Assessment by molecular mechanics of the preferred conformations of the sixteen C(4)–C(6) and C(4)–C(8) linked dimers of (+)-catechin and (–)-epicatechin with axial or equatorial dihydroxyphenyl substituents at C(2)

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Abstract
The molecular mechanics program MM2 has been employed for a conformational analysis of 16 dimers of (+)-catechin and/or (–)-epicatechin that have axial dihydroxyphenyl substituents at C(2). Monomer units are linked by 4α–6, 4α–8, 4β–6, and 4β–8 interflavan bonds. There is a two-fold rotation about the bond between monomer units, as has previously been shown to be the case for dimers with equatorial dihydroxyphenyl substituents at C(2). The exact value of the dihedral angle at the local minima is influenced by the stereochemistry at both C(3) and C(4) of the unit that is bonded through C(4). Heterocyclic rings occupy a range of conformations that parallel those seen when the substituents at C(2) occupy equatorial positions. Variations in the heterocyclic ring conformations are obtained by co-ordinated motion of C(2) and C(3) with respect to the mean plane of the fused atomic ring system.

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