Carbohydrates acylation

Study of the action of ammonia upon carbohydrate acyl esters originated some eighty years ago and, since then, many aspects of this complex reaction have been investigated. The processes that take place in this reaction include migrations, degradations, transesterifications, and deacylations, and their simultaneous occurrence makes the interpretation of the whole scheme very difficult. The present article provides a general description of the facts and a discussion of the different variables that play a role in the yields of products formed and in the mechanisms involved. 

REACTION OF AMMONIA WITH CARBOHYDRATE ACYL ESTERS 83... 

A limitation in the use of pivaloyl esters as protecting groups in a polyfunctional system is the harsh condition required for its cleavage (especially at sterically hindered secondary centers). The 4-acetoxy-2,2-dimethylbutanoyl (ADMB) esters have been proposed as an alternative because they are easily prepared, show similar reactivity in carbohydrate acylations, and are removed under much milder conditions (catalytic quantity of DBU at room temperature) [254]. 

Scheme 3.18 Regioselective protection of primary hydroxy groups of carbohydrates acylation...

Carbohydrate Acyl donor Main products Enzyme References... 

Figure 1. The structures of glycosylphosphatidylinositol (GPI) anchored protein in Trypanosoma sp. The conserved trimannosyl core, phosphoethanolamine linkage to protein and GlcN linkage to PI, are common to all GPI structures in eukaryotes. The specific modifications of this core in trypanosomes with carbohydrates, acyl groups, and ethanolamine or 2-aminoethylphosphonate are indicated.

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