Purines isoguanines

Purines — These molecules have basic skeletons of purine heterocycles. Adenine and guanine, intrinsic components of nucleic acids, are also ubiquitous molecules. Related molecules are isoguanine, xanthine, and uric acid. 

This chemical procedure was found to be of general applicability and a large panel of purine derivatives, namely hypoxanthine 2, diaminopurine 3, xanthine 4, isoguanine 5 and guanine 6 were obtained from the imidazole intermediates in the presence of other one-carbon fragments such as cyanide and cyanogens (Scheme 2). 

Figure 8.7 Formation pathways of various purine derivatives (a) guanine, (b) hypoxanthine, (c) xanthine, (d) diaminopurine, (e) isoguanine, and (f) adenine...

The keto/enol or amino/imino equilibrium can be shifted, however, if the bases are chemically modified as in isoguanine (2-hydroxy,4-amino-purine). In this molecule, the tautomeric equilibrium depends largely on the dielectric constant of the solvent [525]. 

The naturally occurring purines fall into 4 main groups. (1) Simple substituted derivatives of purine (1) such as adenine (2) and various 6-AT-substituted derivatives. (2) Monoxo-dihydropurines such as hypoxanthine (3), guanine (4), and isoguanine (5). f3) Dioxotetra-hydropurines such as xanthine (6) and methylated derivatives including the 3,7-dimethyl derivative theobromine (7), 1,3-dimethylxanthine or theophylline f8), and 1,3,7-trimethylxanthine or caffeine (9). (4) Trioxohexahydropurines such as uric acid (10). 

Examples of all the four purine iV-oxides are known. Purine 1-oxide may be prepared from purine and perbenzoic acid over two weeks (62JOC567), and adenine 1-oxide is similarly prepared from adenine over 2 days (58JA2759). On the other hand hypoxanthine 1-oxide is best obtained by deamination of adenine 1-oxide (66JOC966). Reaction of 5-amino-4-hydroxyformamidinoimidazole with carbon disulfide may be used to make 2-thioadenine 1-oxide which with alkaline peroxide provides a useful route to isoguanine 1-oxide (67JOC1151). 

Purines show typical absorption spectra which are useful for the identification and the determination of their structure tautomeric equilibria can also be studied. By comparison of the spectra of natural and synthetic derivatives of purines, the N9 glycosylic linkage was established for nucleosides. The relatively simple spectra of purines show two main bands. Purine shows maxima around 220 nm and at 263 nm in neutral solution. Since the imidazole ring has no characteristic UV absorption, the spectra of purines and pyrimidines show similarities. Similar observations have been made for 7-deazapurines, 8-azapurines etc. In the series of adenine hypoxanthine, and xanthine (at pH 6) only one maximum is observed guanine, isoguanine, and purinc-2,6-diamine show two maxima. 

Since many purines exist in lactam and lactim forms the position and intensity of the peaks can be used for pH determination. The population of tautomers depends on the solvent and is strongly affected in some cases, e.g. for isoguanine or isoinosine. Table 15 summarizes UV data for selected purines with various substituents including nucleosides,... 

Activation of a chloro substituent is accomplished using purine A-oxides. Thus, 2-chloroad-enine 1-oxide gives isoguanine 1-oxide (9) when treated with acid or base. ... 

Groebke, K. et al. (1998). Why pentose- and not hexose-nucleic acids V. Purine-purine pairing in homo-DNA guanine, isoguanine, 2,6-diaminopurine, and xanthine. Helvetica Chimica Acta, 81, 375—474 (footnote 64 on p. 444). 

In 1932, Cherbuliez and Bernhard isolated, from croton beans (Croton tiglium L.), a purine nucleoside which they named crotonoside. It is isomeric with guanosine and gives, on acid hydrolysis, D-ribose and isoguanine. 9- 3-D-Ribofuranosylisoguanine (14), prepared by treatment of... 

Included here are the five plant bases, i. e., heteroxanthine, theophylline, theobromine, caffeine and tetramethyltrihydroxypurine, and the purines from the animal kingdom such as, e.g., adenine, hypoxanthine, guanine, vernine (guanosine), isoguanine, xanthine and uric acid. 

Figure 20. Within the purine family, not only adenine and guanine, but also hypoxanthine, isoguanine, 2,6-diamin(q)uiine and xanthine are potentially [Hebiological structures. Theiefcxe, the pairing properties of these bases must also be investigated in the context of the present study.

Strong purine-purine Watson-Crick pairing between guanine and isoguanine... 

Amino-1,3-dihydro-2/f purin-2-one Isoguanine C5H5N5O 3373-53-3 151.127 >360 IHjO... 

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