Synthesis of the Pentasaccharide Repeating Unit Related to the Exopolysaccharide from Lactobacillus plantarum C88 in the Form of its 2‐Aminoethyl Glycoside

Abstract

AbstractChemical synthesis of the pentasaccharide, β‐D‐Galp‐(1→6)‐α‐D‐Galp‐3‐O‐(β‐D‐Glcp)‐(1→2)‐α‐D‐Glcp‐(1→3)‐β‐D‐Glcp, is reported by following a convenient [2+2+1] strategy. Two disaccharides α‐D‐Galp‐(1→3)‐β‐D‐Glcp and α‐D‐Galp‐(1→6)‐β‐D‐Galp were synthesized from commercially available monosaccharides through rational protecting group manipulations and coupled to make a tetrasaccharide. The last Glc unit was coupled with the tetrasaccharide to furnish the target pentasaccharide. Stereoselective glycosylations were achieved by the activation of thioglycosides using N‐iodosuccinimide and H2SO4‐silica or activation of trichloroacetimidate using H2SO4‐silica alone. Finally, global deprotection furnished the target molecule. The target pentasaccharide has been synthesized in the form of its 2‐aminoethyl glycoside to facilitate further glycoconjugate formation using the terminal free amine.