Sequence‐Controlled Helical Ladder Polymers: Impact of Stereochemical Sequence on Helical Geometry and Chiral Recognition

Abstract

ABSTRACT Amylose and cellulose possess diastereomeric repeating units and adopt distinct left‐handed 6/1‐ and sheet‐shaped 2/1‐helical structures, respectively, while their chemically‐modified derivatives display complementary chiral recognition abilities due to their inherent homochiral diastereomeric repeating units with different secondary structures. We now report a modular synthetic strategy for constructing helical ladder polymers with different sequences in which the stereochemical combination of two chiral ladder motifs dictates the helical geometry and chiral recognition function. Alternating annulation of the ( S )‐ or ( R )‐1,1′‐spirobiindane units with ( S )‐ or ( R )‐2,2′‐tethered 1,1′‐binaphthyl units afforded coil‐ and ribbon‐type diastereomeric helices along with their enantiomeric counterparts. These coil‐ and ribbon‐type diastereomeric helical ladders showed complementary chiral recognition when used as chiral stationary phases for liquid chromatography, whereas the corresponding nonhelical precursors exhibited no resolution capability. The corresponding enantiomeric helices showed reversal of the enantiomer elution order while retaining a comparable enantioseparation ability. These results establish modularly designed sequence‐controlled helical ladders as chiral platforms with programmable secondary structures and chiral functions.