Synthesis of β-d-Glcp-(1→3)-[β-d-Glcp-(1→6)]-β-d-Glcp-(1→3)-β-d-Glcp-(1→6)-[β-d-Galp-(1→4)-β-d-Glcp-(1→3)]-β-d-GlcpOLauryl, an oligosaccharide with anti-tumor activity