Alditols reactions

Branched-Chain Alditols. - Reaction of sugar oxiran derivatives with excess of trimethylaluminium yield branched-chain deoxy-alditol derivatives, e.g.. (8)—>(9), in an unusual ring opening, chain extension process. The conversion of the benzyl glycoside (10) to... 

The aldo or keto groups of carbohydrates can be readily reduced in aqueous solution at pH values between 6 and 10 with sodium borohydride to give sugar alcohols (alditols, reaction 4.35). The rate of the reduction can be accelerated by heating at 50°C. The reduction of ketoses results in two epimeric alditols (reaction 4.36). Use of tritiated sodium borohydride gives a tritium atom attached to C-1. 

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... 

Treatment of an aldose or ketose with NaBH4 reduces it to a polyalcohol called an alditol. The reduction occurs by reaction of the open-chain form present in the aldehyde/ketone hemiacetal equilibrium. Although only a small amount of the open-chain form is present at any given time, that small amount is reduced, more is produced by opening of the pyranose form, that additional amount is reduced, and so on, until the entire sample has undergone reaction. 

Efforts were made by Garcia Gonzalez and his coworkers to elucidate the mechanism of this reaction. In one of the working hypotheses, it was considered that the aldehydo form of the sugar and the 1,3-dicarbonyl compound undergo an aldol reaction to yield a 2-C-(alditol-l-yl)-l,3-dicar-bonyl compound, which is then dehydrated to form the furan. This hypothesis was supported by the isolation of the aldol-addition product of... 

The reaction of 1-amino-1-deoxyketoses, and their N-alkyl and N-aryl derivatives, with alkyl or aryl isothiocyanates (Huber et al, 1960) was studied in more detail, and new 4-(alditol-l-yl)-l-alkyl(aryl)-3-alkyl(aryl)-l,3-dihydro-2H-imidazole-2-thiones were obtained. These compounds were used as starting materials for the synthesis of OL-histidines, DL-histidine-2-thiol, and other imidazole derivatives of biological interest. 

Carboxyl redution. A sample of pennethylated PI (5 mg) was carboxyl-reduced by a modification of the method described by Lindberg and Lbnngren [9], as follows. The methylated fraction was solubilized and added a mixture of LiAlH4 (25 mg) in THF (5 mL) at 20 °C for 4 h. and refluxed during 1 h. The excess of reagent was destroyed with ethyl acetate (5-6 drops) and water (10 drops) and the pH of the mixture adjusted to neutrality with acetic acid. The insoluble residue was removed by centrifugation. The reduced fi action was precipitated with EtOH. The reaction was monitored by l.r. specroscopy. Hydrolysis products were analysed by GC-MS as methyl alditol acetates... 

The reaction of Pt(C03)(dppp)] with a modest excess of vicinal diols in CH2C12 solution affords the corresponding [Pt(a,/3-diolato)(dppp)] species under equilibrium conditions, a reaction that is readily reversed by the addition of dry ice to the product. The reaction with triols such as glycerol and alditol carbohydrates also affords the corresponding diolato species, with the reaction exhibiting excellent equilibrium regioselectivities for a number of isomers, of which the 7, 6-threo diols are the most favored. 

The alcoholysis of the cyclic phosphate of catechol by alditols can lead, after acid hydrolysis of intermediate, cyclic phosphates, to the selective formation of phosphoric esters of the primary hydroxyl groups in the alditols. Thus, erythritol and D-mannitol afford, after chromatographic purification of the reaction products, their 1-phosphates in yields of 31 and 38%, respectively.217 The method was used to convert riboflavine into riboflavine 5 -phosphate.218 1-Deoxy-1-fluoro-L-glycerol has been converted into the 3-(dibenzyl phosphate) in 54% yield by selective reaction with dibenzyl phosphorochloridate. 219... 

Reaction of dianhydro alditol 84 with lithium acetylides in the presence of BF3 Et20 followed by acidic work-up and catalytic hydrogenation affords 1,2-m-C-furanosyl compounds 86100 (Scheme 28). 

