Attempts to separate (–)‐α‐thujone, (+)‐β‐thujone epimers from camphor enantiomers by enantioselective HPLC with polarimetric detection

Abstract

In a first step, 26 chiral stationary phases (CSPs) have been screened for the separation of (-)-α-thujone, (+)-β-thujone epimers and camphor enantiomers by LC. The separations were monitored by a polarimeter detector. None of these CSPs provided a noticeable resolution for camphor enantiomers. The three components of a test mixture were clearly baseline separated on Chiralpak AS-H, Chiralpak AZ-H and TCI-MBS (poly(N-alpha-(S)-methylbenzylmaleimide) coated on silica gel) in a mobile phase composed of hexane/2-PrOH (99:1 v/v). Interestingly, for a preparative application, the three CSPs produced different elution orders for the three constituents of the mixture. In a second step, it is shown that the use of online polarimetric detection constitutes an unprecedented method to reveal the occurrence and the relative content of thujone epimers and the chirality of the major camphor enantiomer in crude essential oils. A proof of concept is illustrated on crude essential oils from Rosmarinus tournefortii, Artemisia herba alba and A. arborescens, which grow in Morocco and have several traditional uses there. In a third step, pure (+)-β-thujone was quantitatively collected from A. arborescens crude oil by semi-preparative HPLC on Chiralpak AZ-H monitored by a polarimeter.

Artemisia arborescens Essential Oil Composition, Enantiomeric Distribution, and Antimicrobial Activity from Different Wild Populations from the Mediterranean Area

“…This suggests that the accessions from Algeria (Ain Sefra and Bechar) could be designated as β ‐thujone and intermediate ( β ‐thujone + camphor) chemotypes, respectively, whereas those from southern Italy as chamazulene chemotype. These results agree with those reported from several authors in which the EO of A . arborescens coming from collection sites nearby the sea showed similar β ‐thujone and chamazulene contents.…”

“…Enantiomerically pure (+)‐ β ‐thujone was previously reported by El Montassir et al. in the EO of A . arborescens from Morocco using enantioselective HPLC with polarimetric detection.…”

“…GC/MS analyses were performed on a 7890A GC system coupled to a 5975C VL mass spectrometer detector ( Agilent Technologies ) equipped with a HP‐5MS capillary column ( J&W Scientific , 30 m × 0.25 mm × 0.25 μm). Data acquisition and processing were performed using the MSD Chemstation E.01.01.335 ( Agilent ) software . A quantity of 1 μl of diluted EO (0.05 g in 1.5 ml of CH 2 Cl 2 ) was injected.…”

Isolation of the major chiral compounds from Bubonium graveolens essential oil by HPLC and absolute configuration determination by VCD

“…Chirality issues are of prime importance, since EOs could be viewed as a sustainable source of valuable optically pure compounds . High‐performance liquid chromatography (HPLC) on a chiral stationary phase (CSP) with polarimetric detection has proven useful to isolate pure enantiomers of terpenes from crude EOs without any sample pretreatment . The comparison of calculated and experimental vibrational circular dichroism (VCD) spectra is a reliable method for the determination of the absolute configuration of chiral molecules .…”

“…8 High-performance liquid chromatography (HPLC) on a chiral stationary phase (CSP) with polarimetric detection has proven useful to isolate pure enantiomers of terpenes from crude EOs without any sample pretreatment. 9 The comparison of calculated and experimental vibrational circular dichroism (VCD) spectra is a reliable method for the determination of the absolute configuration of chiral molecules. [10][11][12][13][14][15] Most VCD spectra of natural products are performed on pure isolated compounds.…”