Synthesis of N-acetyl-9-O-acetylneuraminic acid alpha-p-amino-phenylthioketoside and its application as ligand in the affinity chromatography of a lectin with preferential affinity to O-acetylated sialic acids.
The N-acetyl-9-O-acetylneuraminic acid-alpha-p-aminophenylthioketoside 7 was synthesized as a sialidase-stable ligand for the affinity chromatography of a lectin with preferential affinity to O-acetylated sialic acids. The thioketoside was prepared by phase-transfer-catalysed glycosidation followed by Zemplen deacetylation. Regioselective acetylation of the completely de-O-acetylated derivative was practised by two different methods. The acetylation with trimethylorthoacetate did not show the desired selectivity for hydroxyl groups; in addition to the acetylation in position 9 extensive formation of an acetimidate ester derivative with the amino-group in the aminophenyl-moiety was observed. However the esterification with N,N-dimethylacetamide dimethyl acetal resulted in an exclusive acetylation of the hydroxyl-group in position 9. After catalytic hydrogenation this ligand was immobilized both directly and by a six-carbon long spacer group to the agarose matrix. The adsorbents were applied in the affinity chromatography of the lectin and their binding capacity and selectivity compared to those of the formerly used mucin matrix. In both respects the thioketoside coupled by the spacer turned out to be a better ligand for the isolation of the lectin than the mucin.