The meso Helix: Symmetry and Symmetry-Breaking in Dynamic Oligourea Foldamers with Reversible Hydrogen-Bond Polarity

Romina Wechsel, James Raftery, Dominique Cavagnat, Gilles Guichard, Jonathan Clayden*

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)

19 Citations (Scopus)
215 Downloads (Pure)

Abstract

Oligoureas (up to n=6) of meso cyclohexane-1,2-diamine were synthesized by chain extension with an enzymatically desymmetrized monomer 2. Despite being achiral, the meso oligomers adopt chiral canonical 2.5-helical conformations, the equally populated enantiomeric screw-sense conformers of which are in slow exchange on the NMR timescale, with a barrier to screw-sense inversion of about 70kJmol-1. Screw-sense inversion in these helical foldamers is coupled with cyclohexane ring-flipping, and results in a reversal of the directionality of the hydrogen bonding in the helix. The termini of the meso oligomers are enantiotopic, and desymmetrized analogues of the oligoureas with differentially and enantioselectively protected termini display moderate screw-sense preferences. A screw-sense preference may furthermore be induced in the achiral, meso oligoureas by formation of a 1:1 hydrogen-bonded complex with the carboxylate anion of Boc-d-proline. The meso oligoureas are the first examples of hydrogen-bonded foldamers with reversible hydrogen-bond directionality.

Original languageEnglish
Pages (from-to)9657-9661
Number of pages5
JournalAngewandte Chemie - International Edition
Volume55
Issue number33
Early online date14 Jun 2016
DOIs
Publication statusPublished - 8 Aug 2016

Keywords

  • Chirality
  • Foldamers
  • Helices
  • NMR spectroscopy
  • Structure elucidation

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