Synthetic mucin fragments: 2-(p-trifluoroacetamidophenyl) ethyl 2-acetamido-6-O-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-2-deoxy-3-O-(β-d-galactopyranosyl)-α-d-galactopyranoside and 2-(p-trifluoroacetamidophenyl) ethyl 2-acetamido-6-O-[2-acetamido-2-deoxy-4-O-(β-d-galactopyranosyl)-β-d-glucopyranosy