Purines types

Adenine phosphoribosyltransferase (APRT) deficiency is an inherited disorder of purine metabolism and is inherited in an autosomal recessive manner (K18, V7). This enzyme deficiency results in an inability to salvage the purine base adenine, which is oxidized via the 8-hydroxy intermediate by xanthine oxidase to 2,8-di-hydroxyadenine (2,8-DHA). This produces crystalluria and the possible formation of kidney stones due to the excretion of excessive amounts of this insoluble purine. Type I, with virtually undetectable enzyme activity, found predominantly in Caucasians, is found in homozygotes or compound heterozygotes for null alleles. Type II, with significant APRT activity, found only in Japan, is related to a missense mu-... 

The coordination chemistry of the purine-type ligands has been studied on a rather large scale during the last decade, due to its relevance in biological systems. Detailed reviews are available of the coordination chemistry aspects both in the solid state and in solution.146-149 Recently it has also been proposed that the role of metal-ion binding to purines influences the conversions between, for example, B-DNA and Z-DNA.150... 

The structural components of nucleic acids. Nucleic acids are long linear polymers of nucleotides, called polynucleotides, (a) The nucleotide consists of a five-carbon sugar (ribose in RNA or deoxyribose in DNA) covalently linked at the 5 carbon to a phosphate, and at the 1 carbon to a nitrogenous base. (b) Nucleotides are distinguished by the types of bases they contain. These are either of the two-ring purine type or of the one-ring pyrimidine type. 

In the crystal structures, homo base pairs with centrosymmetrical configuration are favored. This general statement is true for all the four different bases of pyrimidine and purine type. The individual bases exhibit considerable dipole moments, as shown in Thble 16.1, and we assume that the preference for base pairs with a center of symmetry is due to the antiparallel orientation of the dipole moments in this particular arrangement. This results in a favorable cancellation of the total electric field over the crystal volume. 

Differences between the two sets of pairs of the four isomeric purine types also arise from magnetic circular dichroism measurements of the four A/ methylpurines (73JHC419). Thus the MCD bands for the 1-Me and 3-Me forms are of lower intensity and occur at shorter wavelengths than the related bands for the 7-Me and 9-Me isomers. Also protonation results in wavelength shifts and changes in peak intensities and these variations could be used to characterize a particular isomer. Thus peak heights of the bands for the 1-Me and 3-Me isomers after protonation increase by 0.25 and three times whereas those for the 7-Me and 9-Me isomers decrease by 0.25 and three times, respectively. 

One of a number of basic compounds found in living matter and having a purine-type molecular structure. See adenine base pair guanine hypoxanthine xanthine uric acid caffeine theobromine. 

A CBP in pea thylakoid membranes has been identified by photoaffinity labeling with a urea-type cytokinin [50]. The membrane protein (Thy46) has a relatively low affinity of about 1 xM for urea type cytokinins which may be explained by the procedures used to solubilize the protein. Like CSBP, its affinity is weaker for purine-type than urea-type cytokinins. Nonetheless, Thy46 can discriminate enantiomers of benzyladenine (BA), binding R-MeBA, an active cytokinin, and not S-MeBA which has no cytokinin activity. 

This nucleotide has the structure of AMP except that N7 is replaced by a CH unit (see Figures 5 and 10) and this exchange transforms this purine-type nucleotide into one with pyrimidine-type properties vide infra). 

Azaindole is structurally close to purine and provides a simplified model for possible proton-relay for purine-type nucleobases. The mobile proton can stay either on the pyrrole or on the pyridine nitrogen. Theoretical calculations using the 6-31G(d) basis set predicted that the tautomer with the pyrrole hydrogen is more stable by 13-16 kcal mol than the structure with a pyridine hydrogen [74,... 

Ai,A/-bis(hydroxymethyl) formamide [6921-98-8] (21), which in solution is in equiUbrium with the monomethylol derivative [13052-19-2] and formaldehyde. With ben2aldehyde in the presence of pyridine, formamide condenses to yield ben2yhdene bisformamide [14328-12-2]. Similar reactions occur with ketones, which, however, requite more drastic reaction conditions. Formamide is a valuable reagent in the synthesis of heterocycHc compounds. Synthetic routes to various types of compounds like imida2oles, oxa2oles, pyrimidines, tria2ines, xanthines, and even complex purine alkaloids, eg, theophylline [58-55-9] theobromine [83-67-0], and caffeine [58-08-2], have been devised (22). 

