Asparagine protection

The phenolic hydroxyl group of tyrosine, the imidazole moiety of histidine, and the amide groups of asparagine and glutamine are often not protected in peptide synthesis, since it is usually unnecessary. The protection of the hydroxyl group in serine and threonine (O-acetylation or O-benzylation) is not needed in the azide condensation procedure but may become important when other activation methods are used. 

Urge, L., Otvos Jr., L., Lang, E., Wroblewski, K., Laczko, I., and Hollosi, M. (1992) Fmoc-protected, glycosylated asparagines potentially useful as reagents in the solid-phase synthesis of N-glycopeptides. Carbohydr. Res. 235, 83-93. 

PG Pietta, P Cavallo, GR Marshall. 2,4-Dimethoxybenzyl as a protecting group for glutamine and asparagine in peptide synthesis. J Org Chem 36, 3966, 1971. 

Coupling of O-Acetate-Protected Mono- to Trisaccharyl Amines with Asparagine... 

If (he carboxylic acid concerned is a protected aspartic acid, an N-linked asparagine results, an observation that suggested that the procedure could be used for the preparation of glycopeptides. Accordingly, coupling of NPG 52 and aspartic acid 53 in acetonitrile solvent yields the N,N-diacyl derivative 54, which can be chemoselectively AT-deacetylated with piperidine in DMF to give asparagine 55 [19] (Scheme 13a). 

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