Thexyldimethylsilyl 4,6-O-benzylidene-2-deoxy-2-trichloroethoxycarbonylamino-β-D- glucopyranoside (4), having the 3-hydroxy group unprotected, is a versatile starting material for the synthesis of glucosamine containing oligosaccharides. Thus, reaction with galactosyl donor5or fucosyl donor6afforded the desired β(1-3)- and α(1-3)-linked disaccharides7and8, respectively, in high yields. Reductive opening of the benzylidene moieties in7and8gave access to the 4-hydroxy groups in9and10. Ensuing fucosylation of9or galactosylation of10led to Lewis A (Lea) and Lewis X (Lex) trisaccharide building blocks13and14, respectively. Their transformation into glycosyl donors19and20and subsequent reaction with 3b-O-unprotected lactose derivative23as acceptor furnished the Lea−and Lexpentasaccharide precursors24and25. Exchange of theN-trichloroethoxycarbonyl group for anN-acetyl group and removal of theO-benzyl andO-acetyl protective groups afforded the desired Lea−and Lex−pentasaccharides1and2.