Ab Initio Conformational Study of 1,2:4,5-Di-O-isopropylidene-myo-inositol

Abstract

Inositol phosphate derivatives play key roles in intracellular signal transduction. The X-ray structure of 1,2:4,5-diisopropylidene-myo-inositol is different from the conformer predicted by NMR and IR spectra. Therefore, we performed ab initio conformational study of the molecule, as a preliminary study before investigating the regioselectivity displayed by the myo-inositol toward electrophiles. The relative stabilities of four possible conformers of the molecule were investigated at various levels of ab initio theory: Hartree−Fock (HF) theory, Möller−Plesset second-order perturbation (MP2) theory, density functional theory (DFT), and self-consistent reaction field (SCRF) theory. Various basis sets were also tested. All calculations gave a consistent result which shows strong intramolecular hydrogen bonding interaction in an isolated system such as gas phase or solution. This is in agreement with NMR experiment. The frequency splitting between two OH vibrational frequencies due to the difference in the strength of the intramolecular hydrogen bonding is found to be very small (only several cm-1) in contrast to a large frequency difference to appear in the intermolecular hydrogen bonding. On the other hand, in the solid phase, the intermolecular hydrogen bonding is expected to be important due to the crystal packing effect, as shown in the X-ray structure.