Solid phase synthesis of polylactosamine oligosaccharide

Solid phase synthesis of polylactosamine oligosaccharide was performed starting from resin supported lactose 1a,b. Glycosylation of 1a with the lactosamine unit 6 followed by delevulinoylation afforded tetrasaccharides, which were further converted into hexa- and octasaccharide and was cleaved from resin by TrBF4 in CH2Cl2 to afford 7. Ester linked 1b was converted in a similar manner into hexasaccharide that was liberated under basic conditions to give 8. Subsequent deprotection into 9 was performed in three steps.