Aldohexoses synthesis

Synthesis of aldohexoses from 422 (n = 2) telomers was achieved by way of cyanide intermediate s. On treatment with potassium cyanide, each of the dichloromethyl compounds 449 and 451 gave28 5 a pair of epimeric nitriles (463-466) that were converted, in moderate yield, into DL-galactose, DL-altrose, DL-idose, and DL-glucose by conventional procedures involving esterification, reduction, and final hydrolysis of the dichloromethyl group. 

The approach of Kunieda ami Takizawa is unique, in that elements of the carbon skeleton of the monosaccharide molecule form an acyclic frame up to the very final stage of the synthesis, and yet a high degree of selectivity is achieved, because of the all-tru ns geometry of the starting telomers. On the other hand, this situation limits the range of sugars synthesizable by this method. Only half of the aldohexoses,... 

K. Ranganayakulu, U. P. Singh, T. P. Murray, and R. K. Brown, Base catalyzed isomerization of epoxides to bicyclic allylic alcohols, potential intermediates for the total synthesis of the DL-aldohexoses, Can. J. Chem., 52 (1974) 988-992 and preceding papers. 

Application of the Kiliani-Fischer synthesis to the aldopentose D-arahinose produces aldohexoses D-glucose and D-mannose. Because the Kiliani-Fischer synthesis incorporates the stereocenters of D-arabinose without changes, D-glucose and D-mannose must have the same configurations at carbons 3,4, and 5 as does D-arabinose at carbons 2, 3, and 4, respectively. Furthermore, D-glucose and D-mannose must differ only in their configuration at carbon 2. 

A very useful synthesis of 5-amino-5,6-dideoxyaldohexoses entails the reaction of 5,6-di-0-(methylsulfonyl)aldohexoses with hydrazine and subsequent reduction. In this way, 3-0-benzyl-l,2-0-isopropyl-idene-5,6-di-0-(methylsulfonyl)-a-D-glucofuranose (67) gave the N-aminoaziridine compound (68). It must be assumed that the hydra-... 

The reasoning behind the Fischer proof is easier to follow if the eight possible D-aldohexoses are arranged in pairs of epimers at C2. These compounds are labeled 1-8 in Figure 27.9. When organized in this way, each pair of epimers would also be formed as the products of a Kiliani-Fischer synthesis beginning with a particular D-aldopentose (lettered A-D in Figure 27.9). 

A D-aldohexose A is formed from an aldopentose B by the Kiliani-Fischer synthesis. Reduction of A with NaBH4 forms an optically inactive alditol. Oxidation of B forms an optically active aldaric acid. What are the structures of A and B ... 

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... 

Crystalline L-altrose was described in 1934 by Austin and Humoller. After improving the methods for the preparation of L-ribose," they applied the cyanohydrin synthesis to 30 g. of that sugar and obtained 17 g. of crystalline calcium L-altronate and 14.5 g. of crystalline L-allono-7-lactone. Reduction of the latter with sodium amalgam yielded crystalline L-allose. The calcium L-altronate, by appropriate reactions, was converted to L-altrose, and the last of the sixteen theoretically possible aldohexoses had been prepared. Data on L-altrose and its derivatives are included in Table I. 

Anhydrofuranoses derived from all eight diastereoisomeric aldohexoses were described in the literature [6]. These compounds are formed as side products in the synthesis of 1,6-anhy-dropyranoses from free (or partially protected) sugars. Treatment of free sugars with toluene-p-sulfonic acid in DMF solution affords the furanose and pyranose 1,6-anhydrides with the furanose form up to 33% for the galacto-, alio-, and talo- isomers [3] the example is shown in O Scheme 9. 

The dissimilarity of the two ends of an aldohexose molecule prevents the existence of meso compounds (Sec. 4.18), and hence we expect that there should be 2 or 16 stereoisomers—eight pairs of enantiomers. All 16 of these possible stereoisomers are now known, through either synthesis in the laboratory or isolation from natural sources only three—(+)-glucose, (+)-mannose, (+)-galactose— are found in abundance. 

First, let us look at a method for converting an aldose into another aldose containing one more carbon atom, that is, at a method for lengthening the carbon chain. In 1886, Heinrich Kiliani (at the Technische Hochschule in Munich) showed that an aldose can be converted into two aldonic acids of the next higher carbon number by addition of HCN and hydrolysis of the resulting cyanohydrins. In 1890, Fischer reported that reduction of an aldonic acid (in the form of its lactone. Sec. 20.15) can be controlled to yield the corresponding aldose. In Fig. 34.2, the entire Kiliani-Ffscher synthesis is illustrated for the conversion of an aldopentose into two aldohexoses. 

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 ... 

Total synthesis of natural products containing x-substituted x-amino acid structures from aldohexoses using Overman rearrangement as the key reaction 04YGK693. 

Glucuronic acid pathway. The first part consists of synthesis of UDP-glucuronic acid and release of free D-glucuronic acid. The second part is the metabolism of D-glucuronic acid. D-Glucuronic acid is written as both the cyclic hemiacetal and the open-chain aldohexose and two orientations of L-gulonic acid and D-xylulose are shown. P = phosphate. 

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