Fast atom bombardment mass spectrometry as a tool for the rapid determination of enantioselective binding of methylated cyclodextrins

The first FABMS study of the enantioselectivity shown during complex formation between per-methylated cyclodextrins and pairs of enantiomeric guest molecules is described. The 1:1 mixtures of the cyclodextrins, both α- and β-, with the guests, the methyl esters of the amino acids tryptophan and phenylalanine, were studied in a 100:50:1 glycerol-thioglycerol-trifluoro-acetic acid matrix. The uncomplexed cyclodextrin peaks were then used as internal standards to determine the preference of the cavity for one or other of the enantiomers. A clear trend for the preferential binding, greater than 5:1 in each case, of the d-enantiomers of the amino acid esters was observed in agreement with literature 1H NMR experiments. This methodology provides a rapid route to assessing the enantioselectivity shown by the widely used cyclodextrins towards pairs of enantiomeric guests.