2,3-Unsaturated pentose

An unsaturated pentose derivative (25a), as an intermediate, was also proposed for the enzymie formation of 2 -deoxyeytidine 5 -phosphate from cytidine 2, 5 -diphosphate (25). 

Acetamido-3,4-di-61-acetyl-6-deoxy-D-glucal on reaction with ammonium nitrate-trifluoroacetic anhydride in aqueous sodium bicarbonate affords the unsaturated pentose compound 31 whereas reaction with mercury(II) sulfate and sulfuric acid gave the expected -alkene 32. ... 

Very little work on the synthesis of pentitols had been carried out before 1928. Those pentitols which had been synthesized were made by the reduction of pentoses. Several pentitol intermediates had been synthesized" and it seemed desirable to attempt to complete the synthesis of pentitols from the unsaturated intermediates, using the methods which had been successfully employed in the synthesis of hexitols. 

In the pentose series, attack has also been observed to occur mainly from the less-hindered side of the double bond, as in the addition of trifluoro(fluoroxy)methane to di-O-acetyl-D-arabinal. Trifluoromethyl 3,4-di-0-acetyl-2-deoxy-2-fluoro-/3-D-arabinopyranoside and 3,4-di-0-acetyl-2-deoxy-2-fluoro-/J-D-arabinopyranosyl fluoride were obtained,72,74 together with a very small proportion of 3,4-di-0-acetyl-2-deoxy-2-fluoro-a-D-ribopyranosyl fluoride.74 With di-O-acetyl-D-xylal, however, the lyxose derivatives were mainly obtained.72,73 The suggestion has been made73 that the greater conformational mobility of pentopyranoses results in a preponderance of the C d) conformer of the D-lyxose derivatives,72,73 such that F-l and CFsO-l are axially disposed. For further reactions of unsaturated carbohydrates with tri-fluoro(fluoroxy)methane, see Section 11,9. 

Carbohydrates Ceiiuiose Starch 1 Hemiceiiuiose Lignin J ( monosaccharides "j ( hexoses "j Cx(H20)y < oligosaccharides > pentoses > [ chitin J ( glucosamine J (C2H20)4 unsaturated aromatic alcohols —> polyhydroxy carboxylic aoids HPOy, GO2, CH4, glucose, fructose, galactose, arabinose, ribose, xylose... 

Several new routes to 2,3-, 3,4-, and 5,6-unsaturated sugars (which are, in essence, potential syntheses for the respective dideoxy sugars) have now been developed. 14 A 2,5-dideoxy-D-erj/reductive desulfonyloxylation of 2-deoxy-... 

Furoic acid (furan-2-carboxylic acid, or pyromucic acid) is used as a bactericide, and the furoate esters are used as flavoring agents, as antibiotic and corticosteroid intermediates. It is obtained by the enzymatic or chemical/catalytic aerobial oxidation of furfural (2-furalaldehyde) the latter is the only unsaturated large-volume organic chemical prepared from carbohydrates today. D-Xylose and L-ara-binose, the pentoses contained in the xylan-rich portion of hemicelluloses from agricultural and forestry wastes, under the conditions used for hydrolysis undergo dehydration to furfural. 

Otherwise, unsaturation may be introduced by use of carbonyl-containing carbohydrate derivatives and carbon nucleophiles that contain alkene (or, if desired, alkyne) functionality, a notable illustration being the tin-or indium-mediated C-l allylation of unprotected sugars. As an illustration, D-arabinose, treated with allyl bromide in aqueous ethanol in the presence of tin gives, after acetylation, 278 in 85% yield.258 In this procedure aldoses react better than do ketoses, and pentoses better than hexoses. More usual is the use of Grignard reactions to give, for example, the octynes 279. 

Wittig reactions of a-alkoxy aldehydes and sugar lactols, such as pentose ketal (48), with stabilised ylides usually proceed with low ( )-selectivity. However, Harcken and Martin have discovered that treatment of these aldehydes with (methoxycarbonylmethylene)tributyl phosphorane (49) and a catalytic quantity of benzoic acid produces the heptenonate (50) with a E Z ratio of 95 5. The stereoselectivity of the reactions between aldehydes and spirophosphoranes (51) has been examined and the phosphoranes found to favour the formation of (Z)-a,p-unsaturated aldehydes and amides. ... 

Hexose 5,6-unsaturated sugars or pentose 4,5-unsaturated sugars are the only examples discussed in this section where the unsaturation is endocyclic to the ring itself. Interestingly, this type of unsaturated sugar is also an enol ether, and can react as enol ethers generally do [78]. 

Previous sections presented approaches towards replacing the primary hydroxyl group at C-6 (hexoses) or C-5 (pentoses) with halides. These modified sugars are easily converted to unsaturated sugars utilizing reagents such as silver fluoride [79]. One early example, shown in Scheme 6.44, applies this chemistry to a glucose derivative. 

In attempts to prepare the 2-benzyl-2-phenylhydrazone (29) of 3,5-di-O-benzoyl-2-deoxy-n-eryribose derivative), the unsaturated hydrazone (30) was obtained. ... 

The reaction of epoxides of carbohydrates with methylmagnesium iodide gives mainly deoxyiodo alcohols which, on p-toluenesulfonylation, afford derivatives []for example, methyl 4,6-0-benzylidene-3-deoxy-3-iodo-2-0-p-tolylsulfonyl-a-D-glucoside (74), prepared from methyl 2,3-anhydro-4,6-0-benzylidene-at-D-allopyranoside ] which imdergo ready elimination when treated with sodium iodide in acetone (Route A). The general applicability of this route to unsaturated compounds has been noted, and, in the pentose series, it has been applied to the preparation of methyl 4-0-benzyl-2,3-dideoxy- 3-L-glj/cero-pent-2-enoside (79). Here, the elimination occurs much... 

