐MS and the two degraded products were identified. MEKC method was linear over the concentration range of 5–150 μg/mL (r²=0.9999) of LMC. The method was precise, accurate, with LOD and LOQ of 1.34 and 4.48 μg/mL, respectively. The robustness was proved by a fractional factorial design evaluation. The proposed MEKC method was successfully applied for the quantitative analysis of LMC in tablets to support the quality control.     

Thermal degradation of phytate produces all four possible inositol pentakisphosphates as determined by ion chromatography and 1H and 31P NMR spectroscopy

Abstract

Decomposition of phytate has recently been shown to occur under mild conditions in the solid state, giving rise to a complex mixture of lower inositol phosphates. In this study, the reaction products of this thermal, abiotic degradation of phytate were separated using ion chromatography and the most highly phosphorylated products subsequently identified using 1D and 2D NMR spectroscopy. Two late eluting fractions were each shown to be a mixture of two specific inositol pentakisphosphate isomers. The peak with shorter retention time contained Ins(1,2,3,4,6)P₅ and DL-Ins(1,2,3,4,5)P₅, while the later eluting fraction contained Ins(1,3,4,5,6)P₅ and DL-Ins(1,2,4,5,6)P₅. The formation of all four possible inositol pentakisphosphate isomers by thermal degradation of phytate contrasts with the selective production of unique inositol pentakisphosphate isomers during enzymatic phytate degradation and therefore suggests a method for differentiating abiotic and biotic processes in environmental samples, including soils and decomposing plant biomass.     

Carbonylation of nitrobenzene in methanol with palladium bidentate phosphane complexes: an unexpectedly complex network of catalytic reactions, centred around a Pd-imido intermediate

The reactivity of palladium complexes of bidentate diaryl phosphane ligands (P₂) was studied in the reaction of nitrobenzene with CO in methanol. Careful analysis of the reaction mixtures revealed that, besides the frequently reported reduction products of nitrobenzene [methyl phenyl carbamate (MPC), N,N′‐diphenylurea (DPU), aniline, azobenzene (Azo) and azoxybenzene (Azoxy)], large quantities of oxidation products of methanol were co‐produced (dimethyl carbonate (DMC), dimethyl oxalate (DMO), methyl formate (MF), H₂O, and CO). From these observations, it is concluded that several catalytic processes operate simultaneously, and are coupled via common catalytic intermediates. Starting from a P₂Pd⁰ compound formed in situ, oxidation to a palladium imido compound P₂Pd^II?NPh, can be achieved by de‐oxygenation of nitrobenzene 1) with two molecules of CO, 2) with two molecules of CO and the acidic protons of two methanol molecules, or 3) with all four hydrogen atoms of one methanol molecule. Reduction of P₂Pd^II?NPh to P₂Pd⁰ makes the overall process catalytic, while at the same time forming Azo(xy), MPC, DPU and aniline. It is proposed that the Pd–imido species is the central key intermediate that can link together all reduction products of nitrobenzene and all oxidation products of methanol in one unified mechanistic scheme. The relative occurrence of the various catalytic processes is shown to be dependent on the characteristics of the catalysts, as imposed by the ligand structure.     

Aggregation of phosphate and 1‐tetradecyl‐3‐methylimidazolium chloride background electrolytes during micellar electrokinetic chromatography

We report the possible aggregation of phosphate and ionic liquid (1‐tetradecyl‐3‐methylimidazolium chloride) based BGEs during MEKC. After a certain transit period, the aggregates appear as a random sequence of spikes on a UV detector signal. Root mean square values of the spikes and aggregation time (T_a) were plotted against BGE concentrations. The observation suggests that MEKC is a simple and easy technique for micelle aggregation studies.     

Application of MEKC and monolithic CEC for the analysis of bioactive naphthoquinones in Eleutherine americana

Two microscale separation techniques for the analysis of bioactive naphthoquinones in Eleutherine americana were developed and validated. By MEKC four compounds (eleuthoside B, isoeleutherin, eleutherol and eleutherinoside A) could be determined in plant extracts using an aqueous electrolyte solution composed of 25 mM sodium tetraborate, 50 mM sodium cholate and 20% THF. CEC on a polymeric methacrylate‐based monolith with strong cationic properties showed promising results, as it additionally enabled the separation of two enantiomers, eleutherin and isoeleutherin. The mobile phase for CEC experiments comprised 3 mM ammonium formate in a mixture of ACN and water. At an applied voltage of ?25 kV, all five markers were baseline separated in less than 12 min. Both methods were successfully validated for linearity (MEKC: R²≥0.999; CEC: R²≥0.997), sensitivity (MEKC: LOD=4–5 μg/mL; CEC: LOD=2–8 μg/mL), accuracy (MEKC: 96.5–102.7% recovery; CEC: 97.1–103.5% recovery) and precision (MEKC: σ_rel≤2.43%; CEC: σ_rel≤2.21%). The quantitative analysis of naphthoquinone derivatives in several E. americana samples showed that both methods are suitable for practical applications, because the results were well comparable to those obtained by established techniques such as HPLC.     

