Synthesis of the alpha-L-Araf-(1 -> 2)-beta-D-Galp-(1 -> 6)-(beta-D-Galp-(1 -> 6)-[alpha-L-Araf-(1 -> 2)]-beta-D-Galp-(1 -> 6)-D-Ga1 hexasaccharide as a possible repeating unit of the cell-cultured exudates of Echinacea purpurea arabinogalactan

For the characterization of the supposed epitope of an arabinogalactan, iso lated from the extract of the cell-cultured Echinacea purpurea. the title h exasaccharide was synthesized. The whole synthetic route was based on the 6 -O-(methoxydimethyl)methyl ether (MIP) protecting group strategy. 2-O-Benzy l-3,4-O-isopropylidene-6-O-(methoxydimethyl)methyl-beta -D-galactopyranosyl -(1 --> 6)-1,2:3.4-di-O-isopropylidene-alpha -D-galactopyranose was used to prepare the desired glycosyl donor and glycosyl acceptor both carrying a p ersistent O-benzyl group at position 2'. Reaction of the digalactose donor and the digalactose acceptor resulted in a beta-(1 --> 6)-linked galactose- containing tetrasaccharide in which OH-2' and OH-2'" were substituted with benzyl groups. Hydrogenolytic removal of the benzyl groups of the tetragala ctose compound gave the diol aglycon which was diarabinosylated in one step to furnish the protected target compound, whose deprotection led to the ti tle hexasaccharide. All of the synthesized compounds were characterized by H-1 and C-13 NMR spectra, as well as by MALDI-TOF mass-spectrometry measure ments. (C) 2001 Elsevier Science Ltd. All rights reserved.