Protecting groups in glycopeptide synthesis

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. 

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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. 

In solution, phase amino acid derived methyl ester N-Fmoc-Tyr-OMe 4 was successfully condensed under Mitsunobu conditions with 2,3,4,6-tetra-Oacetyl-D-glucose 2 to afford the fully protected glucosylamine 5. The reaction provides products of analytical purity and predictable stero-chemistry, as confirmed by H/ C NMR. Synthetic conditions and protective groups for glycopeptides synthesis have been investigated. Mitsunobu conditions employed in solution phase are based on the improved redox system l,l -azodicarbonyldipiperidine (ADDP)—tributylphosphine (TBP) in... 

Allyl (Al) esters are suitable for the temporary protection of carboxy groups in peptide and glycopeptide synthesisP " and also in the synthesis of cyclic peptides.In the latter case these esters allow, for example, on-resin head-to-taU cyclizations of peptides that are attached via the side chains of aspartic acid and glutannic acid residues to the solid support.t 1 The application of aUylic protecting groups in peptide synthesis has been comprehensively reviewed by Guibe.f ... 

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

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