Guilty by Dissociation: Part B: Evaluation of Supercritical Fluid Chromatography (SFC-UV) for the analysis of regioisomeric diphenidine-derived Novel Psychoactive Substances (NPS)

Guilty by dissociation: Part C: Enantiomeric separation of diphenidine-derived new psychoactive substances (NPS) by polar organic chiral high performance liquid chromatography (HPLC) on polysaccharide-based stationary phases

This study describes a simple and practical HPLC analysis for the direct enantiomeric separation of a range of 32 novel diphenidine derived psychoactive substances using a range of six polysaccharide-based chiral stationary phases employing a single generic polar organic solvent chromatographic mobile phase. Temperature was employed to optimize the chemo and enantiomeric selectivity. Baseline separation and differentiation of both the enantiomers and positional isomers (i.e., regioisomers) of the 2-, 3- and 4-methoxphenidines was achieved with the chiral selector cellulose tris(3-chloro-4-methylphenylcarbamate) coated onto silica. The latter proved to be the best of the six chiral stationary phases investigated in that it generated enantiomeric separation of 25 of the 26 monosubstituted diphenidines with resolution values > 1.5. It yielded the optimum separation for 21 of the 26 diphenidines (resolution values ranged from 2.9 - 22.4) including the 2-, 3- and 4-positional isomers of eight diphenidine derivatives. Excellent separation of all 26 monosubstituted diphenidines (i.e., resolution values > 1.5) and peak shape (i.e., typical tailing factors between 0.9 - 1.2) could be achieved by using Lux Cellulose-2 and Lux i-Amylose-3 columns. The nature of the polysaccharide-based chiral selector was demonstrated to be extremely important in determining the degree of chiral resolution. The location of the monosubstituent on the 1-phenyl ring of the diphenidine was shown to be important in promoting chiral resolution. Greater chiral discrimination was typically observed for substituents in the 4-position compared to those in the 2-position of the 1-phenyl ring. The chiral HPLC methodology displayed good chemo and enantiomeric selectivity of the mono-, di- and trisubstituted diphenidine regioisomers. Enantiomer elution order reversal was highlighted with 2-methoxphenidine enantiomers as a function of the chiral stationary phase. The (R)-enantiomer eluted before the (S)-enantiomer on cellulose-based chiral stationary phase whereas the reverse occurred with the amylose-based phases. Application of the methodology to the analysis of real-life samples of 2-methoxphenidine and diphenidine confirmed that these psychoactive substances were being traded as racemic products. Commonly used adulterants in powdered samples were shown not to interfere with the chiral analysis of 2-methoxphenidine and diphenidine.

Simultaneous and rapid analysis of chiral Danshensu and its ester derivatives by supercritical fluid chromatography

The analysis and separation of chiral compounds with wide polar range by supercritical fluid chromatography is of major importance in the process of drug development and quality control. In this work, a fast and reliable enantioselective method for the simultaneous quantitative determination of 8 DBZ-related enantiomers has been successfully developed by supercritical fluid chromatography using an amylose-based reversed-chiral stationary phase. Within less than seven minutes all target compounds could be baseline resolved, using a mobile phase comprising supercritical carbon dioxide and methanol with 0.05 % H₃PO₄. The optimum chiral stationary phase showed to be a CHIRALPAK® AD-RH column, operated at flow rate of 3.0 mL/min, back pressure of 150 bar and temperature of 40 °C. Method validation confirmed that the developed procedure was selective, linear (r² > 0.998), accurate (recovery rates: 98.02-100.02 %), and precise (intra-day: 0.05-1.98 %, inter-day: 0.08-1.98 %); the limit of detection and limit of quantification were 0.13-0.55 μg/mL and 0.37-1.68 μg/mL on column, respectively. After initial evaluation of stability according to the ICH Q1A (R2) guideline, R-DBZ showed good stability. Thus, this developed method can be used for assessing the stability of bulk DBZ samples, dosage forms of DBZ and also for monitoring the synthetic procedures of DBZ.