Enantioseparation and Determination of Mephedrone and Its Metabolites by Capillary Electrophoresis Using Cyclodextrins As Chiral Selectors
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molecules Article Enantioseparation and Determination of Mephedrone and Its Metabolites by Capillary Electrophoresis Using Cyclodextrins as Chiral Selectors Pavel Rezankaˇ 1,* , Denisa Macková 1, Radek Jurok 2,3, Michal Himl 3 and Martin Kuchaˇr 2 1 Department of Analytical Chemistry, Faculty of Chemical Engineering, University of Chemistry and Technology, Prague, Technická 5, 166 28 Prague 6, Czech Republic; [email protected] 2 Department of Chemistry of Natural Compounds, Forensic Laboratory of Biologically Active Substances, Faculty of Food and Biochemical Technology, University of Chemistry and Technology, Prague, Technická 5, 166 28 Prague 6, Czech Republic; [email protected] (R.J.); [email protected] (M.K.) 3 Department of Organic Chemistry, Faculty of Chemical Technology, University of Chemistry and Technology, Prague, Technická 5, 166 28 Prague 6, Czech Republic; [email protected] * Correspondence: [email protected] Academic Editor: Estrella Núñez Delicado Received: 25 May 2020; Accepted: 19 June 2020; Published: 23 June 2020 Abstract: Mephedrone, a psychoactive compound derived from cathinone, is widely used as a designer drug. The determination of mephedrone and its metabolites is important for understanding its possible use in medicine. In this work, a method of capillary electrophoresis for the chiral separation of mephedrone and its metabolites was developed. Carboxymethylated β-cyclodextrin was selected as the most effective chiral selector from seven tested cyclodextrin derivates. Based on the simplex method, the optimal composition of the background electrolyte was determined: at pH 2.75 and 7.5 mmol L 1 carboxymethylated β-cyclodextrin the highest total resolution of a mixture of analytes · − was achieved. For mephedrone and its metabolites, calibration curves were constructed in a calibration range from 0.2 to 5 mmol L 1; limits of detection, limits of quantification, precision, and repeatability · − were calculated, and according to Mandel’s fitting test, the linear calibration ranges were determined. Keywords: capillary electrophoresis; chiral separation; cyclodextrin; mephedrone; metabolites 1. Introduction Mephedrone, a psychostimulant drug first synthesized in the 1920s, is classified as a synthetic cathinone [1]. According to the European Monitoring Centre for Drugs and Drug Addiction [2], synthetic cathinones, together with synthetic cannabinoids, are the most abundant substances in the group of so-called new psychoactive substances. In most cases, these drugs have stimulant entactogenic effects; however, the biological activity of such substances is difficult to predict and some of these artificially prepared substances have been shown to have potential therapeutic uses [3], for example, bupropion is used to treat depression and smoking cessation [4] and diethylpropion is prescribed as an anti-obesity drug [5]. On the other hand, pyrovalerone has been prescribed for the treatment of chronic obesity and lethargy but has been withdrawn for its abuse by patients [4,6]. These new psychoactive substances can also mimic prescription therapeutic psychoactive drugs; for example, phenmetrazine, modafinil, and methylphenidate, and hence are more available even for healthy people because they are available on the Internet [7]. So, an intensive study of these compounds is needed. The most commonly used techniques for isolating new psychoactive substances from biological samples are liquid-to-liquid extraction (LLE) and solid-phase extraction (SPE) [8]. LLE is a simple method, but its problems are easy contamination and matrix influence. On the contrary, the SPE is very selective but time-consuming [9]. A popular method is the QuEChERS method (quick, easy, cheap, Molecules 2020, 25, 2879; doi:10.3390/molecules25122879 www.mdpi.com/journal/molecules Molecules 2020, 25, x FOR PEER REVIEW 2 of 12 healthy people because they are available on the Internet [7]. So, an intensive study of these compounds is needed. The most commonly used techniques for isolating new psychoactive substances from biological samples are liquid-to-liquid extraction (LLE) and solid-phase extraction (SPE) [8]. LLE is a simple Molecules 2020, 25, 2879 2 of 12 method, but its problems are easy contamination and matrix influence. On the contrary, the SPE is very selective but time-consuming [9]. A popular method is the QuEChERS method (quick, easy, echeap,ffective, effective, rugged, rugged, and safe) and modified safe) modified in 2012 in for 2012 the for extraction the extraction of psychoactive of psychoactive substances substances from biologicalfrom biological samples samples [10]. [10]. Simple colorimetric colorimetric tests tests are