Syntheses of N-Glycosides by Silver-Assisted Gold Catalysis.

Synthesis of N -glycosides from stable glycosyl donors in a catalytic fashion is still challenging though they exist ubiquitously in DNA, RNA, glycoproteins, etc.   Herein, silver-assisted gold-catalyzed activation of alkynyl glycosyl carbonate donors has been identified to be versatile for the synthesis of purine and pyrimidine nucleosides, asparagine-glycosides and quinolin-2-one N -glycosides.  Thus synthesized nucleosides were subjected to the oxidation-reduction sequence for the conversion of Rib f - to Ara f - nucleosides giving access to otherwise difficult nucleosides.  Furthermore, the protocol is demonstrated to be suitable for the synthesis of 2'-modified nucleosides in a facile manner.  Direct attachment of asparagine containing dipeptide to the glucopyranose and subsequent extrapolation to afford the dipeptide disaccharide unit of chloroviruses is yet another facet of this endeavor.