Stereospecific interaction of one-handed helical polycations with chiral anions

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−.