Conformational analysis aldoses

The chemistry of the 2,5-anhydrides of aldoses subsequently entered a prolonged lull, and Peat s review21 of 1946 in this Series does not report on any work later than 1925. The experimental basis of the deamination of amino sugars with nitrous acid was, nevertheless, established. The progress afterwards made in the conformational analysis of sugars made it possible for Shafizadeh22 to draw a parallel with the nitrous acid deamination of the aminocyclohexanols, and to rationalize the whole of these results. 

Fortunately, the rules of chemical reactivity and conformational analysis, coupled with the laws of thermodynamics, join forces to allow us to functionalize polyhydroxy aldehydes and ketones (aldoses and alduloses) in a selective and predictable fashion. 

Several reviews have already been published on the subject, for example, the acetala-tion of alditols [4], of aldoses and aldosides [5,6], and of ketoses [7]. Some aspects of the stereochemistry of cyclic acetals have been discussed in a review dealing with cyclic derivatives of carbohydrates [8], also in a general article [9] and, more recently, in a chapter of a monograph devoted to the stereochemistry and the conformational analysis of sugars [10], Aspects on predicting reactions patterns of alditol-aldehyde reactions are reviewed within a general series of books on carbohydrates [11]. The formation and migration of cyclic acetals of carbohydrates have also been reviewed [12,13],... 

Scheme 2. Mechanistic analysis of reaction pathways for NeuA catalysis that considers the crucial influences of C-3 and anomeric configurations and of chair conformations on the three-point attachment of aldoses as acceptor substrates, Si-face attack leads to regular (4S)-configurated adducts while re-face attack leads to inverted stereochemistry (abbreviations anm = anomerization, inv = ring inversion)...

The chiroptical properties of optically active thiazoUdines derived from aldoses and natural mercapto aminoacids was studied [92]. PMR parameters for thiazoHdine-4(R)-carboxylate derivatives were obtained by computer-assisted analysis of their spectra. The polyacetoxy-alkyl side chains have planar zig-zag conformations. The configurations at C-2 in the di-astereoisomers were ascertained on the basis of the Jnh.ch coupling constants [93]. The conformation and stereochemistry of diastereomeric sulfoxides of methyl 3-acetyl-5,5-dimethyl-2-(D-galactopentaacetoxypentyl)-1,3-thiazolidine-4-carboxylate 1-oxides were performed by H- and C-NMR spectral analysis [94]. 

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