Natural/unnatural sugar synthesis

Combined Use of Aldolases and Isomerases for the Synthesis of Natural and Unnatural Sugars... 

The allylation and crotylation of a-alkoxy aldehydes provide chiral 1,2-diol synthons which can be used in the synthesis of polyoj genated small molecules, for example, natural and unnatural sugars The tartrate-derived allylboronates I and 2 provide reagent-controlled selectivity in reaction with chiral glyceraldehyde acetonide 30. The intrinsic selectivity of the aldehyde is estimated by its reactions with pinacol allylboronates 33 and 34. The reagents 1 and 2 overcome the aldehyde s... 

Grouped in this Section are the C-D-pentofuranosyl-imidazoles, -pyrazolopyrimidines, and -adenines. The last two analogs are positional isomers of formycin in which the heterocyclic moiety is attached to the sugar at an unnatural position. A rationale103 for the synthesis of this type of analog is of interest it was based on the possibility of a close structural similarity between a natural adenine nucleoside and synthetic analog with respect to available hydrogenbonding sites. 

Jiang J, Biggins JB, Thorson JS (2000) A general enzymatic method for the synthesis of natural and unnatural UDP- and TDP-nucleotide sugars. J Am Chem Soc 122 6803-6804... 

Many natural and unnatural monosaccharides have been prepared by aldolase catalyzed condensation. The synthesized sugars were often dephosphorylated in situ by an acid phosphatase (Table 13-6, entry 3). These reactions illustrate multienzyme synthesis. In this case, no isolation of the phosphate intermediate is required both enzymatic reactions are run in the same pot after adjustment of the pH value. 

All previously described approaches to 3-deoxy-2-ulosonic acids started from advanced carbohydrate precursors, and thus they are not easily applicable to the synthesis of structurally diverse analogues. This concerns chemical syntheses relying on sugar-derived stereocenters and enzymatic ones, providing only very limited access to some naturally occurring compounds. In contrast, de novo syntheses starting from simple, achiral compounds offer much more flexible alternative approaches to synthesis of unnatural ulosonic acid analogues. 

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