ABSTRACT
Glycosyl azides are an important family of carbohydrate derivatives.1 They have been used as precursors of glycopeptides2 and heterocyclic N-glycosides.3 The corresponding glycosylamines, which can be obtained by reduction of the azide group, can be used as precursors to glycopolymers or hyper-branched dendrimers, after N-acryloylation.4 Furthermore, azide functionalities can be easily converted into
Experimental .......................................................................................................... 258 General Methods ............................................................................................... 258 2,3,4,6-Tetra-O-acetyl-β-d-galactopyranosyl-(1 → 4)-2,3,6-tri-O-acetyl-αd-glucopyranosyl bromide (2) ........................................................................... 258 2,3,4,6-Tetra-O-acetyl-β-d-galactopyranosyl-(1 → 4)-2,3,6-tri-O-acetyl-βd-glucopyranosyl azide (3) ............................................................................... 259
Acknowledgments ..................................................................................................260 References .............................................................................................................. 261
isothiocyanates for the synthesis of novel glycosyl intermediates.5 Recent applications of the Cu(I)-catalyzed Huisgen azide-alkyne [1,3]-dipolar cycloaddition6 have renewed interest in glycosyl azides.7,8
We present herein an efcient synthesis of hepta-O-acetyl-β-lactosyl azide 3 via phase transfer catalysis under conditions developed by our group (Scheme 31.1).9 Firstly, β-lactose octaacetate was transformed into acetobromo-α-lactose 2, using a commercially available solution of 33% HBr in AcOH. Without further purication, bromide 2 was converted under mildly basic, phase transfer catalyzed conditions into compound 310 in 88 to 93% yields in two steps. Other methods for the synthesis of glycosyl azides require strong Lewis acid-catalyzed treatment with TMSN3 for several hours11 or the use of sonication.12 These methods can be lengthy and expensive, and often provide anomeric mixtures of azides.
