Journal Highlight: High-performance liquid chromatographic resolution of neutral and cationic hetero[6]helicenes

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  • Published: Apr 25, 2016
  • Author: separationsNOW
  • Channels: HPLC
thumbnail image: Journal Highlight: High-performance liquid chromatographic resolution of neutral and cationic hetero[6]helicenes
The enantiomeric separation of recently synthesised cationic hetero[6]helicenes has been accomplished by HPLC with different types of columns.

The enantiomeric separation of recently synthesised cationic hetero[6]helicenes has been accomplished by HPLC with different types of columns.

Chirality, 2016, 28, 282-289
Geraldine M. Labrador, Johann Bosson, Zachary S. Breitbach, Yeeun Lim, Eric R. Francotte, Rocchina Sabia, Claudio Villani, Daniel W. Armstrong and Jérôme Lacour

Abstract: Cationic hetero[6]helicenes 1+, 2+ and 3+ have been recently disclosed. Herein we report on their enantiomeric separation using high-performance liquid chromatography. Separation of the antipodes can be achieved in preparative scale on neutral adducts with Chiralcel OD-I or Chiralpak ID CSP. Selectivity factors of 1.90, 1.67, and 1.96 were obtained for 1-H, 2-H, and 3-H, respectively. Separation can also be performed on the carbenium ions on regular Chiralpak IA CSP using water-containing eluents, thus allowing for enantiomeric purity determinations in aqueous environments. Resolution of neutral and cationic helicenes is also achieved on more recently developed LARIHC columns. The versatility of the cyclofructan phases allows for baseline separations for both cases and their loading capabilities are demonstrated. Finally, the configurational stability of 1+, 2+, and 3+ was measured. For each replacement of an oxygen atom by an amino group, the racemization barrier increases significantly (ΔG‡ = 29.8, 36.3 and >37 kcal mol-1 for 1+, 2+, and 3+ respectively).

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