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In-Depth Information
N
3
N
3
O
O
O
OH
HO
HO
O
HO
O
O
HO
N
3
O
N
3
N
3
O
O
22
HO
OH
OH
O
HO
O
O
HO
OH
7
O
OH
HO
OH
N
3
22
O
O
O
HO
O
2
S
N
3
O
N
3
Sugar
O
Sugar
O
23
NMe
2
(EtO)
3
P·CuI, DMF
90 °C, MW
O
Sugar
O
Sugar
O
Dansyl
N
N
N
N
N
N
N
N
N
O
O
HO
HO
O
HO
HO
HO
O
O
7
n
HO
O
m
Sugar =
-lactosyl
(per-
O
-acetylated or fully unprotected)
β
-D-galactopyranosyl or
β
24
25
(m + n = 7)
SCHEME 6.4
Synthesis of cyclodextrin-scaffolded click glycoclusters.
glycocluster architectures to explore multivalent interactions between carbohydrates
and proteins [55], because of their nanometric three-dimensional rigid structure, com-
mercial availability, and extremely rich preparative chemistry [56]. Dondoni, Marra,
and coworkers pioneered the application of click chemistry for those channels, with
the preparation of several tetra- and octavalent glycoclusters from calix[4]arene plat-
forms [44, 57]. For instance, the sialic acid derivatives
30
-
32
, obtained by click
coupling of the polyazides
26
-
28
with alkyne
29
followed by conventional deprotec-
tion (Scheme 6.5), were able to inhibit the viral infectivity by BK and influenza A
viruses at submillimolar concentrations [57].
The possibility to fix the cone, the partial cone, and the 1,3-alternate conforma-
tion in calix[4]arenes bearing
tert
-butyl substituents at C-4 and propargyl groups
at C-1 in the aromatic rings (
33
-
35
) was exploited by Vidal and coworkers for the
preparation of a library of conformationally locked click glycoclusters differing in
valency and topology [45, 58] (Fig. 6.2). Tetravalent galactosylated clusters bearing
galactopyranosyl residues at both faces of the calixarene platform were found to
be superior as ligands for the galactose-binding lectin PA-IL from the opportunis-
tic bacteria
Pseudomonas aeruginosa
as compared with compounds with the same
valency, but with monofacially oriented substituents [58]. In a recent report, Field and
coworkers encountered the reverse situation for calix[4]arene-centered tetralactosyl
click clusters when assayed for their tripanocidal activity, with monofacially oriented
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