Characteristic conformations and molecular packings in crystal structures of diastereomeric esters prepared from (S)-2-methoxy-2-(1-naphthyl)propanoic acid

The crystal structures of the diastereomeric esters prepared from (S)-2-methoxy-2-(1-naphthyl)propanoic acid [(S)-M alpha NP acid] and (R)-1-octen-3-ol or (S)-beta-ionol were analyzed using X-ray crystallography. The conformation of the M alpha NP moiety determined from NMR analyses was observed in the crystals. In these esters, the larger, more hydrophobic alcohol substituents were coupled and matched in length with the 1-naphthyl groups. The intra- and intermolecular CH/pi interactions bridged the larger alcohol substituents and the 1-naphthyl groups. These crystal structures suggest that the CH/pi interaction is a key function of chiral resolving agents for enantioresolution. The twisted s-cis conformation was observed at the conjugated double bonds of the beta-ionol ester. Thus, M alpha NP acid is useful in clarifying the stereochemistry and conformations of biofunctional molecules. Normal-phase HPLC separation of the diastereomeric MaNP esters is also discussed. (C) 2008 Elsevier Ltd. All rights reserved.