Enantioselective complexation of carbohydrate or crown ether hosts with organic ammonium ion guests detected by FAB mass spectrometry

Article abstract of DOI:10.1021/ja00069a041

Enantioselective host-guest complexation has been demonstrated by FAB mass spectrometry. Among several carbohydrates, a modified β-mannofuranoside 6b as well as chiral crown ethers 10 and 13, differentiates a chiral ammonium ion guest such as the (1-(1-naphthyl)ethyl)ammonium ion. The relative peak intensity (RPI) method has been applied to the evaluation of such diastereomeric complex ions where the peak intensity of the target host (M)-guest (A⁺) complex ion I((M+A)⁺) is compared to that of the internal standard host (R)-guest (A⁺) ion I((R+A)⁺): the RPI value = I((M+A)⁺)/I((R+A)⁺). The present enantioselectivity is characterized by the RPI ratio value I((M+A_(R))⁺)/I((M+A_(S))⁺) in the range 1.2-1.6 (1.0 ± 0.1 nonenantioselectivity). The observed preference of the (R)-enantiomer guest is compatible with model examinations and related coloration results. With chiral crown ether 13, a close correspondence exists between the FABMS/RPI enantioselection and that of strictly related solution-phase energetics in association equilibria. The usefulness of the RPI method is also shown by comparison to the relevant equilibrium constants (NMR titration) in solution.