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G
G
O
O
O
CuSO
4
N
a ascorba
te
N
O
OH
HO
OH
N
N
N
G
O
N
O
O
O
N
O
O
+
O
O
O
HO
OMe
HO
N
3
O
O
H
2
O
R
OMe
O
HO
O
N
N
N
G
153
154
R = OH
R = NHAc
O
152
N
N
N
155
156
G = Lac
G = LacNAc
SCHEME 5.33
Galactose-centered multilactosides.
Carbohydrate-centered glycoclusters were prepared from methyl-2,3,4,6-tetra-O-
propargyl
-D-galactopyranoside
152
and 2-azidoethyl lactoside
153
or 2-azidoethyl
N-acetyllactosamine glycoside
154
(83% and 88% for
155
and
156
, respectively)
(Scheme 5.33). The glycoclusters showed a 400-fold enhanced binding affinity to the
plant lectin ricinus communis agglutinin I (RCA120) (minimum inhibition concen-
tration 50
M) relative to free lactose (20 mM) [56b].
Santoyo-Gonzalez and coworkers [58] reported the synthesis of multivalent neo-
glycoconjugates by clicking Man and Glc derivatives, in a sequential process, on
monosaccharide and disaccharide scaffolds (
157-159
) (Scheme 5.34). The valency
of the final product (
160
-
162
) as well as the
-Man/Glc ratio, could be determined
by the number of alkyne and chloride substituents (as precursors of azides) on the
scaffold. Also, this strategy allowed the introduction of linkers of different lengths
(Scheme 5.35). The click reactions were performed using (EtO)
3
P.Cu(I) in toluene
(70-90% yield).
The influence of the substitution pattern and the distance between sugar residues,
as key features in multivalent interactions, was studied by evaluating the binding
affinities of the products to Concanavalin A (Con A) lectin. Higher relative potencies
per sugar moiety were observed, in both homo and hetero neoglycoconjugates, when
the sugar residues were not directly connected to the 1,2,3-triazole ring through their
anomeric positions.
In our laboratory, we developed a procedure to carry out the regioselective
polyazidation of fully unprotected sugars (D-glucose, maltose, and maltotriose) using
Cl
Cl
O
O
Cl
O
O
2
2
Cl
2
O
Cl
O
O
O
O
O
2
O
2
O
O
O
Cl
O
2
O
OMe
OMe
Cl
2
O
O
O
157
159
O
Cl
2
158
O
SCHEME 5.34
Mono-and disaccharide scaffolds.
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