Biology Reference
In-Depth Information
(a)
OH
OH
OH
OH
O
cellulase
HO
O
HO
HO
F
O
O
O
HO
O
HO
O
OH
OH
OH
OH
n
cellulose
β
-cellobiosyl fluoride
(b)
OH
OH
O
OH
O
OH
O
α
-amylase
O
HO
O
OH
HO
HO
OH
O
O
OH
OH
HO
HO
F
n
α
-maltosyl fluoride
amylose
(c)
OH
OH
O
cellulase
HO
O
HO
HO
F
O
O
HO
O
O
HO
O
OH
OH
n
β
-xylobiosyl fluoride
xylan
Figure 2.4
Hydrolase-catalyzed polymerization of glycosyl fluorides to
synthetic cellulose (a), amylose (b), and xylan (c).
synthesis of chitin was first reported by utilizing chitinase
as a catalyst [26]. The chitinase-catalyzed enzymatic polymerization
of a
In vitro
'-diacetylchitobiose oxazoline monomer proceeded via
ring-opening polyaddition under weak alkaline conditions, giving a
synthetic chitin (Fig. 2.5a). The process of the higher ordered self-
assembly of the synthetic chitin during the enzymatic polymerization
was directly observed by phase-contrast and polarization
microscopes with SEM and TEM [27]. Hyaluronidase has shown a
wide spectrum of catalysis for the ring-opening polyaddition of a
variety of sugar oxazoline monomers, controlling stereochemistry
and regioselectivity perfectly to provide many natural and nonnatural
glycosaminoglycans [19]. For example, hyaluronan, which is a linear
polysaccharide having a repeating unit of
N,N
4)-
GlcA (GlcA, glucuronic acid) was produced by the hyaluronidase-
catalyzed polymerization of a GlcA-
β
-(1
3)-GlcNAc-
β
-(1
3)-GlcNAc oxazoline
monomer (Fig. 2.5b) [28]. Chondroitin, other glycosaminoglycan,
whose structure difference from hyaluronan is the difference in
stereochemistry of C-4 in hexosamine unit. Therefore, GlcA-
β
-(1
β
-(1
3)-
GalNAc oxazoline monomer (GalNAc,
-acetyl-d-galactosamine)
was designed for the synthesis of chondroitin via the hyaluronidase-
catalyzed ring-opening polyaddition (Fig. 2.5c) [29].
N
