Oxopurines hypoxanthine

The predominant binding site in 9-substituted 6-oxopurines (guanine and hypoxanthine derivatives) is the N7 atom of the base (Figure 6). The prevailing keto tautomer requires proton at N1 even in mildly acidic conditions, which efficiently prevents platination of the N1 site [7]. Under neutral and basic conditions competition of Pt(II) between the N1 and N7 sites has been reported. Attachment of Pt(II) to the N7 atom acidifies the N1H proton and facilitates coordination of additional platinum ions to both N1 and N3 [7]. In N7,N9-blocked 6-oxopurines, the N1 site is the major coordination site [7,24],... 

With aquated Pt(II) compounds, numerous studies have revealed the kinetic preference of the 6-oxopurine N7 site [15,35]. In addition to the favorable electrostatic potential mentioned above [23] also steric factors seem to favor coordination to the guanine N7 site, in particular [36]. Estimated relative steric parameters (in parenthesis) suggest that the guanine N7 (1.00) and hypoxanthine N7 (1.03) atoms are the least sterically hindered binding sites in alkylated nucleobases, followed by the adenine N7 (1.17) and deprotonated hypoxanthine N1 (1.17) sites and the deprotonated N3 atoms of the different pyrimidine bases (1.39 for U, 1.44 for T, and 1.56 for C), while the adenine N1 (1.58) and... 

Purine-6-thione, in forming the 8-oxopurine, behaves like other 6-substituted purines108-108 used with this enzyme system. The exception to the rule is hypoxanthine which suffers attack at the... 

Differentiation of tautomers by the use of UV spectra has not been too rewarding. Thus whereas hypoxanthine almost certainly exists as the lactam form (13) as indicated by IR and other spectral studies, its UV absorption spectrum (Amax 249 nm, pH 5.6) is similar to that of 6-methoxypurine (Amax 252 nm, pH 5.2), a derivative of the lactim form of hypoxanthine, and l,7-dimethyl-6-oxo-l(if),6(if)-purine (43) (B-73MI40902), a definite lactam derivative. On the other hand, the UV spectrum of 8-oxo-7(H),8(/7)-purine (44) is closer to that of its 7- and 9-monomethyl and 7,9-dimethyl (oxo or lactam) derivatives than to 8-methoxypurine (45) (B-73MI40902) implying the oxo structure. Even in basic solutions where the lactim structure is expected, the results may be difficult to interpret. Thus the spectrum of the anion of hypoxanthine is similar to that of the neutral species of adenine, (Amax 258 and 260 nm, respectively) whereas this is not true of the 2- and 8-oxopurines when compared with the corresponding aminopurines. 

Bromopurines have also -been prepared from oxopurines and phosphoryl bromide. In this way 6-bromopurine was produced in 40% yield from hypoxanthine (56JA3508) but xanthine only furnished a low (10%) yield of 2,6-dibromopurine. 

Thioxo- and S-alkylthio-purines are readily converted into corresponding oxopurines with various reagents including oxidizing agents such as nitric acid (25-50%) which converts 6-thioxo-1,6-dihydropurine into hypoxanthine (65MI40906). More readily hydrolyzed sulfinic acids are likely intermediates in these reactions (74MI40902). 

A major route to thioxopurines involves thiation of the corresponding oxopurine. Thus a good yield of 6-thioxo-l,6-dihydropurine is obtained from hypoxanthine and phosphorus pentasulfide (61JA4038). Thiation of an appropriate diaminopyrimidine and concomitant cyclization to a thioxopurine is sometimes possible as in the preparation of 2-amino-l-methyl-6-thioxo-l,6-dihydropurine from 2,6-diamino-5-formamido-3-methyl-4-oxo-3,4-dihydropyrimidine and phosphorus pentasulfide in refluxing pyridine over 30 hours... 

Aminoimidazole-5(4)-carboxamides are the most common imidazole derived precursor molecules for oxopurines, such as hypoxanthine, xanthine, guanine, and isoguanine, using various condensation reagents. In particular, nucleosides are accessible by this route. 

Purine 77-oxides, when exposed to UV, y, or X-radiation, can be reduced to the parent purine or rearranged to an oxopurine. For example, the anion of hypoxanthin-l-ol (1) is oxidized to xanthine (2) in aqueous solution upon irradiation, ... 

AI3-52242 1,7-Dihydro-6H-purin-6-one EINECS 200-697-3 HX 6-Hydroxypurine 6-Hydroxy-1H-purine Hypoxanthine Hypoxanthine enol NSC 14665 6-Oxopurine 3H-Purin-6-ol Purin-6-ol 9H-Purin-... 

Very little structural information is available for cadmium(II) complexes with neutral oxopurines. Nevertheless, the basicity of the N-donors in this kind of oxopurine ligand, as well as the softness, increases after the dissociation of at least one of the protons. Consequently, most of the available crystal data concerning complexes of such ligands refer to the tmivalent anions of hypoxanthine (Hhyp), xanthine (Hxan) or theophylline (Htheo). Neutral hypoxanthine yields the compound [Cd2(p2-N3,N9-H(N7)hyp)2(p2 H20)2(S04)2(H20)2] [27], in which the... 

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