Biomedical Engineering Reference
In-Depth Information
OBn
O
OH
OPMB
OTBDPS
TBDPSO
O
O
OH
TBDPSO
TBDPSO
O
O
STol
OBn
1. DDQ, MS 4 Å
CH
2
Cl
2
, 0°C to rt
OBz
OBz
O
O
OBn
OBn
O
O
Ara
f
22
domain of
microbacterial AG
2. IDCP, CH
2
Cl
2
, rt
3. DDQ, MeCN, H
2
O
OPMP
OBn
OBn
OPMP
O
O
23%
O
O
TBDPSO
TBDPSO
O
OH
OH
OTBDPS
O
OBn
O
OBn
DDQ
IDCP
PMP
O
TBDPSO
O
O
OTBDPS
O
TolS
OBn
SCHEME 12.49
Synthesis of the Araf
22
domain of the
M. tuberculosis
arabinoglycan
via IAD.
b
-arabinofuranosides of
M. tubercolosis
arabinan [132]. The reasons for this selec-
tivity remain unclear.
12.7.3. Intramolecular Aglycon Delivery
Intramolecular aglycon delivery [31] is a strategy guaranteeing the exclusive for-
mation of 1,2-
cis
-linkages regio- and stereoselectively via a tethered intermediate
under kinetic control, regardless of the structure of the acceptor (see above). Prandi
and coworkers applied the technique to the synthesis of an arabinan domain
(Scheme 12.49) [133]. Thus, adapting the methodology of Ito and Ogawa [32a],
the reaction of a 2-
O-p
-methoxybenzyl-protected donor presenting with DDQ in the
presence of the acceptor alcohol furnished the intermediate acetal, whose anomeric
sulfide was then activated by iodonium di-
sym
-collidine perchlorate (IDCP) to effect
the intramolecular transfer. This protocol, which was characterized by the simulta-
neous introduction of two
-arabinofuranoside linkages, gave the pentasaccharide
b
target in 23% overall yield.
12.7.4. Synthesis of Sucrose
The synthesis of sucrose with its head to head linkage and its
a
-
D
-fructofuranosyl
unit, with its close relationship to
-
D
-arabinofuranosides, has been one of the
classical targets in carbohydrate chemistry [134]. In a major advance in the field,
Oscarson and Sehgelmeble made a fructosyl donor carrying a 1,4-
O-
(1,1,3,3-
tetraisopropyldisiloxane-1,3-diyl) acetal bridge (Scheme 12.50) locking C1 on the
a
b
-face [135]. This donor was shown to be an excellent glycosyl donor for the
formation of
-fructofuranosides, with a glucopyranosyl hemiacetal as acceptor.
The disaccharidewas obtained in 68%yield and gave sucrose after two deprotection
steps [135].
b
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