Page 169 - Cascade_Biocatalysis_Integrating_Stereoselective_and_Environmentally_Friendly_Reactions

6.2 Sequential Syntheses 145

HO
HOOC HO O OH
O
HO
HO O
OH
1. KfiA, UDP-GlcNTFA
2. pmHS2, UDP-GlcUA

OH
HOOC
O O
HO O HO
HO HO
OH OH
TFAN HOOC HO O = R
O
O
HO O
OH
1. KfiA, UDP-GlcNTFA
2. pmHS2, UDP-GlcUA
3. KfiA, UDP-GlcNAc
OH
O
HO OH
HO HOOC
ACHN O O
O O
HO HO
OH
TFAN
O R
O
1. TEA, MeOH, H 2
2. NST, PAPS
3. C 5 -epimerase, 2-OST, PAPS
4. 6-OST, PAPS
5. 3-OST-1, PAPS

ULMW heparin

Figure 6.5 Sequential synthesis for the production of ultra low molecular weight (ULMW)
heparin. Each multi-arrow represents a cascade reaction. In total, three sequential cascades
with 2–5 steps are combined to yield the product [91].
chemical coupling. UDP-GlcNAc and UDP-GlcA were used to control subsequent
individual glycosylation steps.
Recently the on-chip glycosylation with nanoscale droplets of β1,4GalT, α2,3SialT,
and α1,3FucT on an immobilized substrate was reported [95]. The synthesis was
carried out either in a spot-wise manner or in a full-well format, building-up an
N-glycan array. The enzymes were applied in a sequential mode with intermediate
washing steps. Immobilizing substrates and using nano-droplets for glycosylation
may become important for future cascade reactions on arrays.