Quinine: an inexpensive chiral solvating agent for the determination of enantiomeric composition of binaphthyl derivatives and alkylarylcarbinols by NMR spectroscopy

Diastereoisomer‐Selective Inclusion Complexation of Cinchona Alkaloids with a Modified β‐Cyclodextrin: Fluorescent Behavior Enhanced by Chiral‐Tether Binding. Short Communication

“…We observed significant fluorescence-intensity enhancements of quinine (2) and quinidine (3) upon complexation with 1 (see Fig. 1), but little increase in the fluorescence of cinchonine (4) and cinchonidine (5), which entirely contrasts the fluorescence quenching of cinchonaalkaloid sulfates upon addition of (À)-(R)-2-aminobutan-1-ol in control experiments. Different results had been obtained with both native b-CD and bridged bis(b-CD), as reported previously [12] .…”

Autoaggregation phenomena in quinine solutions

“…We carried out the relaxation rate measurements on two solutions, one 0.17 M and the other 3. 4 mM, and obtained the data reported in Table 5. The distance r12 = 2.43 A was used to assess the correlation times of the monomer and the dimer, which we determined to be 47.…”

Mono‐ and bis‐quinidine organocatalysts in the asymmetric methanolysis of cis‐1,2,3,6‐tetrahydrophthalic anhydride: A conformational and mechanistic NMR study

“…This fact was clearly indicative of a chiral recognition phenomenon, probably related to the ability of the Cinchona alkaloid derivatives to act as NMR chiral solvating agents toward suitable chiral substances. [41][42][43][44][45][46][54][55][56] Control experiments with rac-16 (50 mM) and either 4 or 13 (5 mM) in toluene-d 8 , confirmed this hypothesis, showing that even such a small concentration of the alkaloid derivatives was sufficient for inducing a rather large anisochrony in most of the protons of the enantiomers of 16 (e.g., Dd 5 0.011 ppm for the methoxy groups of rac-16 in the presence of 13, Fig. 8a).…”

“…This latter aspect appears particularly intriguing when one considers that the switch from the effective mono-e bis-alkaloid organocatalysts 3 and 4 to similar systems like 6-8 generally leads to a dramatic drop of the reaction enantioselectivity (13-32% ee), 17 whilst other apparently less related derivatives, like 9, may still provide excellent ee values (87-95% ee). 20,22 In consideration of our longstanding and continuing interest in the Cinchona alkaloids for supported asymmetric catalysis [32][33][34] and determination of enantiomer composition by chromatographic [35][36][37][38][39][40] and nuclear magnetic resonance (NMR) methods, [41][42][43][44][45][46] we were prompted to investigate further the molecular basis of the said catalytic process by exploiting the potential of NMR spectroscopy in the study of molecular recognition processes. In addition to the commercial anthraquinone ether 4, two alkaloid pyridazine derivatives 13 and 14 were selected for this purpose, which were recently introduced by our group within the framework of a project for the development of polymer supported organocatalysts.…”