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

The enantioselectivity of mono-substituted β-cyclodextrins 6^A-[bis(carboxylatomethyl)amino]-6^A-deoxy-β-cyclodextrin, 6βCDidaH₂, (2^AS,3^AS)-3^A-[bis(carboxylatomethyl)amino]-3^A-deoxy-β-cyclodextrin, 3βCDidaH₂, 6^A-[tris(carboxylatomethyl)(2-aminoethyl)amino]-6^A-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, 3βCDida^2-, 6βCDida^2-, 6βCDedta^3-, [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 pK_as are also reported.