The role of CH/π interaction in the stabilization of less-soluble diastereomeric salt crystals

Enantiopure 2-naphthylglycolic acid (NGA) and cis-1-aminobenz[f] indan-2-ol (ABI) were rationally designed as new resolving agents on the model of mandelic acid (MA) and cis-1-aminoindan-2-ol (AI), respectively. As expected, NGA and ABI showed superior chiral recognition ability to racemates, compared with MA and Al. In order to clarify any factors governing the chiral recognition abilities of NGA and ABI, the crystal structures of their less- and more-soluble diastereomeric salts were determined by X-ray crystallographic analyses and revealed that CH/n interactions play an intrinsic role in chiral recognitions. A theoretical investigation was also performed with the periodic ab initio method by using the X-ray crystal structures of the less-soluble salt crystals with All and ABI to find the unique properties of CH/n interaction in the crystalline state, which largely contributed to the stabilization of the crystals. (c) 2007 The Japan Chemical journal Forum and Wiley Periodicals, Inc.