Rapid Estimation of Octanol–Water Partition Coefficient for Triazole Fungicides by MEKC with Sodium Deoxycholate as Surfactant

A rapid estimation of octanol–water partition coefficient (log P _ow) was developed for triazole fungicides by micellar electrokinetic chromatography (MEKC). Five standard compounds with known log P _ow values from 2.9 to 4.3 (cyproconazole, bromuconazole, epoxiconazole, bitertanol and difenoconazole) were used for constructing the calibration curve of the log P _ow against the MEKC retention factor, log k. A linear relationship was achieved between log P _ow and log k, in the MEKC system containing 40 mM sodium deoxycholate (SDC) and 4 mM borate buffer at pH 9.3, with a correlation of determination, r ² = 0.9905. The log P _ow values of four test compounds of triazole fungicides (triadimenol, myclobutanil, propiconazole and penconazole) were calculated based on the log k values measured by MEKC and the slope and intercept of the calibration curve. This MEKC method can give good estimation of the log P _ow of the four test compounds of triazole fungicides with the differences between the literature log P _ow values and estimated log P _ow from the MEKC method were from 0.15 to 0.23 log units.     

Micellar electrokinetic capillary chromatography as an alternative method for determination of hydrocortisone and its most important associated compounds in local pharmaceutical preparations

Summary A new, simple, and accurate micellar electrokinetic chromatographic (MEKC) method is described for quantification of hydrocortisone, hydrocortisone hemisuccinate, hydrocortisone acetate, mystatin, oxytetracycline, Zn-bacitracin, polymyxin B, and lidocaine in ocular and cutaneous pharmaceutical products. The separation was performed at 25°C and 25 kV, with 15mm phosphate +15mm borate buffer, pH 8.2, and 60mm sodium dodecylsulfate (SDS) in 10∶1 (%,v/v) methanol-water as background electrolyte. Under these conditions the analysis time is approximately 23 min. The method has been used for quantification of these compounds in different commercial pharmaceutical products and gave good results when compared with reference spectrophotometric and HPLC methods.     

Comparison of microemulsion electrokinetic chromatography and solvent modified micellar electrokinetic chromatography on rapid separation of heroin, amphetamine and their basic impurities

Microemulsion electrokinetic chromatography (MEEKC) and solvent modified micellar electrokinetic chromatography (MEKC) were investigated with the goal of the rapid separation of complex heroin and amphetamine samples. The rapid simultaneous separation of 17 species of heroin, amphetamine and their basic impurities and adulterants was performed within about 10 min using MEEKC for the first time, whereas solvent modified MEKCs were unable to resolve all the components. The comparisons between MEEKC and solvent modified MEKC proved internal lipophilic organic phase in microemulsions played an important role in improving the separation performance with respect to efficiency. However, the role of internal lipophilic organic phase in MEEKC was disgusted at high concentrations of cosurfactant, and the separations of MEEKC and 1-butanol modified MEKC became similar at high concentrations of 1-butanol. The evaluation of reproducibility, linearity and detection limit of optimized MEEKC method provided good results for all the analytes investigated, thus allowing its application to real controlled drug preparation analysis.     

Allylation Reactions of Aldehydes with Allylboronates in Aqueous Media: Unique Reactivity and Selectivity that are Only Observed in the Presence of Water

Zn(OH)₂‐catalyzed allylation reactions of aldehydes with allylboronates in aqueous media have been developed. In contrast to conventional allylboration reactions of aldehydes in organic solvents, the α‐addition products were obtained exclusively. A catalytic cycle in which the allylzinc species was generated through a B‐to‐Zn exchange process is proposed and kinetic studies were performed. The key intermediate, an allylzinc species, was detected by HRMS (ESI) analysis and by online continuous MS (ESI) analysis. This analysis revealed that, in aqueous media, the allylzinc species competitively reacted with the aldehydes and water. An investigation of the reactivity and selectivity of the allylzinc species by using several typical allylboronates ( 6a , 6b , 6c , 6d ) clarified several important roles of water in this allylation reaction. The allylation reactions of aldehydes with allylboronic acid 2,2‐dimethyl‐1,3‐propanediol esters proceeded smoothly in the presence of catalytic amounts of Zn(OH)₂ and achiral ligand 4d in aqueous media to afford the corresponding syn‐adducts in high yields with high diastereoselectivities. In all cases, the α‐addition products were obtained and a wide substrate scope was tolerated. Furthermore, this reaction was applied to asymmetric catalysis by using chiral ligand 9 . Based on the X‐ray structure of the Zn‐ 9 complex, several nonsymmetrical chiral ligands were also found to be effective. This reaction was further applied to catalytic asymmetric alkylallylation, chloroallylation, and alkoxyallylation processes and the synthetic utility of these reactions has been demonstrated.     

