Nomenclature purine

According to the systematic nomenclature these substances were first named l-f-triazolo[d] pyrimidines in compliance with the general principles of the Ring Index/ More recent papers and Chemical Abstracts indexes use the term i -triazolo[4,5-d]pyrimidine (147) in accord with the lUPAC nomenclature. The numbering of substituents when using the last-mentioned name is different from that of the 8-aza analogs. For the formulas of oxygen and sulfur derivatives names derived from the lactim or thiolactim form are almost exclusively in use (in common with the purine derivatives). These derivatives are thus described as hydroxy and mercapto derivatives, respectively. The name 1,2,3,4,6-pentaazaindene is used only rarely for this system. 

Both purine and pteridine are parent heterocycles for nomenclature purposes. The systematic procedure for naming fused heterocycles is an extension of that we saw in Section 11.8 where we considered a benzene ring fused to a heterocycle. The main difference is that we have to identify bonds in two... 

Bases, Nucleosides, and Nucleotides. The relationship of these components of a nucleic acid or polynucleotide is shown in Chart 10. The numbering of the pyrimidine (uracil) and the purine (adenine) shown is the IUPAC nomenclature used by Chemical Abstracts, and... 

Both DNA and RNA contain two major purine bases, adenine (A) and guanine (G), and two major pyrimidines. In both DNA and RNA one of the pyrimidines is cytosine (C), but the second major pyrimidine is not the same in both it is thymine (T) in DNA and uracil (U) in RNA Only rarely does thymine occur in RNA or uracil in DNA The structures of the five major bases are shown in Figure 8-2, and the nomenclature of their corresponding nucleotides and nucleosides is summarized in Table 8-1. 

The nomenclature for the minor bases can be confusing. Like the major bases, many have common names— hypoxanthine, for example, shown as its nucleoside inosine in Figure 8-5. When an atom in the purine or pyrimidine ring is substituted, the usual convention (used... 

Although molybdenum and tungsten enzymes carry the name of a single substrate, they are often not as selective as this nomenclature suggests. Many of the enzymes process more than one substrate, both in vivo and in vitro. Several enzymes can function as both oxidases and reductases, for example, xanthine oxidases not only oxidize purines but can deoxygenate amine N-oxides [82]. There are also sets of enzymes that catalyze the same reaction but in opposite directions. These enzymes include aldehyde and formate oxidases/carboxylic acid reductase [31,75] and nitrate reductase/nitrite oxidase [83-87]. These complementary enzymes have considerable sequence homology, and the direction of the preferred catalytic reaction depends on the electrochemical reduction potentials of the redox partners that have evolved to couple the reactions to cellular redox systems and metabolic requirements. 

More recently, Bayer disclosed potent, selective PDE2 inhibitors in a series of patents (Figure 9.34) [121]. A key feature of these inhibitors, which belong to the substrate-analog series, is a benzylic rather than a phenylic substitution at position 2 (using the common numbering system of purine nomenclature) of the heterocycle. Thus, inhibitors 145 and 146 demonstrated moderate potency toward PDE2 and... 

CAS has fairly precise rules for denoting which structural systems are deemed to be tautomeric, and to which tautomer indexing is directed. In CAS nomenclature 1972-2006, tautomeric substances were often indexed under theoretical tautomers, e.g., the H- form of purines, which had no practical existence. CAS numbers for tautomeric substances therefore often referred to unknown tautomers. 

The system was first named by Fischer 0899CB435) but the correct ring structure was proposed much earlier <1875LA( 175)243) in a formula for uric acid. In the general literature purine nomenclature has been to a large extent affected by the abundance of trivial names for compounds which were isolated before their structures were known and by variation in description of tautomeric forms. 

The nomenclature of nucleotides and their constituent units was presented earlier (Section 5.1.2). Recall that a nucleoside consists of a purine or pyrimidine base linked to a sugar and that a nucleotide is a phosphate ester of a nucleoside. The names of the major bases of RNA and DNA, and of their nucleoside and nucleotide derivatives, are... 

Table 27-1 gives the nomenclature of purine and pyrimidine nucleosides and nucleotides. Names of purine nucleosides end in -osine, whereas those of pyrimidine nucleosides end in -idine guanine nucleoside is guanosine and should not be confused with guanidine, which is not a nucleic acid base thymidine is a deoxyriboside. 

Fig. 14 Atomic nomenclature of the purine nucleoside and phosphate nucleophile.

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