High-Performance Liquid Chromatographic Resolution of Neutral and Cationic Hetero[6]Helicenes

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• 作者：Geraldine M. Labrador ; Johann Bosson ; Zachary S. Breitbach ; Yeeun Lim ; Eric R. Francotte ; Rocchina Sabia ; Claudio Villani ; Daniel W. Armstrong and Jé ; rô ; me Lacour
• 关键词：carbenium ions ; CSP-HPLC resolution ; helical conformations ; racemization barriers ; single enantiomers
• 刊名：Chirality
• 出版年：2016
• 出版时间：April 2016
• 年：2016
• 卷：28
• 期：4
• 页码：282-289
• 全文大小：893K
• ISSN：1520-636X

文摘

Cationic hetero[6]helicenes mlns="" xmlns:w="http://www.wiley.com/namespaces/wiley" id="chir22579-eo-0001">mol">1⁺, mlns="" xmlns:w="http://www.wiley.com/namespaces/wiley" id="chir22579-eo-0002">mol">2⁺ and mlns="" xmlns:w="http://www.wiley.com/namespaces/wiley" id="chir22579-eo-0003">mol">3⁺ have been recently disclosed. Herein we report on their enantiomeric separation using high-performance m6">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 mlns="" xmlns:w="http://www.wiley.com/namespaces/wiley" id="chir22579-eo-0007">mol">1-H, mlns="" xmlns:w="http://www.wiley.com/namespaces/wiley" id="chir22579-eo-0008">mol">2-H, and mlns="" xmlns:w="http://www.wiley.com/namespaces/wiley" id="chir22579-eo-0009">mol">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 mol">1⁺, mol">2⁺, and mol">3⁺ was measured. For each replacement of an oxygen atom by an amino group, the m4">racemization barrier increases significantly (Δm>Gm>^‡ = 29.8, 36.3 and >37 kcal mol^-1 for mol">1⁺, mol">2⁺, and mol">3⁺ respectively). m>Chirality 28:282–289, 2016m>.