CLICKING SUGARS ONTO SUGARS: OLIGOSACCHARIDE ANALOGS AND GLYCOCLUSTERS ON CARBOHYDRATE SCAFFOLDS - Click Chemistry in Glycoscience: New Developments and Strategies - page 103

SCHEME 5.1 General retrosynthetic click reaction.

5.2 TRIAZOLE-LINKED OLIGOSACCHARIDE ANALOGS

In order to link a carbohydrate to another carbohydrate residue, through a covalent
bond such as a 1,2,3-triazole ring, the modification of sugar backbones by function-
alization with azide and alkynes groups, respectively, is required. This strategy leads
to hybrid compounds, namely oligosaccharide mimics or analogs, with improved
chemical properties (Scheme 5.1).
Santoyo-Gonzalez group investigated the reaction of propargyl, thiopropargyl,
and aminopropargyl glycosides 1a-c (Scheme 5.2) using the organic-soluble cop-
per complexes (Ph 3 P) 3 .CuBr and (EtO) 3 P.CuI. The S- and N-containing derivatives
are valuable precursors of carbohydrate mimics with enhanced stability towards
enzymatic hydrolysis, and they allowed the study of the influence of the glycosidic
linkage in coupling, considering the electronic nature of each alkyne moiety [11].
It was observed that alkyne 1a , which supports the more electronegative
substituent, reacts well with (Ph 3 P) 3 .CuBr-N,N-diisopropylethylamine (DIPEA)

AcO

O

AcO X

AcO

AcO

AcO OAc N N

O

O

N

AcO OCH 2 CH 2 N 3

AcO XCH 2 C CH +

AcO

O

AcO OAc

OAc

AcO

AcO O

1a ,R=O
1b ,R=S
1c ,R=N(Ac)

2a

OAc

AcO

3a ,R=O
3b ,R=S
3c ,R=N(Ac)

SCHEME 5.2 Click reaction using organic-soluble copper complexes.