In glycopeptide synthesis

The high specificity and stereoselectivity of enzymes, as well as the mild conditions under which they react, make enzyme-catalyzed reactions versatile tools in the synthesis of glycoconjugates. In some instances, an enzymic one-step transformation affords higher yields then the conventional and more-complex chemical synthesis. The application of enzymes in glycopeptide synthesis is under active development for selective deprotection and glycosylation purposes. 

For glycopeptide synthesis, much attention has to be paid to the stereoselective formation of the natural-type glycosidic bond which must remain unchanged in the course of the synthesis. Therefore, in comparison to peptide synthesis, the compatibility and chemoselectivity of the applied reaction is fundamental in glycopeptide synthesis. 

Scheme 2 O- and /V-S ugar Protecting Groups Used in Glycopeptide Synthesis...

A major progress in glycopeptide synthesis was achieved when it was demonstrated that the NH2-terminal 9-fiuorenylmethoxycarbonyl (Fmoc) group can be selectively removed from glycopeptides using the weak base morpholine (pKa 8.3). This holds true for O-glycosyl serine and threonine esters, which are sensitive to base-catalyzed P-elimination of the carbohydrate [10]. 

Glycopeptides contain many functional groups of different reactivity as well as O- and /V-glycosidic bonds. Therefore, the compatibility and chemoselectivity of the applied reactions is a fundamental prerequisite in glycopeptide synthesis. In this chapter, efficient and generally applicable methods and their combinations will be illustrated by examples [5,8,91. 

Braun, P., Waldmann, H., and Kunz, H. (1992) Selective enzymatic removal of protecting functions heptyl esters as carboxy protecting groups in glycopeptide synthesis. Synlett 1, 39 10. 

Allyl, benzyl, phenylacyl and f-butyl esters are commonly used for protection of the carboxyl group. These esters can be removed without affecting the Fmoc group, and the resulting deprotected glycosylated amino acids can be used in glycopeptide synthesis. 

Mizuno Mamoru, Recent trends in glycopeptide synthesis. Trends in Glycoscience and Glycotechnology, 13, 69 11-30, 2001. 

Recent Developments in Glycopeptide Synthesis. Peters, S. Meldal, M, Bock, K. In Modem Methods in Carbohydrate Synthesis Khan, S. H., Oneill, R. A., Eds. Harwood Academic Chur T 1996, pp 352-377. 

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