Porcine liver (2 → 3)-α-sialyltransferase: substrate specificity studies and application of the immobilized enzyme to the synthesis of various sialylated oligosaccharide sequences

In search of substrate analogues for the porcine liver β-d-Galp-(1 → 3)-d-Galp-NAc: CMP-Neu5Ac-(2 → 3′)-α-sialyltransferase, three disaccharides β-d-Gal p-(1 → 3)-β-d-Gal p-O-CH3 (5), β-d-Gal p-(1 → 3)-β-d-(2-OAc)-Gal p-O-CH3 (7) and β-d-Gal p-(1 → 3)-β-d-(2-OAc)-Gal p-O-Bn (11) were synthesized and tested with the enzyme. Disaccharide 7 turned out to be a very good substrate allowing a rapid access to the trisaccharide α-Neu5Ac-(2 → 3)-β-d-Gal p-(1 → 3)-β-d-(2-OAc)-Gal p-O-CH3 (13) on a preparative scale using the crude enzyme immobilized on cationic exchanger. Trisaccharide 13 was further exploited, first as a sialyl donor in Trypanosoma cruzi trans-sialidase catalyzed reaction and second through acetolysis reaction as a source for the synthon α-Neu5Ac-(2 → 3)-d-Gal (16).