Glucopyranose, 1,2-anhydro anomerization

Support for this result was obtained from the taste of 1,5-anhydrohexitols, which, only for purposes of comparison, can be regarded as 1-deoxyal-dopyranoses. 1,5-Anhydro-D-glucitol (that is, the incorrectly named 1-deoxy-D-glucopyranose ) (14), 1,5-anhydro-D-mannitol ( 1-deoxy-D-mannopyranose or 2-deoxy-D-fructopyranose ) (15), and 1,5-anhydro-D-galactitol ( l-deoxy-o-galactopyranose ) (16) are all purely sweet, without any trace of bitterness. Furthermore, the complete absence of bitterness of 1,5-anhydromannitol (16) clearly indicates that the anomeric... 

A few other examples may be found in related series. For instance, the methylenoxy bridge of l,6-anhydro-/3-D-glucopyranose can be cleaved, with subsequent bromination at both C-6 and the anomeric center.163... 

Evidence of complexing was obtained with the anomeric methyl 3,6-anhydro-D-glucopyranosides (see Table II), which suggests that the oxygen atoms on the pyranoid ring can play a role in ester stabilization (45) but, with l,6-anhydro-/3-D-glucopyranose (46), no complex was... 

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). 

Most of the acetylated monosaccharides afford the more stable anomeric fluoride in this process. However, the action of a solution of hydrogen fluoride in acetic anhydride on 1,6-anhydro-j8-D-glucopyranose triacetate (1) gave tetra-O-acetyl-jS-D-glucopyranosyl fluoride (3). This result is prob-... 

In the second approach to 1,6-anhydro sugars, anomeric esters, particularly glycosyl acetates, are activated by Lewis acids and displaced by labile ethers at 0-6. Rao has reported an efficient synthesis of tri-0-acetyl-l,6-anhydro-/3-D-glucopyranose by treatment of the trityl ether (4) with titanium chloride (O Scheme 3) [20]. 

To overcome the problems derived from formation of anomeric mixtures when O-benzylated glycosyl halides are used as precursors, Ledford and Carreira52 have disclosed an elegant synthesis of 2,3,4-tri-O-benzyl-a-D-glucopyranosyl isothiocyanate (10) based on the use of l,6-anhydro-2,3,4-tri-0-benzyl-/t-i)-glucopyranose (9) as the glycosyl donor. Treatment of 9 with tetra-n-butylammonium thiocyanate and boron trifluoride-etherate complex provided 10 in 50% yield with total control of the anomeric configuration (Scheme 5). 

The anomeric configurations in a-D-fructofuranose g-D-fructo-furanose 2, 1 2,3 -dlanhydrlde, a product formed in high yield by the action of a D-fructotransferase on Inulln, have been determined from its C-n.m.r. spectrum.A H-n.m.r. study on tosylated derivatives of 1,6-anhydro-g-D-glucopyranose is mentioned in Chapter 20. 

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