Enantioselective recognition with C-3-symmetric cage-like receptors in solution and on a stationary phase

The chiral C-3-symmetric, cage-like receptors (S,S,S)-(+)-1 and (S,S,S)-(+)-2 with convergent, helically oriented amide hydrogen bonding sites have been prepared by a short, modular synthetic route. They are found to complex N-protected amino acid derivatives and, in particular, dicarboxylic acids in non-competitive solvents, Enantioselectivity is observed in the binding of N-Cbz-Glu (N-carbobenzyloxy-protected glutamic acid), and differences in stability of the diastereoisomeric complexes [Delta(Delta G) of up to 4.6 kJ mol(-1)] have been measured by H-1 NMR binding titrations in CDCl2CDCl2. The geometries of free and bound receptor (S,S,S)-(+)-1 have been analysed by computer molecular modelling. Receptor (S,S,S)-(+)-2 is covalently linked to thiol-functionalised silica gel, yielding the novel chiral stationary phase (CSP) (S,S,S)-14, In analytical HPLC (high performance liquid chromatography) runs, the new CSP is found to be effective for the optical resolution of (+/-)-1,1'-binaphthyl-2,2'-diol derivatives, but not for the separation of enantiomeric amino acid derivatives.