Page 166 - Cascade_Biocatalysis_Integrating_Stereoselective_and_Environmentally_Friendly_Reactions

142 6 Chemo-Enzymatic Cascade Reactions for the Synthesis of Glycoconjugates

OH
O
HO
HO
R
OUDP
H O + 0.5O 2
2
a

HO OH O 2 c H O 2 HO O
2
O O
HO HO
R b R
OUDP OUDP
d HN S
O N
R = OH or NHAc H
O
H
N
N N
HO H O
O
HO
R
OUDP
HN S
O
N
H
e O H
N
HN N
HO H O
O
HO
R
OUDP

Figure 6.3 Cascade reaction for the chemo-enzymatic synthesis of biotinylated UDP-Gal
′
and UDP-GalNAc. (a) UDP-Glc(NAc)-4 -epimerase, (b) galactose oxidase, (c) catalase, (d)
(+)-biotinamidohexanoic acid hydrazide, and (e) NaBH CN [83, 84].
3
Another important immune-active glycan-backbone is LacdiNAc (GalNAcβ1,
4GlcNAc) and its analogs. A chemoenzymatic approach was used to access
LacdiNAc-mimetics using N-β-d-acetylhexosaminidase from Talaromyces
flavus [53]. A transglycosylation reaction with an enzymatically oxidized
GalNAcβ1-pNP-structure and GlcNAc was performed yielding the oxidized
LacdiNAc analog, which was further oxidized chemically with NaClO to access
4
GalNAcAβ1,4GlcNAc. A similar approach was used to synthesize the trisaccharides
GalNAcAβ1,4GlcNAcβ1,4ManNAc showing not only the usability of glycosidases
in preparative syntheses, but also the possibility of combining these enzymes with
subsequent chemical modification steps for the production of complex glycan
structures [52].