In addition to these physical studies at the Bureau, Tipson was able to return to his synthetic interests, both alone and in collaboration with other staff members. He was especially pleased to prepare D-talose in crystalline form, an accomplishment that had eluded Emil Fischer. Pursuing his longstanding interest in the reaction of sulfonic esters with iodide and following an earlier observation that the tetratosyl ester of erythritol is converted into butadiene by the action of sodium iodide and zinc, he demonstrated (with A. Cohen) that nonterminal unsaturation may be conveniently introduced into alditol derivatives by reaction of contiguous secondary sulfonates with sodium iodide and zinc dust in boiling A.A-dimethylformamide. This Tipson-Cohen reaction subsequently proved of great utility in other hands for the conversion of more complex carbohydrate structures into vicinal dideoxy derivatives. 

This enzyme [EC 1.1.1.21], also known as aldehyde reductase and polyol dehydrogenase (NADP ), catalyzes the reaction of an alditol with NAD(P) to generate an aldose and NAD(P)H. The enzyme exhibits a broad specificity for the alditol. 

This enzyme [EC 1.1.1.16] catalyzes the reaction of galac-titol with NAD to produce o-tagatose and NADH. The enzyme will also catalyze the conversion of other alditols containing an T-threo configuration adjacent to a primary alcohol group. 

The redox and complexation chemistry of alditol/Cr(VI) systems64 and the my<9-inositol/Cr(VI) system65 has been reported. In the first case, when an excess of the alditol over Cr(VI) is used, the secondary OH groups are inert to oxidation, and alditols are selectively oxidized at the primary OH group to yield the aldonic acid as the only oxidation product. The corresponding reaction involves a Cr(VI) —> Cr(V) —> Cr(III) reduction pathway, and the relative rate of each step depends on [H+] at... 

SCHEME 1. Schematic classification of the different oxo-Cr(V) species formed in the reaction between Cr(VI) and alditols (w denotes water). 

Galbis et al. described a variety of carbohydrate-based linear polyesters 61 of the poly(alkylene dicarboxylate) type that were obtained by polycondensation reactions of the alditols 2,3,4-tri-(9-methyl-L-arabinitol (9) and 2,3,4-tri-O-methyl-xylitol (10), and the aldaric acids 2,3,4-tri-(9-methyl-L-arabinaric acid (26) and 2,3,4-tri-(9-methyl-xylaric acid (27), butanediol, and adipic acid were also used as comonomers [28]. Copolyesters of the poly(aIkylene-c )-arylene dicarboxylate) type were obtained using bisphenols as comonomers (Scheme 1). Chemical polycondensation reactions were conducted in bulk or in solution. Enzymatic polycondensation reactions of adipic acid with the above-mentioned alditols were carried out successfully using Lipozyme and Novozyme 435. The hydrolytic degradations of some of these polyesters were also described. 

The separation of alditols as their trifluoroacetates has been reported by Shapira227 and by Japanese authors.213-228 The latter compared the reaction of trifluoroacetic anhydride in acetonitrile, tetra-hydrofuran, or ethyl acetate.213 They found that ethyl acetate is the most satisfactory, as acetonitrile causes tailing, and tetrahydrofiiran contains an impurity, not removed by distillation, which overlaps with fueitol per(trifluoroacetate). They found that, in ethyl acetate, mannitol reacts completely in 20 minutes, in contrast to the results of Shapira, who reported that hexitols require two hours at 35° when treated with trifluoroacetic anhydride and a trace of pyridine. The Japanese workers stated that the best separations were obtained on a column of 2% XF-1105, and that other columns, such as DC-1107, SE-30, or SE-52, caused tailing and broad peaks. 

A procedure has been reported473 for the direct determination, on a column of Polypak, of polyhydric compounds without conversion into derivatives. Separation of pentitols was not complete, but the method was found excellent for determining the amount of one alditol, as in the oxidation of L-arabinitol by Acetobacter suboxydans. This rapid method of monitoring the utilization of L-arabinitol permitted the reaction to be stopped as soon as all of the substrate had been consumed, before side reactions interfered. 

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