Synthesis and Rearrangement of P‐Nitroxyl‐Substituted PIII and PV Phosphanes: A Combined Experimental and Theoretical Case Study

Low‐temperature generation of P‐nitroxyl phosphane 2 (Ph₂POTEMP), which was obtained by the reaction of Ph₂PH ( 1 ) with two equivalents of TEMPO, is presented. Upon warming, phosphane 2 decomposed to give P‐nitroxyl phosphane P‐oxide 3 (Ph₂P(O)OTEMP) as one of the final products. This facile synthetic protocol also enabled access to P‐sulfide and P‐borane derivatives 7 and 13 , respectively, by using Ph₂P(S)H ( 6 ) or Ph₂P(BH₃)H ( 11 ) and TEMPO. Phosphane sulfide 7 revealed a rearrangement to phosphane oxide 8 (Ph₂P(O)STEMP) in CDCl₃ at ambient temperature, whereas in THF, thermal decomposition of sulfide 7 yielded salt 10 ([TEMP‐H₂][Ph₂P(S)O]). As well as EPR and detailed NMR kinetic studies, indepth theoretical studies provided an insight into the reaction pathways and spin‐density distributions of the reactive intermediates.     

The new way to synthesize ethyl 1-butyryloxy-1-phenylmethane(P-phenyl)phosphinate and whole-cell biocatalysis by Escherichia coli and Pseudomonas fluorescens

Abstract

A new compound, ethyl 1-carboxy-1-hydroxy-1-phenylmethane(P-phenyl)phosphinate, was synthesized and the configuration of its diastereoisomers was described using NMR spectroscopy. Acylation with butyryl chloride gave an unexpected product, ethyl butyryloxy(phenyl)methane(P-phenyl)phosphinate, which was then hydrolyzed using two bacterial species as biocatalysts. Good results were achieved for biocatalytic hydrolysis performed by Escherichia coli cells, giving optically active products with 84% enantiomeric excess, and enantioselectivity of 25.8 for one pair of enantiomers. Better results were obtained when the biocatalytic reaction was carrying out for a longer period and the conversion degree reached 71%, the enantiomeric excess of unreacted substrate was >99% and enantioselectivity increased to 32.1. In all cases, isomers bearing α–carbon atom of S configuration were hydrolyzed preferentially.     

Analysis of estrogens in water by magnetic octadecylsilane particles extraction and sweeping micellar electrokinetic chromatography

A method based on magnetic separation was developed for the extraction of several estrogens (including diethylstilbestrol, estrone and estriol) in water followed by sweeping micellar electrokinetic chromatography (MEKC) analysis with UV detection. Novel magnetic octadecylsilane (ODS) particles were prepared using a silanization method with octadecyl trimethoxysilane as the surface modification reagent of magnetic Fe₃O₄ particles. Octadecyl trimethoxysilane was covalently immobilized on the magnetic iron oxide particles. The particles were used as the sorbents in the magnetic separation for the extraction of trace amounts of estrogens from water. The extraction condition and efficiency of the particles for the estrogens were investigated. Combining the magnetic ODS particles extraction and sweeping MEKC with UV detection, the estrogens at concentrations as low as ng/mL in water can be detected without interference from other substances in the sample matrix.     

Determination of S-adenosylmethionine,S-adenosylhomocysteine,and methylthioadenosine in urine using solvent-modified micellar electrokinetic chromatography

A new approach for direct determination of S-adenosylmethionine (SAM), S-adenosylhomocysteine (SAH), and methylthioadenosine (MTA) in urine was developed based on MEKC by using SDS modified with isobutanol in the presence of PEG-300. Analytes were first extracted with grafted phenylborononic acid. Using a 50 µm internal diameter silica capillary of 32 cm total length filled with 0.05 M SDS, 0.05 M H₃PO₄, 5% (v/v) isobutanol, and 10% (v/v) PEG-300, LOQ of 0.15 µM for SAM and SAH, and 0.2 µM for MTA was reached. Accuracy was 92% for MTA, 109% for SAH, and 105% for SAM, intra- and interday imprecision were <2.5 and ≤3%, respectively. The total time of analysis for one sample was 10 min. Analysis of 30 urine samples from healthy volunteers showed that the median SAM and SAH levels were 12.1 and 0.73 µM, respectively. MTA levels, which were determined in urine for the first time (according to our data), were 0.43 µM, and these values correlated well with the SAM level (r = 0.748, p < 0.01).     

Chromatographic Evaluation of the Lipophilic Properties of Selected Pesticides

Monolinuron, chlortoluron, diuron, isoproturon, linuron, diflubenzuron, dimefuron, teflubenzuron, and lufenuron have been chromatographed on an RP-HPLC column and on RP-HPTLC plates with methanol–water in different volume proportions as mobile phases. The retention values log k, and R_M were extrapolated to zero methanol content. Chromatographic lipophilicities (log k_w, R_Mw, _o(HPLC), and _{o (TLC)}) were compared with measured (log P_exp) partition coefficients and with values (A log Ps, IA log P, C log P, log P_Kowin, and x log P) calculated by use of five different software products. The most significant correlations were found between the chromatographic lipophilicities and C log P values. Satisfactory linear correlation was also obtained between lipophilicity (log k_w, R_Mw) and the valence Gutman index (M).