The syntheses of novel penta-O-acetyl-N-glycoloylneuraminyl- and penta-O-acetyl-3-deoxy-D-glycero-D-galacto-2-nonulopyranosonic acid-(alpha 2----6)-D-glucosamine-4-phosphate analogues of lipid A containing sialic acid in place of 3-deoxy-D-manno-2-octulosonic acid are described. Preliminary examination of the biological activity revealed that two synthetic disaccharides showed mitogenic activities and weak antitumor activities.