Human milk oligosaccharides (HMOs) are the family of structurally distinct glycans which are present in human milk in significant quantity (5-25 g/L).HMOs are not digested by intestinal enzymes, while they play important roles as prebiotics which can stimulate the growth of healthy gut bacteria.Among various HMOs, the lacto-N-tetrasaccharide (LsTa, 5) and sialylated lacto-N-tetrasaccharide (sLsTa, 8 and 9) are the most common structures and the key intermediates for the biosynthesis of more complex fucosylated and sialylated structures.As shown in Scheme 1, a novel chemoenzymatic approach was developed for the synthesis of LsTa (5) and its sialylated derivatives (8 and 9).