MOLECULAR RECOGNITION STUDY ON A SUPRAMOLECULAR SYSTEM .10. INCLUSIONCOMPLEXATION OF MODIFIED BETA-CYCLODEXTRINS WITH AMINO-ACIDS - ENHANCED ENANTIOSELECTIVITY FOR L D-LEUCINE/

The novel beta-cyclodextrin (beta-CD) derivatives bearing a m-toluidin yl or (9-fluorenyl)alkylamino moiety have been synthesized by a conven ient method in 45% and 66% yields, respectively. The stability constan ts (K-s) and Gibbs free energy changes (-Delta G) for inclusion comple xation of mono-[6-(m-toluidinyl)-6- deoxy]-beta-cyclodextrin 1 and 9-f luorenyl)alkylamino]-6-deoxy]-beta-cyclodextrin 2 with various L/D-ami no acids have been examined by the fluorescence spectrum method in buf fered aqueous solution (pH = 7.20) at 20-23 degrees C. The modified be ta-cyclodextrins, possessing a toluidinyl or fluorenyl moiety as fluor escent probe, can recognize not only the size and shape but also the c hirality of L/D-amino acids, giving fairly good enantioselectivity up to 33 for L/D-leucine. beta-Cyclodextrin derivative 1 gave the highest K-s far L-leucine and the lowest for D-leucine among the amino acid s eries, eventually showing the highest enantioselectivity for L/D-amino acids. The molecular recognition ability and enantioselectivity for a mino acids of the modified beta-cyclodextrins 1 and 2 are discussed fr om the viewpoint of the size/shape-fit relationship between the host c avity and the guest molecules.