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

The synthesis of N-glycosides from stable glycosyl donors in a catalytic fashion is still challenging, though they exist ubiquitously in DNA, RNA, glycoproteins, and other biological molecules. Herein, silver-assisted gold-catalyzed activation of alkynyl glycosyl carbonate donors is shown to be a versatile approach 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 Ribf- into Araf- nucleosides, giving access to nucleosides that are otherwise difficult to synthesize. Furthermore, the protocol is demonstrated to be suitable for the synthesis of 2'-modified nucleosides in a facile manner. Direct attachment of an asparagine-containing dipeptide to the glucopyranose and subsequent extrapolation to afford the dipeptide disaccharide unit of chloroviruses is yet another facet of this endeavor.

Total Synthesis of Conjugation-Ready Hyperbranched Pentasaccharide of Clavibacter phaseoli VKM Ac-2641T by [Au]/[Ag] Catalysis.

Infections by Clavibacter spp. cause an economic burden to farmers. The components present in the cell wall glycopolymers (CWGs) are important for studying the host-pathogen interactions, colonization, and infection. A pentasaccharide containing a hyperbranched Ribf-, Galf-, and Manp- has recently been identified. Herein, we describe the first total synthesis of the conjugation-ready hyperbranched pentasaccharide of C. phaseoli VKM Ac-2641T using the [Au]/[Ag]-catalyzed glycosidation chemistry of ethynylcyclohexyl carbonate glycosyl donors. The pentasaccharide was synthesized in a highly convergent fashion from readily accessible monosaccharide building blocks.