A series of indolocarbazole-pyridine (IP) hybrid foldamers containing chiral residues at multiple different positions were prepared to reveal the matched and mismatched phenomena of local stereocenters on the induction of helical bias. These foldamers adopted stable helical conformations, thus affording well-resolved separate sets of 1H NMR signals for right- (P) and left-handed (M) helices in water saturated organic solvents such as toluene and dichloromethane. The ratios of P- and M-helices were determined by integrating the 1H NMR signals, in combination with the molar circular dichroism (Δ ϵ) and optical rotation ([α]D) values. The degree of helical bias was larger in the IP foldamer bearing chiral residues at the termini relative to those at the pyridine side chains, but the preferred helix orientation was opposite to each other. Foldamers 5(SS)t(SSS)py and 6(RR)t(SSS)py with chiral residues at five different positions demonstrated the matched and mismatched phenomena of local stereocenters in 6(RR)t(SSS)py and 5(SS)t(SSS)py, respectively.
Bibliographical noteFunding Information:
This study was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MEST) (2015R1A2A1A10053607).
© 2018 American Chemical Society.
All Science Journal Classification (ASJC) codes
- Organic Chemistry