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OAc
AcO
AcO
OAc
AcO
OAc
O
O
OAc
OAc
AcO
AcO
O
AcO
S
S
OAc
AcO
O
S
S
OAc
AcO
AcO
OAc
O
l
max
365 nm
Ac
AcO
SH
+
AcO
CH
2
Cl
2
O
O
O
O
O
O
O
O
DPAP (0.1 eq.)
1
(3 eq. x 4)
28
29
(78%)
SCHEME 3.7
Glycoclustering on a calixarene platform via TEC.
Given the high efficiency of TEC in the multiple hydrothiolation of the tetra-
allylated calix[4]arene
28
, we afforded the more challenging endeavor of installing
tetravalent
S
-glucoside clusters at both the calix[4]arene upper and lower rims using
the octa-allyl derivative
30
as a substrate reacting with the model sugar thiol
1
(Scheme 3.8) [21]. Also this reaction was carried out under standard conditions, that
is, irradiation at
max
365 nm in the presence of the radical initiator DPAP and using
3 eq. of
1
per allyl group of
30
. The total hydrothiolation of
30
was demonstrated by
the NMR analysis of the reaction mixture showing the absence of the signals in the
range 5.8-6.4 ppm corresponding to the alkene protons. Accordingly the octavalent
S
-glucoside cluster
31
was isolated in 67% yield corresponding to a 95% average
yield for each TEC.
Synthesis of the octavalent
S
-glucoside cluster
31
. To a solution of sugar thiol
1
(436 mg, 1.20 mmol) and calixarene
30
(37 mg, 0.05 mmol) in anhydrous CH
2
Cl
2
(1 mL) was added DPAP (31 mg, 0.12 mmol). The solution was irradiated (
max
365 nm) at room temperature for 1 hour under magnetic stirring, then concentrated.
The residue was treated with Ac
2
O (1 mL) and pyridine (1 mL) at room temperature
for 2 hours and then concentrated. The new residue was eluted from a column of
silica gel with AcOEt-cyclohexane (from 3:1 to 1:0) to give
31
(122 mg, 67%) as a
white foam; [
]
D
=−
44.7 (
c
0.7, CHCl
3
).
AcO
OAc
AcO
OAc
AcO
OAc
O
O
OAc
AcO
OAc
AcO
S
S
AcO
O
OAc
AcO
O
S
S
AcO
OAc
AcO
OAc
O
max
365 nm
Ac
AcO
l
SH
+
AcO
CH
2
Cl
2
O
O
O
O
OO
O
O
DPAP (0.1 eq.)
OAc
1
OAc
O
(3 eq. x 8)
AcO
AcO
S
S
O
OAc
30
AcO
S
S
OAc
AcO
OAc
O
AcO
O
OAc
O
Ac
OAc
AcO
OAc
AcO
(67%)
31
SCHEME 3.8
Glycoclustering at the upper and lower rims of calixarene platform via TEC.
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