Recent advances in gold-catalyzed glycosylation - Carbohydrate Chemistry: Chemical and Biological Approaches - page 140

Recent advances in gold-catalyzed
glycosylation
Jun Luo and Qian Wan*
DOI: 10.1039/9781849739986-00140
An update on the glycosylation reactions catalyzed by gold(I) and gold(III) is provided since
2006 till recently.
1 Introduction
Many biologically important substances, such as antibodies, glycolipids,
glycoproteins, and proteoglycans, contain carbohydrate moieties. It is
well known these carbohydrate-containing natural products play very
important roles in a multitude of biological events. 1,2 In order to gain
better understanding of the nature of these biological processes, rea-
sonable amounts of pure and structurally well-defined materials are re-
quired. However, the accessibility of these glycosides or glycoconjugates
from the isolation of natural resource is quite limited. Chemical syn-
thesis is a major method to match the continuously increasing require-
ments. Since Koenigs and Knorr made the historical contribution more
than a hundred years before, enormous progress has been made in this
area. 3 Among the various newly developed glycosidation reactions, the
gold 4 mediated glycosylations have made significant progress since
2006. 5,6 The seminal work from two research groups (Yu and Hotha) has
broadened both application and the understanding of the novel re-
action. 7 In this review, we will highlight recent advances involving use of
catalytic gold complexes in glycosylation reactions from earliest discovery
to the present. Due to the limitation of space, we will mainly discuss the
development of new glycosyl donors and their substrate specificity.
2 Gold(III)-catalyzed glycosylation
2.1 Gold(III)-catalyzed glycosylation with 3-O-propargyl protected
glucal
In 2006, Hotha et al. discovered that in the presence of a catalytic amount
of AuCl 3 ,3-O-propargyl protected glucal 1 might undergo a Ferrier-like
reaction with various aglycones (aliphatic, aromatic, alicyclic, and
monosaccharide) to afford stereoselectively a-glucosides 2 (Scheme 1) in
moderate yields. This Au(III)-mediated reaction is found to be catalytic,
stereoselective, and moisture tolerant. The role of Au 3 þ is recognized as
greatly facilitating the leaving ability of the propargyl moiety through its
alkynophilicity. This recognition triggered a systematic study of the