Arabinose aqueous solution

The reaction is used for the chain extension of aldoses in the synthesis of new or unusual sugars In this case the starting material l arabinose is an abundant natural product and possesses the correct configurations at its three chirality centers for elaboration to the relatively rare l enantiomers of glucose and mannose After cyanohydrin formation the cyano groups are converted to aldehyde functions by hydrogenation m aqueous solution Under these conditions —C=N is reduced to —CH=NH and hydrolyzes rapidly to —CH=0 Use of a poisoned palladium on barium sulfate catalyst prevents further reduction to the alditols... 

The procedure that Kuhn and Baschang99 had reported for the synthesis of NeuAc was extended by Hershberger and Binkley100 to a synthesis of KDO, as follows. Condensation of di-ter -butyl oxalacetate (85 see Scheme 25) with D-arabinose gave the epimeric mixture of lactone esters, 86 and 87, which was separated by fractional recrystallization. When 86 was heated in aqueous solution, the enol lactone, 88, was produced from 87, an enol lactone diastereomeric with 88 was obtained under these conditions. Compound 88 was converted into ammonium KDO by treatment with aqueous ammonia. 

A further quantity of arabinose may be isolated from the mother liquors by the use of diphenylhydrazine to a solution of 22 g. of diphenylhydrazine hydrochloride in 100 cc. of absolute methyl alcohol is added a solution of 3.3 g. of sodium in 50 cc. of methyl alcohol. After fifteen minutes standing the sodium chloride is removed by filtration and washed with methyl alcohol. The filtrate, which contains approximately 18 g. of free diphenylhydrazine, is added to the alcoholic mother liquor from the arabinose and the mixture is inoculated with diphenylhydrazone prepared from some of the crystalline arabinose. The mixture is allowed to stand overnight, and the crystalline diphenylhydrazone is filtered, washed with 95 per cent ethyl alcohol, and dried in a vacuum desiccator. In a preparation in which the yield of crystalline arabinose had been 23.5 g., the yield of diphenylhydrazone was 16.5 g., corresponding to 7.8 g. of the sugar. Arabinose can be recovered from the diphenylhydrazone by treatment with formaldehyde in aqueous solution. In view of the... 

This enzyme [EC 2.4.1.7], also known as sucrose gluco-syltransferase, catalyzes the reaction of sucrose with orthophosphate to produce D-fructose and a-D-glucose 1-phosphate. In the forward reaction, arsenate may replace phosphate as the substrate. However, the resulting product is unstable in aqueous solutions. In the reverse reaction, various ketoses and L-arabinose may replace D-fructose. See Arsenolysis... 

Dialysis experiments" have shown that Ca2 , Mg2 , Ba2 , and Sr2 form soluble chelates in aqueous alkaline solution with D-galactose, D-glucose, D-fructose, D-arabinose, D-ribose, maltose, and lactose. The absence of any precipitation of alkaline-earth metal hydroxide when an aqueous solution containing D-fructose and an alkaline-earth metal salt is made alkaline... 

Very few reports have been published on the use of X-rays for modification of starch, although the formation of deoxy compounds on irradiation of solid potato starch with 5 X 106 rads under nitrogen has been described. The amount of deoxy compounds formed is related almost linearly to the irradiation dose, and formation of 2-deoxy-D-arabi no-hexose is the major process there are almost no side-pro-cesses. Similar qualitative, but not quantitative, behavior is shown by 1% aqueous solutions of D-glucose, D-xylose, L-arabinose, D-ribose, sucrose, and cellulose powder (Fig. 14). Starch is the most resistant to irradiation among carbohydrates tested.74... 

D-glucal, an acetyl group is removed from diacetyl-L-rhamnal by boiling its aqueous solution. The resulting monoacetyl-L-pseudorhamnal, however, is not as stable as diacetyl-D-pseudoglucal.7 Oxidation of diacetyl-L-rhamnal with ozone yielded 5-desoxy-L-arabinose, which was characterized as its phenylosazone and p-bromophenylosazone. 7 Deacetylation of diacetyl-L-rhamnal yields crystalline L-rhamnal (XLIV).7... 

A corresponding equilibrium between the pyrrolidine form, the Schiff base, and the dimer exists in aqueous solutions of 4-amino-4,5-dideoxy-L-xylose. Its synthesis proceeds from D-arabinose to 5-O-p-tolylsulfonyl-D-arabinose diediyl dithioacetal, which is reduced to 5-deoxy-D-arabinose diethyl dithioacetal. This compound, in the form of its 2,3-0-isopropylidene acetal, is transformed into 5-deoxy-2,3-O-isopropylidene-D-arabinose diethyl acetal. p-Toluenesulfonyl-ation followed by treatment with sodium azide gives 4-azido-4,5-dideoxy-2,3-0-isopropylidene-L-xylose diethyl acetal, which is reduced in the presence of Raney nickel catalyst to 4-amino-4,5-dideoxy-2,3-0-isopropylidene-L-xylose diethyl acetal (104). 

With proper protection of certain hydroxyl groups, a desired degradation can take place. 3,4 5,6-Diisopropylidene-D-mannitol treated with sodium periodate in water at 0-5 °C for 30 min furnishes an 89% yield of 2,3 4,5-diisopropylidene-D-arabinose [1153]. Ethyl 2-acetamido-2-deoxy-1-thio-a-D-galactofuranoside yields 80% of a 4-formylthioacetalfuranoside on oxidation with an aqueous solution of metaperiodate at 0-3 °C (equation 300) [762],... 

There is one experimental report of such a process in liquids to date. Using two noncollinear frequency degenerate beams ((i), = m ) Shkurinov et al. report the observation of weak signals from aqueous solutions of arabinose that they attribute to the electric-dipolar pseudoscalar at fourth-order [4, 26]. 

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. 

Hydroxylation of the double bond is also an important result of the irradiation of o-glucal in aqueous solution in the presence of barium carbonate. n-Glucose and n-mannose are formed in considerable proportions, in the approximate ratio 1 0.8, when the irradiation is carried out in vacuo or in the presence of oxygen D-arabinose (formed by cleavage of... 

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