Purines and nucleosides

Cleavage af nucleosides. Purine and pyrimidine bases can be cleaved from derivatives of adenosine, cytidine, and uridine by potassium r-butoxide in dioxane. 

Few of the nucleic acids present in barley are thought to survive malting and mashing. Their degradation products, the phosphorous-containing nucleotides (Table 22.13), nucleosides, purine and pyrimidine bases (Table 22.14) are present in beer. Guanosine, cytidine and uridine are the major constituents [88]. 

Liquid chromatography is a rapid, selective and sensitive technique which can be adapted to the analysis of extracts from a variety of biological sources. It constitutes an excellent method for the analysis of nucleotides, nucleosides, purines, and pyrimidines bases. 

E. Gerlach, R. H. Dreisbach, and B. Deuticke, Paper chromatographic separation of nucleotides, nucleosides, purines, and pyrimidines, J. Chromatog. 18 81 (1965). 

Hydrolysis of nucleic acids may lead to oligonucleotides, mononucleotides, nucleosides, purine and pyrimidine bases, sugar phosphates and free carbohydrates. Secondary products always result also, e. g., from deamination of the aminopurines and aminop3uimidines or their nucleosides and nucleotides. 

Purine and pyrimidine bases Nucleosides Nucleotides Nucleic acids... 

Acetylation of hydroxyl groups and esterification of carboxyl groups have been observed ia a limited number of cases but, ia geaeral, have ao preparative advantage over chemical methods. By comparison, phosphorylation has been useful ia the preparatioa of modified purine and pyrimidine mononucleotides from their corresponding nucleosides, eg, 6-thioguanosiae [85-31-4] (51) (97). 

Because aromatic purines and purine nucleosides and free purines such as hypo-xanthine and guanine 242 are readily silylated-aminated [64] (cf Scheme 4.24), it is obvious that 6-membered hydroxy-N-heterocycles are analogously silylated-aminated, with reactivity in the order given in Scheme 4.25 [73] X=OTf is the best leaving group and X=NHSiMe3 (cf the transamination as discussed in Section 4.2.4) is the weakest. 

Deoxy-5 -fluoroadenosine (911) and the analogs 910, 912, 913 were prepared by coupling of 5-deoxy-5-fluoro-D-ribofuranose and 6-chloro-purine. 2, 5 -Dideoxy-5 -fluoroadenosine (914) was prepared through a displacement reaction of the corresponding 5 -0-tosyl precursor with fluoride (BU4NF in DMF). The carbocyclic nucleosides 915 and 916 have been prepared and their antiviral activities evaluated. 

The biosynthesis of purines and pyrimidines is stringently regulated and coordinated by feedback mechanisms that ensure their production in quantities and at times appropriate to varying physiologic demand. Genetic diseases of purine metabolism include gout, Lesch-Nyhan syndrome, adenosine deaminase deficiency, and purine nucleoside phosphorylase deficiency. By contrast, apart from the orotic acidurias, there are few clinically significant disorders of pyrimidine catabolism. 

Liver, the major site of purine nucleotide biosynthesis, provides purines and purine nucleosides for salvage and utilization by tissues incapable of their biosynthesis. For example, human brain has a low level of PRPP amidotransferase (reaction 2, Figure 34-2) and hence depends in part on exogenous purines. Erythrocytes and polymorphonuclear leukocytes cannot synthesize 5-phosphoribosylamine (strucmre III, Figure 34-2)... 

Fig. 44. Common sites for attaching redox- and photo-active groups to nucleosides C5 pyrimidine, C7-deaza-purine, and C8-purine.

In aqueous solution, caffeine associates to form at least a dimer and probably a polymer 12 the molecules are arranged in a stack.13 Caffeine will also associate with purines and pyrimidines either as the free bases or as their nucleosides.13 Caffeine crystallizes from water as a monohydrate [9],... 

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. 

A different strategy has been applied in our work, that emphasizes the importance of DNA stability on hole transfer within double-stranded DNA. This work is based on determination of the overall yield of oxidized nucleosides that arise from the conversion of initially generated purine and pyrimidine radical cations within DNA exposed to two-photon UVC laser pulses. On the one hand, this work benefits from the excellent current knowledge of chemical reactions involving the radical cations of DNA bases, and on the other hand, from major analytical improvements that include recent availability of the powerful technique of high performance liquid chromatography-electrospray ionization-tandem mass spectrometry (CLHP-ESI-MS/MS) [16-18]. 

Wang, J., et al. Functional and molecular characteristics of Na(+)-dependent nucleoside transporters. Pharm. Res. 1997, 14, 1524-1532. Ritzel, M. W., et al. Recent molecular advances in studies of the concen-trative Na+-dependent nucleoside transporter (CNT) family identification and characterization of novel human and mouse proteins (hCNT3 and mCNT3) broadly selective for purine and pyrimidine nucleosides (system rib). Mol. Membr. Biol. 2001, 18, 65-72. 

Mayer, E., Valis, L., Huber, R., Amann, N. and Wagenknecht, H. A. (2003). Preparation of pyrene-modified purine and pyrimidine nucleosides via Suzuki-Miyaura cross-couplings and characterization of their fluorescent properties. Synthesis 2335-2340. 

---