Aldopentoses derivatives

CHAiUNCE The commercial synthesis of a useful heterocyclic derivative requires treatment of a mixture of aldopentoses (derived from corncobs, straw, etc.) with hot acid under dehydrating conditions. The product, E, has H NMR spectrum E, shows a strong IR band at 1670 cm, and is formed in nearly quantitative yield. Identify compound E and formulate a mechanism for its formation. 

Chain extension of the aldopentose ( —)-arabinose by way of the derived cyanohydrin gave a mixture of (-l-)-glucose and (-l-)-mannose. 

The synthetic procedure currently used consists in the direct oxidation of an isolated hydroxyl group in the sugar moiety of suitably protected nucleosides. In the meantime, the synthesis of some keto derivatives of aldopentose nucleosides by selective-elimination processes has been reported.4 8... 

Emil Fischer s initial studies [1] focused on dithioacetal formation from a variety of simple aldopentoses, aldohexoses, and aldoheptoses. The products were obtained by simply treating the sugar with an excess of ethanethiol in concentrated hydrochloric acid at low temperature ( 0°C). Many of these dithioacetals have low water solubility, crystallize spontaneously from the reaction mixtures, and can be isolated by simple filtration and washing with odd water. Fischer s key paper [1] also outlined most of the major reaction modes of the diethyl dithioacetal derivatives, later developed in detail, and thus paved the way for subsequent studies into this important class of sugar derivative. 

Thus, when the aldopentose diethyl dithioacetals are treated with 1 mole of p-toluenesulfonyl chloride in pyridine, cyclization to form a 2,5-anhy-dride is observed in each instance except in the arabino series, where a 5-O-p-tolylsulfonyl derivative can be isolated. It may be supposed (23) that the energy of activation for the cyclization reaction, being the difference between the ground-state and the transition-state energies, is smaller in those stereoisomers where conformational factors bring 0-2 into close... 

Aldopentoses (as l-phenyl-3- methyl-5-pyrazolone derivatives) Nucleosil silica, in-column 3-aminopropylated or Devosil NH2, 3 pm (25 mM HEPES-NaOH, pH 6.0)-acetonitrile (2 1) 345 mm x 100 pm i.d. 250 mm effective length 41 ... 

The Separation of Aldopentose and Aldohexose Diethyl Dithioacetal Derivatives by Gas-Liquid Partition Chromatography, D. T. Williams and J. K. N. Jones, Can. J. Chem., 44 (1966) 412-415. 

Two simple aldopentoses can be derived structurally from each of the four aldotetroses described, making a total of eight aldopentoses. Therefore, there are 16 aldohexoses. 

Figure 26 Comparison of the separate of PMP derivatives of aldopentose isomers on various columns (a) a column prepared by in-column 3-aminopropylation of Nucleosil silica gel (b) a column prepared by packing a commercial sample of amino silica, Develosil NH2, in an APTMS-treated capillary (c) a column prepared by packing Develosil-NH2 in an uncoated capillary. Eluent, (25 mM HEPES-NaOH, pH 6.0)-acetonitrile (2/1, v/v) sample concentration, 50 nmol in 100 pL of eluent injection, -2 kV for 3 s (from the cathodic end) applied voltage, -20 kV detection, UV absorption at 245 nm. Peaks Ara = D-arabinose, Xyl = D-xylose, Rib = D-ribose, Lyx = D-lyxose, all as PMP derivatives. (Reprinted from Ref. 111, with permission.)...

Like the 5-amino aldopentoses, the 5-amino aldohexoses have a pronounced tendency to form the pyranose ring in alkaline solution. In acid solution, three molecules of water are eliminated per molecule, to give the corresponding derivative of 3-pyridinol. 5-Amino-5-deoxyaldohexopyranoses are, however, distinctly more stable, as the Amadori rearrangement and pyridine formation occur at pH 5.7—6.2. With the pentose analogs, these reactions begin at pH 7—8. Because of the reactive a-amino alcohol arrangement at C-1, the 5-amino-5-... 

The following revised set of tables of the physical characteristics of the methyl ethers of the aldopentoses and rhamnose and fucose (and their derivatives) replaces those of R. A. Laidlaw and E. G. V. Percival, Advances in Carbohydrate Chem., 7, 1 (1952), and brings the subject up to date. 

It was in 1910 that Levene and Jacobs first applied the classical cyanohydrin synthesis to o-ribose (I), a five carbon atom aldehyde sugar (aldopentose) which had become more readily available through their earlier research on nucleic acids. Two new aldohexoses were thus obtained in sirupy form, and characterized by suitable crystalline derivatives. To one of these sugars was given the name allose, with configuration V, because it should be oxidizable readily to allomucic acid (VIII). The latter is an optically inactive, dibasic acid, described by... 

Fischer applied the Kiliani procedure (Scheme 1.1) to arabinose 5, an aldopentose obtained from sugar beet, and this produced the enantiomer 6 of the hexonic acid derivable from natural glucose (Figure 1.4). This observation led to the conclusion that the D-enantiomers of arabinose, glucose, mannose, and fructose all share the same configurations at their three highest numbered chiral centers. Moreover, the arabinose obtained from beet was the L-isomer. 

Horton, D, Koh, D, Stereocontrol in Diels-Alder cycloaddition to unsaturated sugars reactivities of acychc seven-carbon trans-dienophiles derived from aldopentoses, Carbohydr. Res., 250, 249-260, 1993. 

D. Horten and D. Koh, SteteocotUnd in Uds-AIder cydoaddidon to nnsntnrtted sugars Reactivities of acyclic 8eveit.catban irons dieaophiles derived fiom aldopentoses, Carbohydr. Kes. 250349 (1993). 

The four D aldopentoses and the eight D aldohexoses derived from them by Kiliani-Fischer synthesis are shown in Figure 25.9 (p. 1052), One of the eight aldohexoses is glucose, but which one ... 

The four o aldopentoses and the eight d aldohexoses derived from them by Kiliani-Fischer chain extension. 

The four D aldopentoses and the eight o aldohexoses derived from them by Kilianl-Flscher chain extension. 

Cyanohydrins derived from aldehydes are generally more stable than those from ketones (Ternay, 1976). Cyanohydrin formation is the first step in the well-known chain-lengthening sequence, the Kiliani-Fischer synthesis. For example, D-arabinose, an aldopentose, ultimately affords both o-glucose and D-mannose by this set of reactions (Carey, 2000b). 

---