6- deoxy-L-talose

Conversion of L-fucosyl- and 3 -0-methyl-D-glycosyl-purines into nucleosides of two naturally occurring, rare sugars, 6-deoxy-L-talose and 3-O-methyl-D-mannose, could be achieved57 by stereospecific reduction at C-2 of 7-(6-deoxy-3,4-0-isopropylidene-/ -L-h/xo-hexopyranosyl-2-ulose)theophylline (35a) and 7-(4,6-0-benzylidene-3-0-methyl-/ -D-orobtno-hexopyranosyI-2-ulose)theophylline (8). Treatment of 35a and 8 with sodium borohydride in ethanol afforded the expected 7-(6-deoxy-3,4-0-isopropylidene-/ -L-talopyranosyI)theophylline (84) and 7-(4,6-... 

Jones and Nicholson234 have observed that treatment of 2-O-sulfonyl sugars with base leads to epimerization at C-2. In this way, 2-O-p-tolyl-sulfonyl-L-fucose (42) was converted into 6-deoxy-L-talose (44) in high yield. A possible intermediate might be the 1,2-anhydro sugar (43). 

The instability of TDP-6-deoxy-L-talose should be mentioned. When using the routine procedure for the isolation of TDP-rhamnose, a consistent loss of the 6-deoxy-L-talose nucleotide was observed. A systematic study revealed that in contrast to the rhamnose derivative, the 6-deoxy-L-talose nucleotide was extremely labile to alkali. Prolonged exposure to pH 8.0 at 37 °C resulted in significant degradation. The degradation products are TMP and 6-deoxy-L-talose monophosphate. Careful degradation studies provided experimental evidence for its identification as cyclic-l,2-monophospho-6-deoxy-L-talose. The extreme alkali lability... 

Forsberg, L.S., Bhat, U.R., Carlson, R.W. Structural characterization of the O-antigenic polysaccharide of the lipopolysaccharide from Rhizobium etli strain CE3. A unique O-acetylated gly-can of discrete size, containing 3-0-methyl-6-deoxy-L-talose and 2,3,4-tri-O-methyl-L-fucose. J Biol Chem 275 (2000) 18851-18863. 

Nakano, Y., Suzuki, N., Yoshida, Y., Nezu, T., Yamashita, Y., Koga, T. Thymidine diphosphate-6-deoxy-l-lyxo-4-hexulose reductase synthesizing dTDP-6-deoxy-l-talose from Actinobacillus actinomycetemcomitans. J Biol Chem 275 (2000) 6806-6812. 

By analogy to results obtained in studies on the biosynthesis of dTDP-L-rhamnose,18 dTDP-6-deoxy-L-talose,17 and GDP-L-fucose,41 it seems very likely that dTDP-6-deoxy-L-/yxo-hexos-4-ulose (21), formed by the 3,5-epimerase reaction, remains enzyme-bound. 

Desulfonylation of 2-O-p-tolylsulfonyl or 2-0-(methylsulfonyl) derivatives of D-arabinose, D-xylose, and L-fucose with aqueous barium hydroxide yields D-ribose, D-lyxose, and 6-deoxy-L-talose, respectively, by way of a 1,2-anhydro sugar similarly, 3-0-(methyl-sulfonyl)-D-fructose affords D-psicose. 

SCHEME 13. 33 Mukaiyama s asymmetric aldol reactions total synthesis of D-ribose, 4-C-methyl-D-ribose and 6-deoxy-L-talose. 

Deoxy-L-talose (20) sarmentoside A and related substances acolongifloroside K 80 174, 176 181 Strophanthus thoUonii Strophanthus sarmentosiis Acokanthera longifiora and others Actinomyces bovis Mycobact. avium Pseudomonas pseudomallei cell walls after hydrolysis Mycoside C antigen K after hydrolysis 182, 183 182, 184,185 182... 

Occurrence. 6-Deoxy-L-talose (38) was first isolated from the cardiac glycoside sarmentoside A.177 Other cardiac glycosides isolated from several plants contain 6-deoxy-L-talose.160... 

The exopolysaccharide of Burkholderia caribensis strain MWAP 71 contains 6-deoxy-L-talose.178 Other strains of Burkholderia pseudomallei incorporate 6-deoxytalose, as a polymer with D-glucose but its configuration has not been established.174... 

Deoxy-L-talose is also present in the glycan moiety of lipopolysaccharides (LPS) of several bacteria. For example, 38 was recently characterized in the trisaccharide repeating unit of the lipopolysaccharides isolated from Rhizobium legumi-nosarum, in which it was attached as a side chain, a-(l->2)-linked to rhamnosyl residues.179... 

---