Of D-ribose

Generating Haworth formulas to show stereochemistry m furanose forms of higher aldoses is slightly more complicated and requires an additional operation Furanose forms of D ribose are frequently encountered building blocks m biologically important organic molecules They result from hemiacetal formation between the aldehyde group and the C 4 hydroxyl... 

Notice that the eclipsed conformation of d ribose derived directly from the Fischer pro jection does not have its C 4 hydroxyl group properly oriented for furanose ring forma tion We must redraw it m a conformation that permits the five membered cyclic hemi acetal to form This is accomplished by rotation about the C(3)—C(4) bond taking care that the configuration at C 4 is not changed... 

Conformation of D ribose suitable for furanose ring formation... 

FIGURE 25 5 Distribution of furanose pyranose and open chain forms of d ribose in aqueous solution as mea sured by H and NMR spectroscopy... 

The same kind of 5 3 phosphodiester units that join the 2 deoxy d ribose units m Figure 28 I are also responsible for connecting nucleosides of d ribose... 

DiaZepin Nucleosides. Four naturally occurring dia2epin nucleosides, coformycin (58), 2 -deoxycoformycin (59), adechlorin or 2 -chloro-2 -deoxycoformycin (60), and adecypenol (61), have been isolated (1—4,174,175). The biosynthesis of (59) and (60) have been reported to proceed from adenosine and C-1 of D-ribose (30,176,177). They are strong inhibitors of adenosine deaminase and AMP deaminase (178). Compound (58) protects adenosine and formycin (12) from deamination by adenosine deaminase. Advanced hairy cell leukemia has shown rapid response to (59) with or without a-or P-interferon treatment (179—187). In addition, (59) affects interleukin-2 production, receptor expression on human T-ceUs, DNA repair synthesis, immunosuppression, natural killer cell activity, and cytokine production (188—194). 

The numbering scheme used for nucleosides maintains the independence of the two strirctural units. The pyrimidine or purine is numbered in the usual way. So is the carbohydrate, except that a prime symbol ( ) follows each locant. Thus adenosine is a nucleoside of D-ribose, and 2 -deoxyadenosine is a nucleoside of 2-deoxy-D-ribose. 

Of the four possible 5-deoxy-pent-4-enofuranoses, the D-erythro-isomer was of interest as a potential source of derivatives of L-lyxofuranose. For this purpose, a vinyl ether having the D-en/ hro-configuration has been prepared from derivatives of D-ribose. Condensation of D-ribose with acetone in the presence of methanol, cupric sulfate and sulfuric acid at 30°C., as described by Levene and Stiller(30) afforded a sirupy product consisting mainly of methyl 2,3-O-isopropylidene-D-ribofuranose (40). Treatment of a pyridine solution of the sirup with tosyl chloride... 

What is the stereochemical relationship of D-ribose to L-xylose What generalizations can you make about the following properties of the two sugars ... 

Scheme 27.—A degradation of D-ribose, which allows the localization of radioactivity in each carbon atom.

In the two nucleic acids, the sugar component consists solely of D-ribose or D-deoxyribose. 

Administration203 to chicks of acetic acid labeled with C14 (in the carboxyl group) gave D-glucose (from the glycogen) labeled equally at C3 and C4, but the D-ribose (from nucleic acids) had more label at C3 than at C2, indicating that in vivo D-ribose does not arise exclusively from hexose by loss of Cl. The 20-30% isotope content of D-ribose formed from D-glucose-l-C14 by Escherichia coli indicates that direct conversion is the major pathway but that a part is probably derived from transketolase action.204 206... 

The above transketolase and transaldolase reactions were found inadequate to explain the metabolism of D-ribose 5-phosphate, because of the non-accumulation of tetrose phosphate, the 75 % yield of hexose phosphate, and the results of experiments with C14 (the distribution of which differed markedly from the values predicted for such a sequence). 24(b) Thus, with D-ribose-l-C14, using rat-liver enzymes, any hexose formed should have equal radioactivity at Cl and C3, whereas, actually, 74% appeared at Cl. Furthermore, D-ribose-2,3-Cl42 should have given material having equal labels at C2 and C4 in the resultant hexose, whereas, in fact, it had 50% of the activity at C4, C3 was nearly as active as C2, and Cl had little activity. Similar results were obtained with pea-leaf and -root preparations.24 The following reactions, for which there is enzymic evidence,170(b) were proposed, in addition to those involving D-aftro-heptulose, to account for these results.24(b) (o) 200... 

Hampton, A., Perini, F., and Harper, P.J., Derivatives of phosphonate and vinyl phosphate analogs of D-ribose 5-phosphate, Carbohydr. Res., 37, 359,... 

The reaction catalyzed by KDO 8-phosphate synthetase (reaction 2, Scheme 35) was first observed by Levin and Racker9 in extracts from Pseudomonas aeruginosa (see Scheme 1), and later by Ghalambor and Heath29 in extracts from Escherichia coli 0111 B4 and J-5. In the initial experiments of Levin and Racker,135 the fate of D-ribose 5-phosphate in crude bacterial extracts was studied, and the KDO 8-phosphate discovered by the authors is really derived from D-ribose 5-phosphate by three, sequential, enzyme-catalyzed reactions (see Scheme 36). 

Thio-D-ribose (Methanolysis) a-Pyranoside formed first followed by P-pyranoside then p-furanoside and oc-furanoside (furanosides only minor products) Mechanism probably quite different to that of D-ribose first step may be direct displacement at C-1 of the six-membered, sulphur-containing ring 20)... 

This enzyme [EC 5.4.2.7], also known as phosphodeoxy-ribomutase, catalyzes the interconversion of D-ribose 1-phosphate and D-ribose 5-phosphate. This enzyme will also catalyze the interconversion of 2-deoxy-D-ribose 1-phosphate and 2-deoxy-D-ribose 5-phosphate. The bisphosphate compound is the cofactor thus, D-ribose 1,5-bisphosphate, 2-deoxy-D-ribose 1,5-bisphosphate, or even a-D-glucose 1,6-bisphosphate. 

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