Ribose 5-phosphate, preparation

In RNA these bases are attached to the ribose phosphate chain as shown in Figure B. Synthetic polynucleotides can be produced that are like RNA in every respect except that they contain only one of the four bases they are called Poly A, Poly C, and Poly U. Poly G unfortunately cannot be prepared in high molecular weight form hence Poly I (in which the guanine amino groups have been removed) is prepared instead. 

Histidine can be prepared from imidazole as in Scheme 117. It is a basic amino acid, the biosynthesis of which appears to involve adenosine 5 -phosphate, ribose phosphate and glutamine (which supplies a nitrogen for the imidazole ring) (Scheme 118). Histidine is one of the most important amino acids and has involvement in such biological processes as ester hydrolysis, acylation and (by virtue of its complexing power with iron) oxygen... 

Following an 80 min reaction, ribose/phosphate buffer mixtures were rapidly cooled to 25 C, treated with o-phenylenediamine and incubated at 50 C for 30 min. Quinoxalines and unreacted OPD were extracted and concentrated for GC/MS analysis or separation by preparative TLC. Volatile quinoxaline and methylquinoxalines were identified by Rt and MS of available standards. 2-Ethylquinoxaline was tentatively identified by its MS alone. Non-volatile quinoxalines were isolated by preparative TLC and tentatively identified through literature Rf, NMR and UV data. Addition of OPD at die start of ribose/phosphate buffer reactions produced somewhat higher yields of the same quinoxalines in a similar ratio. No evidence for quinoxaline products was found in control experiments run in bis-tris buffer. 

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... 

Mlotkowska, B., Tropp, B.E., and Engel, R., The preparation of methyl 5-deoxy-5-(dihydroxyphosphinoyl)hydroxymethyl-2,3-0-isopropylidene-fS-D-ribofuranoside, a precursor to a hydroxymethylene analog of D-ribose 5-phosphate, Carbohydr. Res., 117, 95, 1985. 

The sugar configuration about the T, 2, 3, and 4 positions can be changed by synthesis. A variety of pyrimidine nucleoside cyclic phosphates have been made. Ukita et al. (425) prepared -D-lyxo-uridine 2 3 -cyclic phosphate (Fig. 21a). The configuration about the 2 and 3 positions is inverted and the two OH groups are now cis to the base rather than trans as in the D-ribose series. No hydrolysis at all of this compound was observed in the presence of RNase. However, both the cyclic phosphate and the free 2 (3 )-nucleotides inhibit the enzyme. The... 

For preparative applications, the expensive and configurationally unstable donor 128 can be simply prepared in situ by the action of ribose 5-phosphate isomerase (EC 5.3.1.6) on D-ribose 5-phosphate (39). This technique was applied to the stereoselective synthesis of d-[1-13C] fructose 6-phosphate 38 from [13C] formaldehyde [376,377] which also included a second enzymatic isomerization of the D-arafrino-3-hexulose 6-phosphate intermediate 129 into the more stable 2-hexulose derivative 38. Notable are the conflicting demands for high substrate levels (necessary to shift the fully reversible multi-component equilibrium) versus the notorious enzyme inactivation that occurs at higher formaldehyde concentrations. 

Some phosphoric acid derivatives of 2-desoxy-D-ribose have been obtained by enzymic methods of preparation. A reaction analogous to the phosphorolysis of glycogen to D-glucose 1-phosphate241 has been effected with either hypoxanthine- or guanine-D-riboside, both of which could be split by enzymic phosphorolysis with the formation of D-ribose 1-phosphate.242 The successful conclusion of these experiments prompted similar investigations with desoxyribonucleosides. 

Manson and Lampen243 reported that they obtained the phosphorolysis and arsenolysis of hypoxanthine desoxyriboside by enzyme preparations from calf-thymus gland and rat liver. An acid-stable phosphate ester was isolated as a product of phosphorolysis. Results to be outlined suggested that this ester was 2-desoxy-D-ribose 5-phosphate and evidence was obtained for its formation by a mutase type reaction from 2-desoxy-D-ribose 1-phosphate. This evidence was extended and reinforced when Manson and Lampen244 obtained indications for the formation of desoxy-D-ribose 1-phosphate during the phosphorolysis of thymidine. Consequently the conversions outlined may be depicted as shown. 

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