used are for used rapid for orientation rapid orientationdetection of detectiondrugs. However, of drugs. the However,identification the identificationis very indicative,is very detecting indicative, only detecting the presence only theof presencecertain structural of certain motifs structural [11]. motifsHowever, [11 ].immunologicalHowever, immunological methods that methods are commethat arercially commercially available are available more arecommonly more commonly used for usedrapidfor drug rapid detection. drug detection. However, However, there is no there sufficiently is no suffi effectiveciently e ffimmunoassayective immunoassay on the market on the marketfor the fordetection the detection of cathinones of cathinones that does that not does show not cross-reactivity show cross-reactivity between between analogs analogs [9,12,13]. [9, 12,13]. Of the advanced chromatographic techniques, gas and liquid chromatography with a mass spectrometer (GC-MS (GC-MS and and LC-MS) LC-MS) ar aree the the most most suitable suitable for for the the analysis analysis of ofsynthetic synthetic cathinones. cathinones. In Ingeneral, general the, the GC-MS GC-MS technique technique is used is used more more for drug for drug analysis, analysis, mainly mainly due to due shorter to shorter elution elution times times[14–19]. [14 Chiral–19]. Chiral separation separation is mo isst most often often performed performed in inan anachiral achiral environment environment after after the the previous conversion of enantiomers to diastereoisomers [20], [20], which, however, brings complications for the quantificationquantification itself [[21].21]. It should be also notednoted thatthat cathinonescathinones areare thermodegradablethermodegradable substancessubstances and due due to to the the thermal thermal conditions conditions necessary necessary for sepa for separationration by GC, by their GC, partial their partial decomposition decomposition occurs occurs[5]. Therefore, [5]. Therefore, LC-MS LC-MS[22–24] [and22– 24LC-UV] and LC-UV[25,26] usin [25,26g a] usingchiral astationary chiral stationary or mobile or phase mobile is phaseoften isused. often Rapid used. separation Rapid separation of cathinones of cathinones is also poss is alsoible possible by supercritical by supercritical fluid chromatography fluid chromatography (SFC) (SFC)[27,28]. [ 27Carnes,28]. etCarnes al. compared et al. compared the separation the separation of cathinones of cathinones by ultrahigh by efficiency ultrahigh SFC effi ciency(UHPSFC), SFC (UHPSFC),ultrahigh efficiencyultrahigh LC effi (UHPLC)ciency LC with (UHPLC) a non-pola withr acolumn, non-polar UHPLC column, with UHPLC a hydrophilic with a column, hydrophilic and column,GC with anda weakly GC with polara weaklycolumn.polar The column.combination The of combination GC and UHPSFC, of GC and which UHPSFC, is the fastest which of is the fastesttested methods, of the tested seems methods, to be ideal seems [29]. to be ideal [29]. The firstfirst enantioseparationenantioseparation of cathinone derivativesderivatives by capillary electrophoresis (CE) was performed byby MohrMohr etet al. in 2012 using sulfated β-cyclodextrin-cyclodextrin as a chiral selector [30]. [30]. As As with with HPLC, HPLC, CE-UV andand CE-MS CE-MS techniques techniques are usedare used [31– 33[31–33].]. For example, For example, to study to the study incorporation the incorporation of cathinones of intocathinones hair, a into CE methodhair, a CE was method developed was indeveloped which extraction in which from extraction hair at from an elevated hair at temperaturean elevated andtemperature pressure and into pressure ammonium into hydroxide ammonium solution hydroxid wase first solution performed. was first Subsequently, performed. theSubsequently, extract was concentratedthe extract was on aconcentrated solid phase thaton a was solid part phase of the that CE capillarywas part (inline of the couplingCE capillary of SPE-CE), (inline andcoupling analysis of wasSPE-CE), performed and analysis using various was performed cyclodextrins using as various chiral selectorscyclodextrins [34]. as chiral selectors [34]. Mephedrone is referred to as a catecholaminecatecholamine reuptakereuptake inhibitor [35–37], [35–37], but it also positively aaffectsffects the release of catecholamines into into the the synapt synapticic cleft cleft [13,38–41]. [13,38–41]. Theref Therefore,ore, it itseems seems to to have have a amixed mixed effecteffect [42–44]. [42–44 ].In In both both cases, cases, the the result result is isan an increase increase in inthe the concentration concentration of ofcatecholamines catecholamines in inthe the synaptic synaptic cleft, cleft, resulting resulting in in the the typical typical acti actionon of psychostimulants. Acute Acute intoxication with mephedrone, usually in combination with other drugs and alcohol, has already