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.