Monosaccharides, furans from

Amino-2-deoxyaldohexoses, 1-amino-l-deoxyketohexoses, and their V-alkyl and JV-aryl derivatives react with /3-dicarbonyl compounds, giving substituted (tetrahydroxybutyl)pyrroles. It is, most probably, a general reaction of 2-amino-2-deoxyaldoses and 1-amino-l-deoxyketoses which parallels the formation of (polyhydroxyalkyl)furans from nonnitrogenous monosaccharides. In the reactions with amino sugars in alkaline media, simpler pyrrole compounds lacking the tetrahydroxybutyl chain are also obtained. 

In the period of 1972-1980 many syntheses of monosaccharides, starting from simple furan derivatives, have been completed. Only a few, however, consisted of a furan-into-furanoside transformation, in which the heterocyclic ring was maintained throughout. The majority of the syntheses described in this section made use of a furan derivative only as a substrate for construction of a principal intermediate unsaturated bicyclic, pyranoid, or acyclic compound, which was eventually converted into the desired monosaccharide or its simple derivative. 

Considerable effort has heen directed towards the synthesis of monosaccharide derivatives, and, in particular, C-glycosyl compounds, from Diels-Alder adducts offuran. Just and his group investigated the reaction of furan with a number of dienophiles, and described many interesting transformations of the adducts obtained from... 

The reversal of the well-known transformation of sugars into pyrans has been detailed as a method for assembling simple monosaccharides from simple furans (71T1973). A compound of the 2-furylcarbinol type was converted by the Br2/MeOH procedure into a mixture of the cis and trans isomers of the corresponding 2,5-dimethoxy-2,5-dihydrofuran derivative (129). Mild acid hydrolysis of (129) resulted in cleavage of the acetal bonds with formation of the dicarbonyl compound (130) which underwent immediate cyclization to 2,3-dideoxy-DL-alk-2-enopyranos-4-ulose (131 Scheme 29). 

The transformation of pentoses and hexoses into 2-furaldehyde and 5-(hydroxymethyl)-2-furaldehyde, respectively, by the action of acids is a well-known reaction. Professor Bognar was long interested in ascertaining whether this reaction is reversible. With both a theoretical and a practical goal, the Bogn r group then synthesized the dl forms of several important monosaccharides (xylose, ribose, and arabinose) from the aforementioned furan derivatives. 

Monosaccharide, aliphatic acids, furan derivatives, and phenolic compound recoveries after posthydrolysis were calculated as the ratio between the concentration determined in the reaction media and the concentration that resulted from the quantitative acid hydrolysis (29) of oligosaccharides into monosaccharides and other compounds. In enzymatic treatments, the concentrations obtained were corrected by subtracting the corresponding concentration in the respective control assays, since the commercial enzymes contain mono-, di-, and oligosaccharides. The dilution factor introduced by adding the dilute enzyme preparation or the different volumes of sulfuric acid in posthydrolysis were also accounted for. 

Gas chromatographic analysis allows the determination of the monosaccharides present by comparing the retention times with those of reference compounds. It is noteworthy to mention that the chromatographic profile is quite simple, because the deuterated compounds are not separated from the non-deuterated, even if a small difference in retention time can be evidenced by comparison of specific ion chromatograms. Each monosaccharide can give a maximum of four peaks, corresponding to the cd(3 and the pyran/furan isomers. 

De Novo Synthesis in Carbohydrate Chemistry From Furans to Monosaccharides and Oligosaccharides... 

The latter fraction was subjected to methanolysis and the product [33, Fig. (8)] analysed using one- and two-dimensional NMR techniques. The caryose proved to possess a uncommon new carbocyclic structure with a furane ring spirofused at C-4. The relative configuration of all carbinolic hydroxy groups was deduced from the evidence of several NOE-experiments. When the methylglycoside 33 was subjected to acid hydrolysis a mixture of three compounds was obtained. They proved to be the two anomeric furanose forms [34a and 34b, Fig. (8)] of the hydrolysed 33 and the pyranosidic isomer in its a-configuration [35, Fig. (8)]. On the basis of these results the structure 32 [Fig. (7)] is defined for this novel monosaccharide [105],... 

It might be presumed that by simple analogy, antibiotic monosaccharide 2-deoxy-L-fucose (14) could be best prepared from the corresponding hex-1-enitol (L-fucal), but scarce availability of the latter favors other routes. Total asymmetric synthesis from furan was elaborated by Vogel [50]. Alternative... 

A general method for the stereoselective synthesis of monosaccharides from furan compounds [30, 31] has provided a possible route to higher-carbon sugars. 

The relevant contribution of the output of annual plants to the realm of polymer synthesis and applications stems, instead, from some specific products, namely starch as a polymer, vegetable oils as triglyceride oligomers and hemicelluloses and monosaccharides as potential monomers or precursors to furan derivatives. 

Anomers also appear in cyclic form as five-membered rings, for instance in the monosaccharides fructose and ribose. These cyclic molecules are named furanoses because of their similarities to the cyclic ether furan. Starting from D-fructose and D-ribose, the cyclization yields anomers a- and p-D-fructofuranose, as well as a-and P-D-ribofuranose, respectively. 

Dimethoxy-2,5-dihydrofurfuryl alocohl dissolved in 2%-H2S04, and allowed to stand 1.5 hrs. at room temp. 2,3-dideoxy-DL-pent-2-enopyranos-4-ulose. Y ca. 100%. - This is a stage of a multi-step conversion of furan derivs. into monosaccharides. F. e. s. O. Achmatowicz, Jr., et al.. Tetrahedron 27, 1973 (1971) 6-hydroxy-2,6-dihydro-3-pyrones from furylcarbinols by oxidative ring expansion cf. Y. Lefebvre, Tetrah. Let. 1972, 133. 

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