Lyxose solution

D-Lyxose diacetamide. Ammonia-silver oxide.y Ten grams of pentaaoetyl-n-galactononitrile was dissolved in 30 ml. of ethanol, and a solution of silver oxide (from 5 g. of silver nitrate) in 50 ml. of 30 % ammonia added. After two days at room temperature, the precipitated silver cyanide was removed by filtration and the solution evaporated in vacuo at 40° imtil all ammonia was eliminated. The residue was diluted with water and the soluble silver eliminated by treatment with hydrogen sulfide and filtration. The filtrate was treated with decolorizing carbon, filtered and evaporated to dryness. When the residue crystallized, it was suspended in warm ethanol and filtered yield, 2.5 g. (40%). After recrystallization from 60% ethanol, the product had a melting point of 230-231°. 

An analysis of Hn.m.r. data for aqueous solutions containing Ca " (and La ) ions and either o-lyxose or o-ribose has shown that predominantly 1 1 cation-sugar complexes are formed. The results also confirm the suggestion that metal complexation occurs with the pyranose in a conformation which has ax-eq-ax arrangement of the three consecutive cis-OH groups. 

N.m.r. studies of the binding of calcium and lanthanum ions to o-lyxose and D-ribose in aqueous solutions show the existence of 1 1 metal-sugar complexes. It has been suggested that the pyranose has a conformation which has ax-eq-ax arrangements of the three consecutive cis-hydroxy-groups. 

The aldehyde precursor, with the co-alkene derived from lyxose (42.0 mg, 0.12 mmol) was drawn into a syringe with a solution of 1 mL of THF-methanol (3 1 v/v) and added dropwise to a cooled solution ( 78°C) of Sml2 (3.6 mL, 0.1 M in THF), over 5 min. The solution was kept at —78°C for 1 h. When the reaction was complete, as indicated by TLC analysis, it was quenched with aqueous saturated sodium bicarbonate solution (1 mL) and extracted with ether. Chromatography using 50 50 ether-hexane gave 31.0 mg (73%) of pure syn-cyclic alcohol. 

Other than the absorption at 1718 cm", the freeze-dried material from equilibrated solutions of D-mannose, D-glucose, and L-rhamnose shows only the absorptions characteristic of the respective, crystalline a- and 8-pyranose forms. The lyophilizate of D-galactose solution showed similar behavior, except for an absorption band at 921 cm". The lyophilizates of equilibrated solutions of D-lyxose and D-talose show a number of absorption bands not found in the spectra for the crystalline anomeric pairs.  

D-Fucose (Rhodeose). Voto6ek obtained tetraacetyl-D-fucononitrile in 25% yield by treating D-fucose oxime with sodium acetate-acetic anhydride. The nitrile, degraded with ammonia and silver oxide, yielded 5-desoxy-D-lyxose diacetamide in 40% yield. The diacetamide compound was hydrolyzed with 5% hydrochloric acid and the 5-desoxy-D-lyxose was obtained in solution and characterized as the p-bromo-phenylosazone. Hydrolysis of the diacetamide compound with 6 N sulfuric acid was realized by Voto6ek and Valentin and the 5-desoxy-D-lyxose was isolated as a sirup. 

In summary, these peracylated derivatives lead to conformational equilibria, except in the case where the issue is particularly obvious a-D-xylo, Ci -D-arabino, C4 configurations). The free pentoses in aqueous solution still remain to be seen. The diaxial interactions are stronger than with the acetates and the anomeric effect is weaker. Out of the eight D-pentose configurations, four of them (jS-D-arabinose, a-D-lyxose, a-D-ribose, and jS-D-ribose) lead to a conformational equilibrium. 

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