Enzymic transfer of 6-modified D-galactosyl residues : synthesis of biantennary penta-and hepta-saccharides having two 6-deoxy-D-galactose residues at the nonreducing end and evaluation of 6-deoxy-D-galactosyl transfer to glycoprotein using bovine β- (1-4) -galactosyltransferase and UDP-6-deoxy-D-g