Simidzu et al.70) carried out template-directed synthesis using various types of templates, e. g neutral ones, 34 (PSt TCT) and PSt TCTC, and cationic ones, such as APVP, 35 (APVP PSt), UPVP PSt, ARPVP, APEI, and 36 (ARPEI). They obtained a large amount of purine-containing oligomers (dimer or trimer) as compared to pyrimidine ones by condensation of nucleotide mixture in the presence of the neutral templates containing pyrimidine bases, such as PSt TCT and PSt TCTC. The authors stated from the results that the existence of the... 

There are important inhibitory systems built into the control of events following C-fibre stimulation. Thus, during peripheral noxious stimulation, spinal mechanism, driven by NMDA-receptor-mediated activity, can become active to damp down further neuronal responses, the purine, adenosine (see Chapter 13), appears to be involved in this type of control and has been reported to be effective in humans with neuropathic pain. It is thought that the depolarisations caused by activation of the NMDA receptor increase the metabolic demand on neurons and so ATP utilisation increases. ATP then is metabolised to adenosene and the purine then acts on its inhibitory Ai receptor in the... 

Nucleobases, including 9-methyl-, 9-ethyl-, 1,9-dimethyl-guanine and 2-amino-6-methoxy-9-methylpurine, form complexes of the type Au(N)Cl3 when reacted with [AuCU] in water at pH 3—4. Binding of a AuCh unit to the N (7) position of the purine ring was confirmed by X-ray crystallography [26]. 

The formation of three-stranded nucleic acid complexes was first demonstrated over five decades ago [56] but the possible biological role of an extended triplex was expanded by the discovery of the H-DNA structure in natural DNA samples [57-59]. H-DNA is an intermolecular triplex that is generally of the pyrimidine-purine x pyrimidine type ( dot -Watson-Crick pairing and cross Hoogsteen base paring) and can be formed at mirror repeat sequences in supercoiled plasmids [59]. 

Balzarini J, Perez-Perez M-J, San-Felix A, Velazquez S, Camarasa M-J, De Clercq E. [2, 5 -Bis-0-(tert-Butyldimethylsilyl)]-3 -spiro-5"- [4"-amino-1",2"-oxathiole-2",2"-dioxide) (TSAO) derivatives of purine and pyrimidine nucleosides as potent and selective inhibitors of human immunodeficiency virus type 1. Antimicrob Agents Chemother 1992 36 1073-1080. 

However, the biochemical significance of the latter studies is challenged by the fact that the transformation of transient purine and pyrimidine radicals into diamagnetic decomposition products is oxygen-independent in the solid state. Therefore, it is necessary to study the chemistry of one-electron nucleobase intermediates in aerated aqueous solutions in order to investigate the role of oxygen in the course of reactions that give rise to oxidation products within DNA and model compounds. In this respect, type I photo-... 

One-electron oxidation of the adenine moiety of DNA and 2 -deoxyadenos-ine (dAdo) (45) gives rise to related purine radical cations 46 that may undergo either hydration to generate 8-hydroxy-7,8-dihydroadenyl radicals (47) or deprotonation to give rise to the 6-aminyl radicals 50. The formation of 8-oxo-7,8-dihydro-2 -deoxyadenosine (8-oxodAdo) (48) and 4,6-diamino-5-formamidopyrimidine (FapyAde) (49) is likely explained in terms of oxidation and reduction of 8-hydroxy-7,8-dihydroadenyl precursor radicals 47, respectively [90]. Another modified nucleoside that was found to be generated upon type I mediated one-electron oxidation of 45 by photoexcited riboflavin and menadione is 2 -deoxyinosine (51) [29]. The latter nucleoside is likely to arise from deamination of 6-aminyl radicals (50). Overall, the yield of formation of 8-oxodAdo 48 and FapyAde 49 upon one-electron oxidation of DNA is about 10-fold-lower than that of 8-oxodGuo 44 and FapyGua 43, similar to OH radical mediated reactions [91]. 

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