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References 153

Furthermore, convergent reactions are useful for the in vitro synthesis of complex-
type glycoproteins and -peptides. Employing an endo-β-N-acetylglucosaminidase
(Endo-M) mutant glycosynthase from Mucor hiemalis, sialo-complex-type bioactive
peptides were produced by coupling sialo-complex-type sugar oxazolines and
GlcNAc carrying peptides or proteins. In this way, glycosylated RNaseB as a
model of sialo-complex-type glycoprotein could be synthesized [127]. Here two
independent cascade reactions were joined to a final product: On the one hand, the
chemo-enzymatic synthesis of sugar-oxazolines from natural sources and on the
other hand the chemical or enzymatic synthesis of the glycopeptide.

6.5
Conclusion

In this chapter, we have summarized striking examples of cascade reactions for the
chemo-enzymatic synthesis of glycoconjugates. The benefit of cascade reactions
without intermediate product work-up is emerging in the field of glycan synthesis.
Future studies should be therefore directed toward biocatalyst engineering and
process design to match the requirements for sequential, one-pot, and convergent
cascade reactions.

Acknowledgment

Financial support from EU ESF project COST CM 0701, from the DFG (SFB
985 and Research Training Group 1035 ‘‘BioInterface’’), and from the excellence
initiative of the German Federal and State Governments through ERS@RWTH
Aachen University is gratefully acknowledged. We thank Prof. Dr. Vladimir Kˇ ren
and his coworkers for the longstanding and fruitful collaboration.

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