A P-helical quinoline oligoamide foldamer was grafted on silica and applied as an HPLC stationary phase for chiral separation. The P-handedness of the quinoline oligoamide foldamer was induced by a (1S)-camphanyl group, which was introduced at the N-terminus of a tetrameric quinoline oligoamide foldamer (Cmp-Q 4 ). To immobilize the foldamer on porous silica particles, a trimethoxysilyl group was introduced at the opposing end of the foldamer. Elemental analysis indicated that the amount of foldamer on the silica surface was 0.57 μmol/m 2 . Circular dichroism and vibrational CD spectra of Cmp-Q 4 and Cmp-Q 4 -immobilized silica (Sil-Q 4 -Cmp) suggested that the helical structure of Cmp-Q 4 was altered on the silica surface whilst retaining a chiral structure. The chiral recognition ability of Sil-Q 4 -Cmp was evaluated with various aromatic enantiomers. Sil-Q 4 -Cmp showed enantio-selectivity for axially chiral molecules (e.g., α Trigger's base = 1.26 and α Binaphthol = 1.07). Sil-Q 4 -Cmp showed remarkable recognition of helical octameric quinoline oligoamides with isobutoxy and triethylene glycol side chains (α = 10.35 and 14.98, respectively). In contrast, an (1S)-camphanyl group-immobilized porous silica showed no chiral recognition for any enantiomers tested in this study. To elucidate the chiral separation mechanism of Sil-Q 4 -Cmp, thermodynamic parameters were calculated using van't Hoff plots. HPLC results and thermodynamic parameters suggested that the chiral recognition of Sil-Q 4 -Cmp is based on the helical structure of Cmp-Q 4 and other thermally dependent interactions such as hydrophobic effects associated with aromatic stacking. This work represents the first known application of aromatic foldamers in chiral separation.
Noguchi, H., Takafuji, M., Maurizot, V., Huc, I., & Ihara, H. (2016). Chiral separation by a terminal chirality triggered P-helical quinoline oligoamide foldamer. Journal of Chromatography A, 1437, 88–94. https://doi.org/10.1016/j.chroma.2016.01.059