An efficient and practical synthesis of beta-(1 --> 3)-linked xylooligosaccharides

A facile and practical method was developed for the synthesis of beta-(1 --> 3)-linked xylooligosaccharides. Dibezoylation of allyl alpha-D-xylopyranoside (1) afforded 2,4-dibenzoate 6 as the major product. Chloroacetylation of 6, followed by deallylation and trichloroacetimidation, gave a 1:3 alpha/beta imidate (10 and 11) mixture. Coupling of the imidate mixture with 6 gave a disaccharide 13, whose dechloroacetylation afforded the disaccharide acceptor 16. Condensation of perbenzoylated xylosyl alpha/beta imidate (7 and 8) mixture with 6 gave the disaccharide 12. Deallylation of 12, followed by trichloroacetimidation, furnished the disaccharide donor as a 1:1 alpha/beta mixture. Coupling of the disaccharide donor mixture with the disaccharide acceptor 16 yielded the tetrasaccharide 17. Reiteration of deallylation and trichloroacetimidation transformed 17 to the tetrasaccharide donor mixture. Condensation of the tetrasaccharide donor mixture with the acceptor 16 gave the hexasaccharide 21. Debenzoylation with saturated ammonia-methanol afforded beta-(1 --> 3)-linked allyl xylotetraoside and xylohexaoside.