Enantioselective binding of tryptophan by .alpha.-cyclodextrin

1 H and 13 C NMR studies of racemic and optically pure tryptophan binding with α-cyclodextrin are carried out to explain chiral recognition in this guest-host system. The changes in chemical shifts, coupling constants, and relaxation times for the R enantiomer are larger than for S upon binding, and differential changes of R vs S in the bound state are larger for the more tightly bound R enantiomer. An intermolecular NOE between guest and host places the indole ring near the secondary hydroxyl rim of the cyclodextrin for both enantiomers, suggesting similar modes of binding