Talose 2,5-anhydro

Methanol fiihrt weder zu dem erwarteten 2-Fluor-2-desoxy-Derivat, noch zu dem moglichen 2-0-Methylather. Unter Ringumlagerung entstehen hierbei die beiden Methylglykoside der 2,6-Anhydro-3,4-0-isopropyliden-D-talose 110,139) ... 

Die Desaminierung von Aminozuckern fiihrt in manchen Fallen zu ver-schiedenen Anhydro-Derivaten. Im Falle der 4-Amino-4-desoxy-l,6-anhydro-fl-D-mannopyranose wurde unter Waldenscher Umkehr am C-4 die l,6-3,4-Dianhydro-j3-D-talose erhalten is.nv). 

The key sequence in the determination of the structures of 2,5-anhydro-D-mannose (2) and -D-talose (4) was their reduction to the corresponding 2,5-anhydroalditols (5 and 6) and identification of the asymmetric dialdehyde (7) resulting from oxidation of the anhydro-alditols with periodate.37,43... 

Quite analogous ring-closures occur when the 1-O-acetyl derivatives of the rhamnopyranose and talopyranose derivatives are treated with sodium azide in N,N-dimethylformamide. l-O-Acetyl-6-deoxy-2,3-0-isopropylidene-4-0-mesyl-a-L-mannopyranose is converted exclusively into l,4-anhydro-6-deoxy-2,3-0-isopropylidene-/3-L-talo-pyranose. In this instance, the azide nucleophile attacks the l-O-ace-tyl group, liberating an 0-1 oxide ion which reacts with inversion of C-4. The 4-epimeric, l-O-acetyl-6-deoxy-talose derivative gives 60% of the direct inversion product l,4-anhydro-6-deoxy-2,3-0-isopropyli-dene-a-L-mannopyranose, together with other products.50... 

Formation of neither a furanose nor a pyranose form can occur for 2,5-anhydro-D-talose, and the mutarotation reported for an aqueous solution must be due to hydration of the aldehyde group, or other processes,6,75 or both (see p. 20). 

Numerous epoxy sugars have been hydrolyzed in aqueous base, among them almost all the possible 2,3-anhydro-4,6-C>-bentylimethyl glycosides of n-talose,887- 11 u-gulose,697-1611 n-mannose,874 and D-aUose8 - iiM,i4M,i 7t indicated in Eq. (542). 

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 2-0-(2-amino-2-deoxy-D-galactosyl)glycerol (34, R = H) was smoothly degraded by nitrous aoid to glycerol and 2,5-anhydro-D-talose (3S), and the W-acetyl derivative (35, R = Ac) reduced 1 molar proportion of periodate, giving neither formaldehyde nor formic acid during (84) P. J. Stoffyn and R. W. Jeanlos, Arch. Biochem. Biophyi., 52, 373 (1054). 

T. Ogawa, M. Matsui, H. Ohrui, H. Kuzuhara, and S. Emoto, Synthetic studies on C-nucleosides. 6. Synthesis of 2,5-anhydro-3,4,6-tri-0-benzyl-L-talose dimethyl acetal via... 

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. 

Reeves has suggested that the spontaneous formation of 1,6-anhydro derivatives of idopyianose and altropyranose may be due to the conformational behavior of the aldoses his instability factors show that /3-Didose and /3-D-altrose will exist partly in the conformations favorable for closure of the 1,6-anhydro ring. This reasoning could lead to the further conclusions that D-talose, but probably not n-gulose, should fairly readily afford a 1,6-arihydro derivative of the pyranose form. 

J. Defaye, Desamination nitreuse de la D-galactosamine. Preparation des 2,5-anhydro-D-talose et 2,5-anhydro-D-talitol, Bull. Soc. Chim. Fr. p. 999 (1964). 

Moving clockwise around the pyranose ring, the next example is provided by the deamination of 4-amino-1,6-anhydro-4-deoxy-/3-n-mannose (LXXII), which gives 1,6 3,4-dianhydro- 3-D-talose (LXXIII). There is some evidence indicating that the parent compound 1,6-anhydro-/3-D-mannopyranose, which cannot adopt the usual chair conformation (Cl), favors the reverse chair conformation (1C) to the alternative boat form (SB) Thus, we can assume that the above derivative also favors the reverse chair conformation LXXII and that the anhydro sugar is formed through the mechanism involving axial and antiparallel substituents. 

D. Horton and J. S. Jewell, Synthesis of l,6-anhydro- 3-D-talopyranose from derivatives of D-galactose and D-mannose, Carbohydr. Res., 5 (1967) 149-160 G. J. F. Chittenden, Oxidation of some derivatives of D-galactose with methyl sulphoxide-acid anhydride mixtures a route to derivatives of D-glucose and D-talose, ibid., 15 (1970) 101-109. 

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