The chemical reactions and pathways resulting in the formation of a Lewis x epitope, a trisaccharide (beta-D-galactosyl-(1,4)--N-acetyl-beta-D-glucosamine) expressed on several glycolipids, glycoproteins, and proteoglycans of the nervous system. The related Lewis x epitope is formed by alpha(1,3) fucosylation of the N-acetylglucosaminyl residue of a type 2 histo-blood group antigen precursor disaccharide.
sialyl-Lewis X biosynthetic process