Easy chemo-enzymatic synthesis of human milk trisaccharides from a common selectively protected lactose building block

Three glycosyllactosides, contained in the neutral fraction of human milk o ligosaccharides, were synthesised in a simple and straightforward manner th rough a sequence based on a chemo-enzymatic approach. Lipase catalysed regi oselective 6'-O-acylation of benzyl beta-lactoside, followed by the introdu ction of an isopropylidene group and acetylation afforded, depending on the reaction conditions, compounds 4a and 4b, which allow selective access to positions 3, 3' and 6'. Glycosylation with proper donors gave trisaccharide s 6, 9 and 12.