Mild and Highly α‐Selective O‐Sialylation Method Based on Pre‐Activation: Access to Gangliosides Hp‐s1, DSG‐A, and Their Analogues

An efficient method for α‐selective sialylation, based on a pre‐activated 5‐N,4‐O‐carbamate thiosialoside donor using p‐TolSCl/AgOTf as reagents, is described. The strategy is further expanded to a range of sugars. A mechanism is proposed and validated using experimental evidence. The utility of the method is demonstrated by the total synthesis of gangliosides Hp‐s1 1, DSG‐A 2 and their analogues, 2 a–2 c. The neuritogenic activity of the final compounds is determined on SH‐SY5Y cells