CD-monitored enantiomeric discrimination of organic ammonium salts by chiral pyridino macrocycles

We report herein the latest results of our systematic circular dichroism (C D) studies on the enantiomeric recognition of four chiral aralkyl ammonium salts by a series of chiral and one achiral pyridino-18-crown-6 hosts. Abov e 240 nm complex formation generally resulted in a significant increase or decrease of band intensities. The effects of H-bonding and pi pi interactio n could be separated by comparing the spectral change induced by the aralky l ammonium ion with that of the achiral complexing agent butylammonium perc hlorate. Below 240 nm H-bondings alone were not found to have a significant effect upon the position and intensity of bands. Therefore definite spectr al changes in this region were interpreted as diagnostic of nir interaction . Crown hosts (S,S)-1, (S,S)-3 and (R,R)-4 (Scheme 1) showed the most strai ghtforward discriminating power. The induced CD observed in interactions of the achiral host 8 may find a wide range of analytical application for det ecting and discriminating enantiomeric aralkyl ammonium salts.