Observations on chemical and enzymatic approaches to α-2,3-sialylated octyl β-lactoside

A comparison of chemical and chemo-enzymatic syntheses of α-2,3-sialylated octyl lactoside is reported. The chemical approach, starting from lactose and sialic acid, required 14 steps and proceeded in 5% overall yield; poor α-selectivity in the sialylation step necessitated a difficult and low yielding separation of anomers. A chemoenzymatic approach, employing recombinant Trypanosoma cruzi trans-sialidase to effect the key sialylation reaction, required 10 steps and gave a similar overall yield. Whereas the chemo-enzymatic synthesis required only three chromatographic purification steps overall, the chemical synthesis required at least nine.