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In-Depth Information
NO
2
HO
HO
OH
O
O
HO
O
O
HO
OH
O
HO
50
HO
R
OH
OH
48
:R=CH
2
OH
49
:R=CH
3
SH
S
SH
N
N
N
NH
N
N
HO
HO
HO
O
O
O
O
OCH
3
HO
HO
HO
OH
OH
OH
51
52
53
HO
HO
HO
Fig. 9 Substrates and inhibitors of galactofuranosidases according to de Ledekremer's
works.
SH
R
N
N
R
S
S
HO
HO
O
O
H
O
HO
HO
OH
O
O
H
HO
HO
54
Ara
f
51
Fig. 10 Remote activation of thioimidates catalyzed by thioligase from Araf51.
soils and involved in the degradation of biomass. In 2003, O'Donohue
and coworkers have synthesized several disaccharides with either
D
-Galf
or
L
-Araf entities bond to either furanoside or pyranoside,
111,113-115
even
to form non-natural disaccharides with fucofuranosyl or fluorinated
entities.
114
The regioselectivity of the coupling reactions were mainly
(1
3). It was further established that the eciency of the
biocatalyzed transfer was strongly dependent on the presence of the
2-hydroxyl on the donor.
116
Target di- and oligosaccharides were also
isolated with the assistance of Araf51 as furanosidase. Its important
versatility offered the opportunity to increase regioselectivity towards the
synthesis of (1
-
2) and (1
-
-
2), (1
-
3) and (1
-
5)-isomers. It was demonstrated that
the (1
-
2)-disaccharides were obtained under kinetic control, and that
the (1
5)-
regioisomer after a few minutes under similar conditions. Using the
Galf donor 48, the final isomers were the (1
-
2)- and (1
-
3)-disaccharides could isomerize into the (1
-
6)-difuranosides. It is
interesting to note that such compounds have high potential as
immunostimulating agents.
114,117-119
Further details are given in a very
recent review.
10
Mutation of the Araf51 also yielded a thioligase for the preparation of
thiofuranosides.
120
Within this study, thioimidate such as 54 was used as
a new donor in the biocatalyzed synthesis of carbohydrates and we have
also shown that the coupling reaction proceeded with remote activation
(Fig. 10).
-
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