Diastereoisomer-Selective Inclusion Complexation of Cinchona Alkaloids with a Modified beta-Cyclodextrin:Fluorescent Behavior Enhanced by Chiral-Tether Binding

摘要

The molecular 1:1 complexation of cinchona alkaloids by mono(6-deoxy-6-([(R)-l-(hydroxymethyl)pro-pyl]amino))-beta-cyclodextrin(1)in aqueous solution has been investigated by 2D-NMR,fluorescence titration,and fluorescence-lifetime experiments.Generally,with 1 as the host,in contrast to beta-cyclodextrin proper,strong binding of quinine(2;K_a=84200 m~(-1))and quinidine(3;K_a=27300 M~(-1))at pH 6.8 was observed,as monitored by an increase in fluorescence intensity,with a fair degree of diastereoisomer discrimination(ca.3:1).To rationalize these results,two possible cooperative complexation modes,including specific H-bonding interactions to the chiral tether of the cyclodextrin portion,are proposed.