D,L-Ribose

D-Ribose, L-ribose and D,L-ribose crystallize without water of hydration. The melting point of the optically active forms is recorded by most authors as 86-87°2,33 37 39 although Alberda van Ekenstein7 reported a value of 95° for D-ribose. D,i>Ribose, prepared by crystallizing a mixture of equal parts of the enantiomorphs, melts at 83-84°.44 The optical crystallographic properties of D-ribose have been measured by... 

In the presence of formaldehyde (0.5 mol equiv.), sugar phosphates were formed in up to 45% yield, with pentose-2,4-diphosphates dominating over hexose triphosphates by a ratio of 3 1 (Scheme 13.2, Route B). The major component was found to be D,L-ribose-2,4-diphosphate with the ratios of ribose-, arabinose-, lyxose-, and xylose-2,4-diphosphates being 52 14 23 11, respectively. The aldomerization of 2 in the presence of H2CO is a variant of the formose reaction. It avoids the formation of complex product mixtures as a consequence of the fact that aldoses, which are phosphorylated at the C(2) position, cannot undergo aldose-ketose tautomerization. The preference for ribose-2,4-diphosphate 5 and allose-2,4,6-triphosphate formation might be relevant to a discussion of the origin of ribonucleic acids. 

A description of an amplification procedure based on the different solubility of the D-enantiomer and that of the corresponding d, L-racemate of ribonucleosides follows. When the melting points and solubilities of crystalline d, L-ribonucleosides and the pure D-ribonucleoside were determined, it was found that solution-based amplification of a slight ee of D-cytidine and D-adenosine, in a mixture with the d, L-racemates, is sufficiently large to produce solutions with at least 99% ee of the D-enantiomer (Breslow et al. 2010 and references cited therein). The 96% excess of D-uridine could also be sufficient to allow for the selection of the d isomer in solution under prebiotic conditions. In contrast, d, L-ribose itself forms a solid solution and d, l-guanosine a conglomerate (Breslow et al. 2010). This work is based on the mechanism for the amplification of fluctuations in racemic mixtures of the corresponding compounds (Morowitz 1969). 

Aldopentoses have three chirality centers and a total of 23 = 8 possible stereoisomers, or four d,l pairs of enantiomers. These four pairs are called ribose, arabinose, xylose, and lyxose. All except lyxose occur widely. r>Ribose is an important constituent of RNA (ribonucleic acid), t-arabinose is found in many plants, and D-xylose is found in wood. 

With the same synthetic sequence, labeled ribose molecules produced AIRs labeled on the ribose moiety. From D-erythrose and (l3C)NaCN, the Fischer-Kiliani synthesis, as modernized by Serianni et al.59 produced D-(l-l3C)ribose and D-(l-l3C)arabinose. The labeled arabinose was transformed into D-(2-l3C)ri-bose in the presence of dioxobis(2,4-pentanedionato)-0-0 -molybdenum(VI) in... 

Although small proportions of other products are formed when D-xylose is exposed to rather high acid concentrations, arabinose, lyxose, and ribose form considerably more of alternative products (generally reductic acid) than of 2-furaldehyde under these conditions. Reductic acid (2,3-dihydroxy-2-cyclopenten-l-one, 47) has been detected as a product after acid exposure of D-xylose or its major dehydration product, 2-furalde-hyde. Further work performed with D-[l- C]xylose and [a- C]2-fural-dehyde showed that reductic acid having identical label distribution was obtained from both starting materials. This indicated that a common primary source was involved, probably 2-furaldehyde, as it is readily formed from D-xylose under acidic conditions. 

Labeling experiments with l-deoxy-l-(dibenzylamino)-D-[l- C]-aruI>-mo-2-hexulosuronic acid [l- C] 112 indicated that the C label corresponded to the 5-methyl group of 111 (see Ref. 234). This is also consistent with a l-deoxy-2,3-dicarbonyl intermediate (115), and indicates that 111 is a decarboxylation product (see Scheme 22). The precise step entailing decarboxylation has not yet been determined. The carboxyl group could be carried through to ring closure (furanone formation). Such a step would provide a 2-carboxylate which is a /3-keto acid subject to ready decarboxylation. The labeling information and the initial steps of the mechanism in Scheme 22 are also consistent with the formation of 111 from D-[l- C]ribose and a secondary amine. ... 

