Oxidation and metal-ion affinities of a novel cyclic tetrasaccharide

Abstract

The cyclic tetrasaccharide, cyclo-{→6)-α- d-Glc p-(1→3)-α- d-Glc p-(1→6)-α- d-Glc p-(1→3)-α- d-Glc p-(1→}, was oxidized in high yield to a dicarboxylic acid, cyclo-{→6)-α- d-Glc p-(1→3)-α- d-Glc pA-(1→6)-α- d-Glc p-(1→3)-α- d-Glc pA-(1→}. The parent and oxidized compound were then screened for the ability to form stable complexes with 20 metal cations. Ion-exchange thin-layer chromatography was utilized to survey binding in aqueous and 50% methanolic solutions. The screening identified Pb 2+, Fe 2+ and Fe 3+ as forming strong metal chelates with the oxidized cyclic tetrasaccharide. The stoichiometry of the oxidized cyclic tetrasaccharide and Pb 2+ complex was determined to be 1:1 using aqueous gel-permeation chromatography. Perturbations between the free and complexed structure were examined using NMR spectroscopy. Molecular simulations were used to identify a probable structure of oxidized cyclic tetrasaccharide complexed with Pb 2+.