Synthesis of the Two Monomethyl Esters of the Disaccharide 4-O-α-D-Galacturonosyl-D-galacturonic Acid and of Precursors for the Preparation of Higher Oligomers Methyl Uronated in Definite Sequences.

Abstract Methyl (α- d -galactopyranosyluronic acid)-(1→4)- d -galactopyranuronate and methyl α- d -galactopyranosyluronate-(1→4)- d -galactopyranuronic acid have been synthesized by coupling methyl (benzyl 2,3-di-O-benzyl-β- d -galactopyranosid)uronate (3) or benzyl (benzyl 2,3-di-O-benzyl-β- d -galactopyranosid)uronate (4) with benzyl (phenyl 2,3,4-tri-O-benzyl-1-thio-β- d -galactopyranosid)uronate and methyl (phenyl 2,3,4-tri-O-benzyl-1-thio-β- d -galactopyranosid)uronate, respectively, using N-iodosuccinimide and trifluoromethanesulphonic acid as promoters, followed by removal of the benzyl groups. The 4′-OH unprotected dimers benzyl (methyl 2,3-di-O-benzyl-α- d -galactopyranosyluronate)-(1→4)-(benzyl 2,3-di-O-benzyl-β- d -galactopyranosid)uronate and methyl (benzyl 2,3-di-O-benzyl-α- d -galactopyranosyluronate)-(1→4)-(benzyl 2,3-di-O-benzyl-β- d -galactopyranosid)uronate were prepared from methyl (phenyl 2,3-di-O-benzyl-1-thio-4-O-trimethylsilyl-β- d -galactopyranosid)uronate and benzyl (phenyl 2,3-di-O-benzyl-1-thio-4-O-trimethylsilyl-β- d -galactopyranosid)uronate and acceptors 4 or 3, respectively. These compounds have been designed to serve as precursors for the preparation of higher-membered d -galacturonic acid oligomers methyl esterified in definite positions.