Anomeric glycosylamines

When the amino group is at the anomeric position, the compound is normally named as a glycosylamine (see 2-Carb-33.6). 

TFA-labile TMS protection as shown in Scheme 39 may be advantageously employed as an alternative to the acetates.[123] This has also the advantage that the crude glycosylamines can be protected directly, as the TMS reagent does not react with the anomeric amine. 

Glycosylamines In these sugars, the anomeric -OH group (of common... 

The stereoelectronic situation of anomerically bound substrates is decisively influenced by the exo anomeric effect. Lemieux et al. [14] have found that the rotation around the exocyclic C-O-bond of glycosides is strongly hindered. This observation is interpreted as a delocalization of the lone pair of the oxygen into the a of the ring-C1 -O6 bond of the carbohydrate. Analogous n-a delocalization sterically adjusts glycosylamine derivatives in a preferred conformation (Scheme 2). 

The glycosylamine 296 anomerizes in methanolic solution. The spirohydantoins 298 and 299 form an equilibrium mixture under basic conditions [231] ( Scheme 60. 

Glycosylamines (NH2 on Cl) are configurationally unstable, but it is possible to measure the of the mixture and the difference between a- and (3-anomers by the technique described by eqn (2.8). The marginally stronger basicity of equatorial glycosylamines is attributed to the more ready solvation of their conjugate acids, but the anomeric effect makes the difference smaller than in carbocyclic systems. 

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