Non-natural sugar

The synthetic value of this reaction has been enhanced by the development of a wide range of methodologies for glycal synthesis from 0-acylatcd glycosyl halides1 or from noncarbohydrate precursors. By use of the Lewis acid-catalyzed diene-aldehyde cyclocondensation reaction, glycals of natural and non-natural sugars can be obtained (Scheme 4).31... 

As a Chiral Starting Material in L Amino Sugar and l-Nucleoside Synthesis. The recent improved synthetic access to the (45)-aldehyde has facilitated non-natural sugar and nucleoside synthesis. Asymmetric synthesis of several L-amino sugars has been reported. Julia olefination of the (45)-aldehyde with the sulfone afforded the key olefin intermediate as a 4 1E/Z mixture, which was elaborated via Sharpless asymmetric dihydroxylation (SAD) and protecting group interchange to afford the protected 2-deoxy-2-amino-L-mannopyranose (eq 4). ... 

Non-Natural Sugar Analogues Chemical Probes for Metabolic Oligosaccharide Engineering... 

Measurement of Surface Display of Non-Natural Sugar Residues. 2144... 

Table 8. Transfer of non-natural sugars onto non-natural N-acyl glucosamide acceptors (compare Fig. 12)...

The first non-natural sugar derivative reported to be a substrate was 6-thio-D-glucose (45) which was found to be quantitatively converted into the corresponding D-fructopyranose 46 with sulfur in the ring (Scheme 18) [76]. In-depth investigations into the substrate tolerance of a D-xylose isomerase (Sweetzyme Q from Novo A/S, the enzyme from Streptomyces murinus sp.) were conducted by Bock and co-workers in 1983. 

When acetaldehyde is used as the only substrate, the initial aldol product can serve again as a suitable acceptor for sequential addition of a second donor molecule to give (3R,5R)-2,4,6-trideoxyhexose 133 (Figure 5.60) [282, 283]. Cyclization to stable hemiacetals masks the free aldehyde and thus effectively precludes formation of higher-order adducts. When the first acceptor is an a-substituted acetaldehyde, related aldol products from tv ofold donor additions can be prepared that are structurally related to mevino-lactone. Combination of a RibA-catalyzed initial addition to other aldolases such as FruA or NeuA in a consecutive addition reaction has also been studied for synthesis of non-natural sugars [277, 282]. 

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