¹H NMR studies of enantioselective host–guest complexation by modified β-cyclodextrins and their europium(III) complexes

Abstract

The enantioselectivity of mono-substituted β-cyclodextrins 6A-[bis(carboxylatomethyl)amino]-6A-deoxy-β-cyclodextrin, 6βCDidaH2, (2AS,3AS)-3A-[bis(carboxylatomethyl)amino]-3A-deoxy-β-cyclodextrin, 3βCDidaH2, 6A-[tris(carboxylatomethyl)(2-aminoethyl)amino]-6A-deoxy-β-cyclodextrin, 6βCDedtaH3, and their Eu3+ complexes in the formation of host-guest complexes with six enantiomeric guests in D2O have been studied by 1H NMR 600 MHz spectroscopy. The guests are d/l-tryptophanate, d/l-Trp-, d/l-4hydroxyphenylglycinate, d/l-4HOPhg-, d/l-histidinate, d/l-His-, d/l-pheniramine, d/l-Phm/d/l-PhmH+, d/l-phenylglycinate, d/l-Phg-, and d/l-β-phenylserinate, d/l-βPhs-. Enantioselective host-guest complexation occurs between [Eu(3βCDida)]+, [Eu(6βCDida)]+, and [Eu(6βCDedta)] and d/l-Trp-, [Eu(3βCDida)]+ and [Eu(6βCDida)]+ and d/l-4HOPhg-, and βCD, 3βCDida2-, 6βCDida2-, 6βCDedta3-, [Eu(3βCDida)]+, [Eu(6βCDida)]+, and [Eu(6βCDedta)] and d/l-Phm/d/l-PhmH+. While host-guest complexation occurs for d/l-His- and d/l-Phg-, no enantioselectivity is apparent. Host-guest complexation occurs in the d/l-βPhs- systems but their spectra are too complex for reliable analysis. The preparation of 3βCDidaH2 and 6βCDedtaH3 and the determination of their pKas are also reported. © 2007 Elsevier Ltd. All rights reserved.