Stereospecific interaction of one-handed helical polycations with chiral anions

Abstract

Optically active polyamide helices were obtained by the reaction of axially dissymmetric ( R)- or ( S)-6,6′-dibromo-2,2′-diethoxy-1,1′-binaphthyl, 3,6-diaminoacridine (proflavine), and carbon monoxide using a palladium catalyst. The acridine units in the chiral backbone were protonated with chiral 10-camphorsulfonic acid. Circular dichroism measurements revealed that ( R)-(−)-camphorsulfonate anion (( R)-(−)-CSA −) is more easily incorporated into the protonated right-handed polyamide helix than ( S)-(+)-camphorsulfonate anion (( S)-(+)-CSA −) and that the left-handed cationic helix preferentially interacts with ( R)-(−)-CSA − to ( S)-(+)-CSA −.