Syntheses of chiral bishomodiazacalix[4]arenes incorporating amino acid residues: Molecular recognition for racemic ammonium ions by the macrocycles possessing tyrosine residues

Chiral bishomodiazacalix[4]arenes containing amino acid residues were prepared. The H-1 and C-13 nmr spectra indicated that the macrocycles preferably adopted a cone conformation, which suggested that the cyclophane moiety was in a chiral twisted form. Circular dichroism spectra supported the existence of the chirality of the cyclophane unit, and showed that intramolecular hydrogen bonding plays an important role in the transmission of the chirality from the amino acid residues to the cyclophane moiety. Macrocycles bearing a tyrosine residue have a pi-base cavity large enough to include the ammonium ion, and can serve as a shift reagent for the racemic ammonium ions upon complexation during a H-1 nmr analysis.