Biomedical Engineering Reference
In-Depth Information
In addition, they further proved to be effective as efflux pump inhibitors and permeation
enhancers. The potential of thiolated chitosans to transfect plasmid DNA proposes a new
perspective for gene liberation to a targeted site. Along with thiolated chitosans as new
emerging biomaterials with promising properties, the combination of thiolated chitosans
with innovative technologies such as micro/nanotechnology is an optional choice as a
drug delivery system [191].
2.9 Sugar-Modified Chitosan
The first report on the modification of chitosan with sugars was by Hall and Yalpani (
cf.
Figure 2.19) in 1980 [192,193]. They synthesized sugar-bound chitosan by reductive
N-alkylation using NaCNBH
3
and unmodified sugar (1: method A) or a sugar-aldehyde
derivative (2: method B).
Sashiwa and Shigemasa [194] reported N-alkylation of chitosan performed in aqueous
methanol with various aldehydes, monosaccharides, and disaccharides (glycolaldehyde,
dl-glyceraldehyde, d-ribose, d-arabinose, d-xylose, 2-deoxy-d-ribose, d-glucose, 2-deoxy-
d-glucose,
3-
O
-Me-d-glucose,
d-galactose,
d-mannose,
l-fucose,
l-rhamnose,
and
GlcNAc).
Since the specific recognition of cells, viruses, and bacteria by sugars was discovered,
this type of modification has generally been used to introduce cell-specific sugars into
chitosan. Morimoto et al. [195, 196] and Morimoto and coworkers [197-198] reported the
synthesis of sugar-bound chitosans, such as those with d- and l-fucose, and their specific
OH
OH
Method (A)
OH
1)
O
O
O
HO
OH
OH
HO
OH
O
OH
O
OH
O
HO
O
HO
n
NH
2
2) NaCNBH
3
n
HO
NH
OH
OH
OH
O
O
HO
HO
2
OH
OH
OH
OH
2) NaCNBH
3
O
1)
O
CHO
HO
m
OH
m = 1 or 9
1
OH
O
O
Method (B)
HO
n
NH
OH
OH
O
O
3
HO
m
OH
Figure 2.19
Strategy for the substitution of sugars to chitosan by reductive N-alkylation.
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