The molecular structure and some properties of hydroxymatairesinol. An ab initio study

Conformations of the two diastereomers of the natural lignan hydroxymatairesinol (HMR) from Norway Spruce (Picea abies), their interactions with alkali metal cations Na+ and K+, and the mechanism and some other aspects of the dehydrogenation reaction between HMR and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) were studied computationally with molecular mechanics, semiempirical methods (AM1 and PM3), ab initio quantum chemical method at the HF level and density functional theory with the B3LYP functional, using 6-31G(d) basis set with the two latter methods. The calculations involving water as a solvent were performed employing polarized continuum model. In the gas phase and in water solution the most stable conformers of the diastereomers were found to be of almost equal energy. The study on interactions between an alkali metal cation and HMR revealed that in the energetically favourable complexes the K+ cation may act as a bridge connecting two molecules to an agglomerate and thus promote nucleation. However, in water it may be energetically more favourable to solvate the metal cations rather than form the cation-HMR complexes. The oxidative reaction of HMR by DDQ through the hydride abstraction mechanism, yielding oxomatairesinol as the major product, is kinetically and thermodynamically more favoured than the reaction yielding 7', 8'-dehydro-7-hydroxymatairesinol. The observed differences in the outcome of the reactions, where the pure epimers of HMR interact with DDQ, can be explained in terms of the stereoelectronic effects. (C) 2004 Elsevier B.V. All rights reserved.