Aldopyranose

Scheme 1.—Occurrence of Ring Protons Expected to Have a Major Influence on the Relaxation Rates (R,) of the Anomeric Protons (H-1) of Aldopyranoses and Derivatives (4-25, Table I) in the C, or C4, Conformation.

Table 2 Percentage of cyclic and acyclic forms of D-aldopyranoses in water at 30 °C...

Since 2-deoxy-2-fluoro derivatives of aldopyranoses and furanoses are far more stable towards hydrolytic conditions than their 2-deoxy counterparts, the synthesis of the former entails primary preparation of the anomeric phosphotriesters 31, which are chromatographically separated into individual diastereomers and subsequently deprotected on phosphorus... 

The effect of alkoxyl or phosphate groups on the acidic degradation of sugars has not yet been systematically studied. The aldopyranoses substituted at 0-1, that is, the aldopyranosides, are only degraded... 

In studies on the anomerization of acetylated aldopyranoses in acetic anhydride-acetic acid-sulfuric acid at 25°, it was found34 that the peracetates of 6-deoxy-D-glucopyranose anomerize about ten times as fast as those of D-glucopyranose. 

The calculated, relative free-energies of the aldo-hexo- and -pento-py-ranoses are shown in Table I these values are relative to an imaginary aldopyranose in which there are no conformational interactions. From these values, the a / ratio can be calculated despite the simplicity and... 

Calculated Conformational Free Energies" and the Proportion of the a Anomer in Aqueous Equilibrium Solution of Aldopyranoses... 

MHz, H-N.m.r. Parameters for 5-Deoxy-5-C-phosphino- and -phosphinyl-aldopyranoses in CDC1 ... 

Investigations by Hough and coworkers134 have shown that 4-sulfonyloxy groups of aldopyranose derivatives can be displaced rather readily with thiocyanate and iodide ions this constitutes a potential route to 4-deoxy sugars. 

Fig. 6. Limited stereoselectivity in NeuA-catalyzed aldol additions, observed with aldopyranose substrates (including known anomeric ratios)...

If a sugar contains both an aldehyde and a ketone function, the aldehyde will form rings mainly the composition can be quite complex. Eight monomeric forms (out of a possible 18) were identified in the spectra of each of the pentos-2-uloses.36 The erythro isomer was found to consist, at 23° in D20, of 4.5% of the a-aldopyranose and 20.5% of its hydrate, 4.5% of the / -aldopyr-anose and 38.8% of its hydrate. 10.9% of the a-aldofuranose hydrate, 14.2% of the / -aldofuranose hydrate, 5.2% of the a-ketofuranose hydrate, and 1.1% of the / -ketofuranose hydrate. For the threo isomer, the composition, in the same order, wasfound to beO.9,59.8,1.0,29.1,1.5,1.3,1.0, and 5.4%. These compositions were also determined at 80°. 

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