Pentose derivatives, isomeric

Now the calculated values may be applied to additional, isomeric pentose derivatives. In the a-D-xylopyranose derivative the equilibrium is practically totally on the side of the 4Ci form (l ). Similarly, the p-D-arabinopyranose derivative totally adopts the 1C4 conformation (13). Consequently, neither... 

In work designed to develop syntheses of 3-deoxy-D-en/thro-pento-furanose compounds, Brown and Jones123 have studied additions to 3 - deoxy -1,2-0- isopropylidene - a - D - glycero - pent - 3- enodialdo -1,4-furanose (65, R = H), which was obtained by base-catalyzed elimination of p-toluenesulfonic acid from the corresponding 3-0-p-tolyl-sulfonyl-a-D-xyZo-pentose derivative. Partial, catalytic hydrogenation gave 3-deoxy-l,2-0-isopropylidene-/3-L-t/ireo-pentodialdo-l,4-fura-nose (66) which could, however, be isomerized, largely to the a-D-... 

Formyl-2-methylfuran was converted in 75% yield into derivative 319 by electrolytic methoxylation. A corresponding mixture of cis-diols (320) was treated with Dowex W-50 ion-exchange resin in methanol for four days, to afford 5-deoxy-3-C-(dimethoxymethyl)-DL-eryf/rro-4-pentulose dimethyl acetal (321). Reduction of this compound with lithium aluminum hydride or sodium borohydride gave a mixture of 5-deoxy-3-C-(dimethoxymethyl)pentoses, which was separated by column chromatography on silica gel, to give206 DL-streptose tetramethyl acetal (322) and the isomeric 5-deoxy-3-C-(dimethoxy-methyl)-DL-ribose dimethyl acetal 323 (hjxo ribo = 13 7). Detailed, combined gas-liquid chromatographic-mass spectrometric analysis of the compounds related to streptose (in the form of their trimethyl-silyl derivatives) has been described.207... 

In contrast to the formation of an osazone from phenylhydrazine and the 2-bromo-2-deoxy-hexoses derived from the adduct of tri-O-acetylglucal with bromine, two isomeric products [jwhich were assigned the D-threo-3,4-diacetoxytetrahydro-2-furaldehyde (p-nitrophenyl)hydrazone structures (21)] were isolated from the reaction between 3,4-di-0-acetyl-2-bromo-2-deoxy-D-tAreo-pentose (20) and (p-nitrophenyl)hydrazine. The... 

In the presence of sulfur compounds (e.g. cysteine) pentoses and methylpentoses produce, in addition to 4-hydroxy-5-methyl-2H-furan-3-one and 4-hydroxy-2,5-dimethyl-2ff-furan-3-one, respectively, related compounds containing sulfur in the molecule. Many of these compounds resemble the aroma of cooked or roasted meat. In the presence of primary amines, 1-deoxyhexo-2,3-diuloses derived from disaccharides yield pyridinium betaines and, further, pyrid-4-ones and isomeric 2-acetylpyrroles. The reaction with secondary amines leads to N-substituted... 

Crystal structure have been solved for most of the pentoses and hexoses, in one or more of the isomeric forms or as a 1-O-methyl derivatives. A significant amount of crystal structures of carbohydrates have been determined from neutron diffraction experiments. From these highly accurate structural determination, standard molecular dimensions of the constituting units have been established (Table 2). These data are an update of the ones published previously by Jeffrey Taylor [14] and, in a similar way, they can serve as a basis for parameterizations of molecular mechanics force fields. 

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