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)-MαNP acid] and (R)-1-octen-3-ol or (S)-β-ionol were analyzed using X-ray crystallography. The conformation of the MαNP 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/π interactions bridged the larger alcohol substituents and the 1-naphthyl groups. These crystal structures suggest that the CH/π 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 β-ionol ester. Thus, MαNP acid is useful in clarifying the stereochemistry and conformations of biofunctional molecules. Normal-phase HPLC separation of the diastereomeric MαNP esters is also discussed.

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