Synthesis of the two monomethyl esters of the disaccharide 4-O-alpha-D-galacturonosyl-D-galacturonic acid and of precursors for the preparation of higher oligomers methyl uronated in definite sequences

Methyl (alpha-D-galactopyranosyluronic acid)-(1 --> 4)-D-galactopyranuronat e and methyl alpha-D-galactopyranosyluronate-(1 --> 4)-D-galactopyranuronic acid have been synthesized by coupling methyl (benzyl 2,3-di-O-benzyl-beta -D-galactopyranosid)uronate (3) or benzyl (benzyl 2,3-di-O-benzyl-beta-D-ga lactopyranosid)uro (4) with benzyl (phenyl 2,3,4-tri-0-benzyl-1-thio-beta-D -galactopyranosid)uronate and methyl (phenyl 2,3,4-tri-O-benzyl-1-thio-beta -D-galactopyranosid)uronate, respectively, using N-iodosuccinimide and trif luoromethanesulphonic acid as promoters, followed by removal of the benzyl groups. The 4'-OH unprotected dimers benzyl (methyl 2,3-di-O-benzyl-alpha-D -galactopyranosyluronate)-(1 --> 4)-(benzyl 2, 3-di-O-benzyl-beta-D-galacto pyranosid)uronate and methyl (benzyl 2, 3-di-O-benzyl-alpha-D-galactopyrano syluronate)-( 1 --> 4)-(benzyl 2,3-di-O-benzyl-beta-D-galactopyranosid)uron ate were prepared from methyl (phenyl 2,3-di-O-benzyl-1-thio-4-O-trimethyls ilyl-beta-D-galactopyranosid)uronate and benzyl (phenyl 2,3-di-O-benzyl-1-t hio-4-O-trimethylsilyl-beta-D-galactopyranosid)uronate and accepters 4 or 3 , respectively. These compounds have been designed to serve as precursors f or the preparation of higher-membered D-galacturonic acid oligomers methyl esterified in definite positions. (C) 1998 Elsevier Science Ltd. All rights reserved.