With the pentoses and 6-deoxyhexoses, from which pyranoid compounds analogous to (149) cannot be formed, both the saturated, and unsaturated, acyclic products have been isolated from reaction mixtures. For example, L-rhamnose, affords, on oxidation with peroxypropionic acid in aqueous dioxane, the crystalline, simple sulfone and unsaturated... 

The acetate 211a reacts in 5 minutes at —70° to give 3,4,6-tri-O-acetyl-2-deoxy-a-D-arabino-hexopyranosyl fluoride (212a), and after 24 hours at —70°, likewise by way of the unsaturated ion 215a, to the ion 216a. The high stability of the ions of type 216 is also evident in the pentose series. Thus, compounds 220, 221, 223, and... 

It was furthermore reported that reduction of the unsaturated deoxyhexopyranuronate degradation product (54) with sodium borohydride gives an epimeric mixture of the corresponding 3-deoxyhexonic acids (56 and 57). Ruff degradation of this mixture of compounds results in 2-deoxy-L- /ifeo-pentose (58). 

The unsaturated oligosaccharides (65) obtained in the j8-eliminative process of Preiss and AshwelP were cleaved enzymically, and accumulation of 4-deoxy-L-eryfhro-hex-4-enopyranuronate (66) was observed. The existence of the two tautomeric 3-deoxyhexulosonates (66 and 67) was established analytically and by conversion (through a two-step procedure by way of 68 and 69) into 2-deoxy-n-ery hro-pentose (70). 

It is known that deamination of some readily available amino acids can be performed with nearly quantitative retention of configuration. Based on this conversion, Yamada and co-workers elaborated an ingenious synthesis of o-ribose and D-lyxose starting from L-glutamic acid. The preliminary communication of this work was reported in the first volume of Ais series.Now the full details have been published. In an extension of the application of the unsaturated intermediate (399) for the synthesis of other pentoses, all 2,3-anhydro derivatives (400-403) were prepared. LAH-Reduction of -D-ribo and o-D-lyxo epoxides (400 and 401) afforded, after acetylation, 3-deoxy-pentosides 404 and 405, whereas the same reaction conditions converted fi-D-lyxo a-D-ribo epoxides (402 and 403) into the corresponding 2-deoxy-derivatives (406 and 407). 

Condensation of syn- or anti-27 with hydrazine afforded new pyrazole derivatives 28 with a stereodefined and protected amino diol side chain [64]. The preparation of push-pull substituted unsaturated monosaccharide derivatives and their use in the synthesis of nucleoside analogs have been reviewed [65]. Thus, the 2-formyl pentose glycals were transformed to the corresponding acyclo-C-nucleosides 29 [66]. Similarly, the benzy-lated 2-formylglycals reacted with hydrazine derivatives to afford the substituted l,2,4-tri-0-benzyl-lC-(lH-pyrazol-4-yl)-D-tetritols the deprotection of which was achieved with Pd/H2 to yield the lC-( 1-methyl-lH-pyrazol-4-yl)-D-tetritols [67]. 3-0-Benzyl-6-deoxy-l,2-0-isopropylidene-o -D-xylo-hept-5-ulofuranurono-nitrile was reacted with f, N-dimethylformamide dimethyl-acetal in THF to furnish the (E)-3-0-benzyl-6-deoxy-6-dimethyl-aminometh-ylene-l,2-0-isopropylidene-Q -D-xylo-hept-5-ulofuranurono-nitrile as a major product, and on treatment with carbon disulfide and methyl iodide under basic conditions afforded 3-0-benzyl-6-deoxy-l,2-0-isopropylidene-6-[bis(methylsulfanyl)methylene]-a-D-xylo-hept-5-ulofuranurono-nitrile. Further reaction with hydrazines yielded the reversed pyrazole-C-nucleoside analogs [68]. 

Reactions of 2-formyl-galactal, presented as an unsaturated sugar derivative with push-pull functionalization, with guanidinium and amidinium salts, respectively were carried out imder basic conditions to furnish the substituted 5-( 1,2,4-tri-O-benzyl-D-lyxo- l,2,3,4-tetrahydroxy-butyl)pyrimidines 92 (Fig. 16). Treatment of the 2-formyl pentose glycals with 2-aminobenzimid-azole and 3-amino-1,2,4-triazole, respectively afforded 3-(l,2,4-tri-0-benz-yl-D-lyxo-l,2,3,4-tetrahydroxy-butyl)benzo[4,5]imidazo[l,2-a]pyrimidine 94... 

This reaction was first reported by MacDonald and Fischer in 1952. It is the degradation of hexoses into pentoses involving the steps of formation of dithioacetal, oxidation to unsaturated disulfone by means of perphthalic acid, hydrazine treatment, and benzalde-hyde splitting of the corresponding hydrazone. Therefore, the whole process is known as the MacDonald-Fischer degradation. In addition, when the unsaturated disulfone is dissolved in aqueous ammonia or methanol saturated with ammonia, 2-deoxy-2-amino sugar is resolved. This reaction in combination with mass spectroscopy was used to study the structure and stereochemistry of carbohydrates. ... 

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