Anomeric conformers

In tolnene-rfg, below 217 K, the benzyl aromatic signal resolved into two and the ben-zylic protons became diastereotopic. The exchange process, which was characterized by 217 = 246 s and AG = 10.2 kcalmoU, is a complex process involving both rotation aronnd the O—N bond and inversion at nitrogen, bnt since barriers to the former process are small the barrier best reflects that for rotation away from the anomeric conformation (Fignre 13). The amide isomerization barrier is even lower and both energies are in accordance with theoretical calcnlations (10.7 and 7.7 kcalmoG, respectively, for A—O rotation and amide isomerism in A-chloro-A-methoxyformamide) . 

Later studies from the same group (Asensio et al.94 ) have also shown that the a-Man-(l -> 3)-Man analogue (49) shows similar conformational behavior, with appreciable contributions of the non-exo-anomeric conformer. 

NMR nmol Complete structure, stereochemistry Detailed structural information (linkage, anomericity, conformation) Significant expertise required, low throughput, large amount of pure material required... 

Figure 11.22 Cooperativity among acceptors in the anomeric conformational equilibrium.

Since usually conformations that are recognized by proteins are preformed in aqueous solution we reinvestigated the solution conformation of sLe and Le to find out whether this non-exo-anomeric conformation is also present in aqueous solution. The presence of this minimum had been predicted recently on the basis of... 

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