Orthogonal Coupling for Hetero-Oligomer Synthesis

The synthesis was started from the suitably protected galactosyl fluoride 15 (a p = 1.7 1) which was glycosylated with GalNAc precursor 16 imder conditions (a) to afford 17. The stereochemical assignment was confirmed by H NMR  

Deprotection of the levulinoyl group on trisaccharide 20 by use of hydrazine acetate [23] afforded 21 (85.4%) which was then used as an acceptor for the a- 

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