Ribonucleoside structure

Conversion of purines, their ribonucleosides, and their deoxyribonucleosides to mononucleotides involves so-called salvage reactions that require far less energy than de novo synthesis. The more important mechanism involves phosphoribosylation by PRPP (structure II, Figure 34-2) of a free purine (Pu) to form a purine 5 -mononucleotide (Pu-RP). 

Complete confirmation of the structures assigned to the ribonucleosides has been provided by a study of their 5-0- p -tolylsulfonyl derivatives. Whereas 2,3-O-isopropylideneuridine and 2,3-O-isopropylideneinosine give 5-p-tolylsulfonyl derivatives which, with sodium iodide, are converted to 5-deoxy-5-iodo compounds,30 31 the corresponding adenosine and cytidine... 

Tipson devoted most of his years in Levene s laboratory accomplishing seminal work on the components of nucleic acids. To determine the ring forms of the ribose component of the ribonucleosides he applied Haworth s methylation technique and established the furanoid structure for the sugar in adenosine, guanosine, uridine, and thymidine. He showed that formation of a monotrityl ether is not a reliable proof for the presence of a primary alcohol group in a nucleoside, whereas a tosyl ester that is readily displaced by iodide affords clear evidence that the ester is at the 5-position of the pentofuranose. Acetonation of ribonucleosides was shown to give the 2, 3 -C -isopropyl-idene derivatives, which were to become extensively used in nucleoside and nucleotide chemistry, and were utilized by Tipson in the first chemical preparation of a ribonucleotide, inosinic acid. 

Ultraviolet (UV) spectroscopy does not tend to be the method of choice for structure determination, but a list of UV absorptions was given in the review by Knowles <1996CHEC-II(7)489>. Fluorescence properties and triplet yields of [l,2,3]triazolo[4,5-r/ pyridazines in various solvents have been reported <2002JPH83>. These heterocyclic systems were found to be photochemically very stable. In a recent paper, Wierzchowski et al. studied the fluorescence emission properties of 8-azaxanthine ([l,2,3]triazolo[4,5-r/ pyrimidine-5,7-dione) and its A -alkyl derivatives at various pH s <2006JPH276>. For the 8-azaxanthines, an important characteristic of emission spectra in aqueous solutions was the unusually large Stokes shift. Since 8-azaxanthine is a substrate for purine nucleoside phosphorylase II from Escherichia coli, the reaction is now monitored fluorimetrically. The fluorescence properties of [l,2,3]triazolo[4,5-r/ -pyrimidine ribonucleosides were earlier described by Seela et al. <2005HCA751>. 

Compounds based on the purine structure are classified as purines. Adenine is one of the two purines found in DNA and RNA. The other is guanine. Adenine and guanine are called bases in reference to DNA and RNA. A nucleic acid base attached to ribose forms a ribonucleoside. Adenine combined with ribose produces the nucleoside adenosine. When an oxygen atom is removed from the second carbon of ribose, the sugar unit formed is... 

Fig. 7.1.1 Structure of the naturally occurring purine (deoxy)ribonucleosides and nucleoside bases...

Figure 8-4 gives the structures and names of the four major deoxyribonucleotides (deoxyribonucleo-side 5 -monophosphates), the structural units of DNAs, and the four major ribonucleotides (ribonucleoside 5 -monophosphates), the structural units of RNAs. Specific... 

The structures of some modified nucleosides found in tRNA. The parent ribonucleosides are shown on the left in yellow screens. The other bases found in RNA result from post-transcriptional modification. 

In conclusion, a novel type of antineoplastic compounds, substituted 6-phenylpurine ribonucleosides, has been discovered. In our view, the cytostatic activity of this class of compounds cannot be deduced from any known cytostatic nucleoside or purine derivatives, and therefore, it might be considered a new structural lead in the search for antitumor compounds. 

Determination of the ring structure of the pyrimidine ribonucleosides, uridine and cytidine, as being furanoid was accomplished by Levene and... 

The syn and anti conformations of pyrimidine ribonucleosides have an opposite sign for certain transitions (e.g., the B2u transition) (67B843 69JA831 71JA(93)1600 72JCP2736 72MI3). Such relations are empirical correlations, since the molecular structures are too complicated to allow theoretical calculations of the rotational strengths. A combination of DNMR, CD spectroscopy, and molecular mechanics calculations has been applied to derivatives of indole 77 and thiazoline-2-thione 78 substituted by chiral rotors (Scheme 58). In these molecules the rotor adopts one of the bisected... 

Of considerable interest in relation to the results of Linschitz Connolly was the subsequent finding of Wolfenden et al. 161) that the photochemical adduct of methanol to purine ribonucleoside is a potent inhibitor of adenosine deaminase, in large part because of its structural resemblance to the presumed transition state intermediate involved in the deaminase reaction. 

The ribonucleosides that make up ribonucleic acid (RNA) are composed of D-ribose (a sugar) and four heterocyclic bases. The general structure of a ribonucleoside is... 

These four bases are incorporated into deoxyribonucleosides and deoxyribonucleotides similar to the bases in ribonucleosides and ribonucleotides. The following structures show the common nucleosides that make up DNA. The corresponding nucleotides are simply the same structures with phosphate groups at the 5 positions. 

Within the structure of the nucleic acids, a pyrimidine or purine is linked to the sugar (2-deoxy-D-ribose or D-ribose) to give a nucleoside. The nucleosides are referred to as deoxyribonucleosides if they contain deoxyribose, and ribonucleosides if they contain ribosc. The purine nucleosides have a (3-glycosidic linkage from N-9 of the base to C-l of the sugar. In pyrimidine nucleosides, the linkage is from N-l of the base to C-l of the sugar. 

Write the structures of (a) the ribonucleoside containing adenine and (b) the deoxyribonucleoside containing cytosine. 

Cytokinins are unique among plant hormones in that adenine compounds of identical structure occur in nucleic acids. More specifically, particular cytokinin-active ribonucleosides occur as components of certain molecular species of tRNA. Zachau et al. (19), during the determination of the base sequences of serine tRNA in yeast, first reported an "odd" base immediately adjacent to the 3 end of the anticodon. In collaboration with Biemann et al. (20), this "odd" base was identified as the natural cytokinin isopentenyl-adenosine, which is one of the most highly active cytokinins known. 

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