Reversible derivatization of sugars with carbobenzyloxy groups and use of the derivatives in solution-phase enzymatic oligosaccharide synthesis

Simple protocols for attaching and detaching carbobenzyloxy (Cbz) groups at the reducing end of sugars was developed. Briefly, lactose was converted into its glycosylamine, which was then acylated with carbobenzyloxy chloride in high overall yield. The obtained lactose Cbz derivative was used in sequential glycosylations using glycosyltransferases and nucleotide sugars in aqueous buffers. Isolation of the reaction products after each step was by simple C-18 solid-phase extraction. The Cbz group was removed by catalytic hydrogenolysis or catalytic transfer hydrogenation followed by in situ glycosylamine hydrolysis. In this way, a trisaccharide (GlcNAc-lactose), a human milk tetrasaccharide (LNnT), and a human milk pentasaccharide (LNFPIII) were prepared in a simple and efficient way.