The legioselectivity of electrophilic additions of the C=C double bond in 7-oxabicyclo[2.2.1]hept-5-en-2-yl (7-oxanorbom-5-en-2-yl) derivatives depends on the nature of the substituents at C(2). The adducts so-obtained can be transformed into the corresponding 5,6-disubstituted 7-oxanorboman-2-ones, which can be mono-substituted at C(3) stereoselectively, giving products with the same stereochemical information as hexoses. Thus, optically pure 7-oxanorbom-5-en-2-yl derivatives can be viewed as "naked sugars" Applications to the total, asymmetric syntheses of L-daunosamine, 2-deoxy-L-fucose, D- and L-aUose, D- and L-talose, D- and L-ribose,... 

Total Synthesis of D- and L-AUose, D- and L-Talose and of D- and L-Ribose Derivatives... 

L-Ribose is quite rare and the only practical method for its preparation is the transformation of L-arabinose by the method of Austin and HumoUer (4 steps, 9.5 % overall yield). L-Ribose has also been derived from, 2,3-<9-isopropylidene-L-glyceraldehyde, (5 steps, 12 %) after separation from a mixture containing L-arabinose. In Scheme 7 we summarize our total syntheses of D- and L-ribose derivatives using the " naked sugars" 32 and 38, respectively." Ketone 138 (Scheme 4) was oxidized into the corresponding lactone (-)-158 with MCPBA in 98 % yield. Treatment with anhydrous methanol, 2,2-dimethoxypropane and a small amount of methanesulfonic acid afforded the methyl 5-deoxy-D-allonate (-)-I59... 

D- and L-Ribose are synthesized starting from 2,3-0-isopropylidene-D-and L-glyceraldehyde, respectively, by the application of this reaction (2). 

The utility of these metallated 2-allyloxybenzimidazoles was demonstrated further through a synthesis of both d- and L-ribose (81CL1005). The allylcadmium derivative (551) reacted with 2,3-O-isopropylidene-D- and -L-glyceraldehyde to form the corresponding ribo-5-hexenitols (554) with high regio- and stereo-selectivity. Conversion of these products through their oxiranes to d- and L-ribose (557) required only a few additional manipulations as shown in Scheme 122. 

The exo/endo (99 1) adducts are of 90-92% optical purity. The enantiomeric bicyclic ketones can be transformed into carbohydrates in a few, stereochemically well-defined steps. In this way, derivatives of d- and L-ribose [38], L-allose, L-talose, and such [39] have been obtained. 

Exercise 15-15 How can D-glucose, D-fructose, and D-ribose be considered products of the addition of an alcohol to the carbonyl group of an aldehyde or ketone Name each of the carbonyl compounds by the IUPAC system. For the ribose carbonyl structure, determine the configuration at each chiral center, using the D,L system. 

Deoxy-D-ribose, AE75 2-Deoxy-L-ribose, AE76 Di-N-acetamide, AD07 Diacetic acid diselenide, AC90 Diacetone alcohol, AI00 2-Diacetoxymethyl-5-ni trofuran,... 

It is well known that if there is over-hydrolysis in the Feulgen test, the intensity of the color developed is much reduced. Lately, renewed interest in this effect has led to several interpretations being forwarded.69 81 82 The work of Stacey and his coworkers on the properties and reactions of desoxy-pentoses and -hexoses and in particular of 2-desoxy-D- and -L-ribose, indicates that over-hydrolysis of the nucleic acid not only brings it into a more diffusible form, but also changes the desoxypentose... 

A series of similar changes was observed on treatment of 2-desoxy-D-galactose with ethanolic hydrogen chloride and it was possible to prepare ethyl 2-desoxy-a/8-D-galactofuranoside and ethyl 2-desoxy-aj8-D-galacto-pyranoside. Essentially similar results were observed with desoxy-pentoses, and the methyl glyco-furanosides and -pyranosides of 2-desoxy-L-ribose were prepared.141... 

Hirashita, T. Kamei, T. Horie, T. Yamamura, H. Kawai, M. Araki, S. Preparation of y-het-erosubstituted allylindium and diindium reagents and their reactions with carbonyl compounds./. Org. Chem. 1999, 64,172-177. Yamaguchi, M. Mukaiyama, T. The stereoselective synthesis of d- and L-ribose. Chem. Lett. 1981, 1005-1008. 

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