Conformational enantiomerism of bilirubin and pamoic acid induced by protonated aminocyclodextrins

Abstract

The conformational enantiomerism of (4Z, 15Z)-bilirubin IXα(1) induced by protonated heptakis(6-amino-6-deoxy)-β-cyclodextrin (amino-β-CD_X) has been studied in aqueous media by means of CD spectroscopy. A bisignate CD Cotton effect suggests that the dianion of 1 associated with protonated amino-β-CD_X selectively takes a conformation with (P)-helicity. The results clearly indicate that the electrostatic binding between the CO₂^– groups of 1 and the NH₃⁺ groups of amino-β-CD_X and the simultaneous inclusion of a dipyrrinone moiety of 1 into the chiral CD_X cavity are essential for the conformational enantiomerism of 1. This has also been applied to the amino-γ-CD_X-induced conformational enantiomerism of pamoic acid.