Hexopyranosides methyl 2,3-anhydro

C13H2206 3,2 -Anhydro-[methyl 2,6-dideoxy-4-0-(3,6-dideoxy-a-D-riho-hexopyranosyl)-a-D-Zt/xo-hexopyranoside] (MADRFU)256... 

On their side, Yin and Linker [216] made use of a 2-C-branched hexopyranoside, the synthesis of which was achieved by addition of dimethyl malonate to tri-O-benzyl-D-glucal (TUPAC name 3,4,6-tri-0-benzyl-l,5-anhydro-2-deoxy-D-araZtino-hex-l-enitol, Scheme 45) [217], Thus, saponification of the 2-C-[bis(meth-oxycarbonyl)]methyl derivative 184 to the corresponding malonic acid 185 was followed by heating in refluxing toluene. This led to decarboxylation and lactoniza-tion giving 186. The method was optimized and applied to the synthesis of pentoses and disaccharides. 

The first of these methods involves the reaction of triphenyl phosphite methiodide with methyl 3-0-methyl-2-0-p-tolylsulfonyl-a-D-glucopyrano-side, hydrogenation of the resulting 4,6-diiodo derivative, and hydrolysis,186 as adapted to monosaccharides by Kochetkov and coworkers.1,0 In another approach,281 ethyl 2,3-anhydro-4,6-dideoxy-D-nbo-hexopyranoside, obtained from desosamine, was treated with sodium methoxide, to give a mixture of 2- and 3-methyl ethers. After fractionation and separation of side products,288 the 3-methyl ether was hydrolyzed, to give crystalline chalcose. McNally and Overend800 have described another synthesis, starting from methyl 4-deoxy-D-xj/Zo-hexoside.107... 

All stereocenters in 1,6-anhydrohexopyranoses are of inverted orientation compared to those in the parent 4Ci(d) or 1C4(l) conformations of the corresponding hexopyranoses for example, see 21, 23, and l,6-anhydro-/J-D-glucopyranose (22). In chemical properties, these compounds resemble to a certain degree the methyl /f-D-hexopyranosides. They are relatively stable in alkaline media, but are readily hydrolyzed by acids. In aqueous acid solution, an equilibrium is established between the 1,6-anhydrohexo-pyranose and the corresponding aldohexose, whose composition correlates with expectations from conformational analysis and calculations from thermodynamic data.121 Extreme values, 0.2 and 86%, are observed respectively with 1,6-anhydro-/f-D-glucopyranose (22) and l,6-anhydro-/f-D-idopyranose (the latter has all hydroxyl groups in equatorial disposition). 

All cofigurational isomers of 2,3- and 3,4-anhydrohexopyranoses have been described. Generally, they adopt more or less flexible half-chair conformations (H) dependent on the absence or presence of an additional fused ring. Examples of the latter compounds are methyl 2,3-anhydro-4,6-O-benzylidene-a- and /1-hexopyranosides of the alio 70,272,273 manno 71,273 275 gui0 216,211 an(j 276 c0nfigurati0nS. 

J. Yoshimura, N. Kawauchi, T. Yasumori, K. Sato, and H. Hashimoto, Branched-chain sugars. 37. Synthesis of 2,3-anhydro-hexopyranosides and 3,4-anhydro-hexopyranosides having a methyl branch on the oxirane ring, and their reactions with some lithium methylcuprate reagents, Carbohydr. Res., 133 (1984) 255-274. 

P. Koll and F. S. Tayman, 2,5-Dioxabicyclo[2.2.2]octan-Derivate Methyl-2,6-anhydro-D-hexopyranoside mit talo- und aftro-Konfiguration, Chem. Ber., 112 (1979) 2296-2304. 

At pH 10, diphenylborinic acid gives a tetrahedral anion that complexes with various diol systems, and thus it can be used in electrophoresis like borate.109 In a more detailed study of such complexing,110 diols were examined by 13C-n.m.r. spectroscopy, before and after addition of sodium diphenylborinate, and complexes were detected, and their spectra observed, for a variety of carbohydrate derivatives. 1,2-Diol groupings in acyclic and cis-cyclic compounds, 1,3-related diols at C-4,C-6 of hexopyranosides, the 3,5-diols of glucofuranoses, and 2,4-diols of the anomeric methyl 3,6-anhydro-D-glucopyranosides were all found to react. No interaction occurred with l,6-anhydro-/3-D-glucopyranose (compare Section V,2). 

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