ENANTIOSELECTIVE COMPLEXATION OF CARBOHYDRATE OR CROWN-ETHER HOSTS WITH ORGANIC AMMONIUM ION GUESTS DETECTED BY FAB MASS-SPECTROMETRY

Enantioselective host-guest complexation has been demonstrated by FAB mass spectrometry. Among several carbohydrates, a modified beta-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 diastereomcric 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.