Development of a Karplus equation for 3JCOCH in ester-functionalized glucopyranoses and methylglucuronate.

Abstract

Empirical Karplus equations are very useful in the conformational analysis of flexible molecules, especially with regards to carbohydrates. The C(sp 2 )OCH dihedral angle of ester-functionalized carbohydrates, however, is not well described by widely used Karplus equations for COCH dihedral angles, because they are based on C(sp 3 )OCH data. Herein, we propose a three parameter Karplus equation of the form 3 JCOCH = 5.18 cos 2 (*) -1.42 cos(*) + 1.05 on the basis of quantum mechanics computations for 6-O-acetyl-α/ß-D-glucopyranose. The equation gives satisfactory agreement between experimentally determined 3 JCH values and those back calculated from MD simulations using the GLYCAM06 forcefield for a set of acetylated glucoses and methyl glucuronate.