The design and synthesis of novel chiral ionic liquids for testing as chiral selecting agents in GC stationary phases
Creators: name: Chifuntwe, Chewe
Publisher: name: RMIT University
Year: 2024

description: As the production of new chiral products such as drugs continually increases, the currently available CSPs are not guarantees to provide adequate enantioseparation for new products. With the increased demand from drug regulatory agencies for drug manufacturers to provide safety data by way of enantiomeric purity, there is a need for the development of more chiral selectors for application in gas chromatography (GC) or liquid chromatography (LC) stationary phases for the analysis of chiral drug products.<br>Given that GC is one of the preferred methods of chiral analysis recommended by drug regulatory agencies, it is important to have a range of GC stationary phases which possess diverse physical and chemical properties to allow researchers to conduct not only routine chiral analysis but provide a selection of stationary phases with the appropriate properties required to conduct specialised enantioselective analysis experiments.<br>Ionic liquids have been identified as good candidates for application as stationary phases in GC. Their negligible vapour pressure, good thermal stability, multiple solvation interaction and their tuneable physical and chemical properties make them ideal candidates for application in the design of new stationary phases.<br>In this work the design, synthesis, and testing of novel chiral ionic liquids (ILs), for enantioselective capability in GC stationary phases is presented. First, new chiral cis- and trans-2,4,5-triphenylimidazolinium ILs are synthesised as well as their achiral 2,4,5-triphenylimidazolium IL counter parts. Following which the asymmetrical N-derivatisation of trans-2,4,5-triphenylimidazoline with various amino acids is described, which upon alkylation with an alkylhalide served as precursors for the synthesis of novel chiral ILs. We also describe the synthesis of new asymmetrical chiral imidazolinium ILs with various side groups from simple amino acids, permitting the incorporation of various functional groups at positions 2, 3, 4, and 5 on the imidazoline moiety, allowing for the production of a wide range of imidazolinium ILs with tunable physical and chemical properties.<br>New ionic cyclodextrins (CD) were also synthesised from per-6-iodo-2,3-hydroxy-β-CD, per-6-iodo-2,3-O-acetyl-β-CD, per-6-iodo-2,3-O-acetyl-γ-CD to afford variousper-6-imidazolium-2,3-hydroxy-β-CD iodide, per-6- imidazolium-2,3-O-acetyl-β-CD iodide, and per-6-imidazolium-2,3-O-acetyl-γ-CD iodide as well as their pyridium ionic CD counterparts.<br>A selection of chiral ILs incorporated into capillary columns as chiral selectors diluted in OV-1701, and their phase polarities and their enantioselective capabilities evaluated. The resultant mixed phases remained relatively non-polar while displaying markedly altered retention behaviours for various analytes.<br>A good example of the need for a wider selection of chiral stationary phases that possess a variety of chemical properties for specialized applications was illustrated. In the study we conducted with chiral oximes undergoing dynamic molecular interconversion between their E &amp; Z isomeric forms during the chromatographicelution process on wax stationary phases. The study was conducted on wax column coupled to a chiral column to allow the sequential examination of the interconversion process and chiral resolution. Ideally the interconversion process and enantiomer resolution should be examined simultaneously, however, stationary phases with such capabilities are currently not available on the market, illustrating the need for the development of new chiral stationary phases (CSPs) for routine and specialised enantioselective analysis.<br><br>