Synthesis of nigero-oligosaccharides

Nigerose [alpha-D-Glcp-(1----3)-D-Glcp], nigerotriose, nigerotetraose, and nigeropentaose have been synthesized by chain elongation starting at the reducing end, from the corresponding octa-, undeca-, tetradeca-, and heptadeca-beta-D-acetates, respectively, via thioglycoside-mediated 1,2-cis coupling, using 1,2,4,6-tetra-O-acetyl-beta-D-glucopyranose as the glucosyl acceptor and methyl 2,3,4,6-tetra-O-benzyl-1-thio-beta-D-glucopyranoside, methyl 3-O-allyl-2,4,6-tri-O-benzyl-1-thio-beta-D-glucopyranoside, and methyl O-(2,3,4,6-tetra-O-benzyl-alpha-D-glucopyranosyl)-(1----3)-2,4,6-tri-O- benzyl-1-thio-beta-D-glucopyranoside as the donors.