Conformational Analysis of 9-Substituted Adenines in Relation to Their Microsomal N1-Oxidation

Abstract

Metabolic N-oxidation of adenine, 9-methyladenine, 9-benzyladenine, 9-benzhydryladenine and 9-trityladenine has been investigated using hepatic microsomes from hamster, guinea-pig, rabbit, mouse, rat, and dog. N1-Oxide formation occurs with 9-benzyladenine and 9-benzhydryladenine using liver preparations of all species examined, although to different extents. The N-oxidase activity was found, amongst rodents, in the order hamster greater than mouse greater than rabbit greater than rat greater than guinea-pig. Microsomal preparations from dog liver contained a small quantity of P-450 and yet produced a relatively large amount of the N-oxides, possibly indicating that other cytochromes in addition to P-450 may be involved in the N-oxidation of these compounds. The most favourable conformations of these 9-substituted analogues have been established using computer graphics modelling and 1H NMR techniques. Results obtained confirmed the importance of the stereochemical properties of these compounds in relation to N1-oxidation. These observations substantiate and extend our previous findings on the electronic, lipophilic, and stereochemical factors affecting the N-oxidation of adenine derivatives.

N‐Oxidative Transformations ofCNGroups as Means of Toxification and Detoxification

“…Reverse-phase HPLC has been used for the separation of aldoximes 45 , ketoximes 46 , amidoximes 14,47 52 and nitrones 3,26,53 55 . This method also served to identify Noxides derived from pyridines 7,29,31,56 63 , pyrimidines 8,9,16 , pyrazines 9 , pyridazines 9 and purines 64,65 ; the latter class of heteroaromatic N-oxides was analyzed on cationic exchange columns.…”

“…In experiments with various 9-substituted adenines, the 1-N-oxide (43) derived from 9-benzyladenine has been found to be the major metabolite in dog liver microsomes, while 9-benzhydryladenine underwent N-oxygenation at the 1-position to considerably lower extent 65 . Studies with the two purines conducted with hepatic preparations from other species revealed increasing rates of 1-N-oxide formation in the order guinea-pig < rat < rabbit < mouse < hamster 64,65 .…”

Mutagenicity Testing of 9-N-Substituted Adenines and Their N-Oxidation Products

“…Previous studies on the metabolism -of 9-substitutedadenines showed that they were only coverted to 1-Noxides by a phenobarbital-inducible cytochrome P450 species, presumably CYP2B. This enzyme failed to oxidize adenine to adenine-1-N-oxide (11,12,24). Using rats pretreated with either 3-methylcholanthrene or isosafrole (inducers of CYP1), Clement and Kunze (25) demonstrated that adenine, at high substrate concentrations, was converted to 6-hydroxylaminopurine.…”

“…9-Benzhydryladenine (BHA), 9-benzhydryladenine-1-N-oxide (BHANO), 9-trityladenine (TA), and 9-trityladenine-1-Noxide (TANO) were prepared according to previously reported methods (12).…”

“…The metabolism of many of these compounds has been studied (1-3), and generally it has been observed that compounds used in clinical medicine are not genotoxic and are metabolized by oxidation at one or more nuclear nitrogens (6)(7)(8)(9)(10)(11)(12), whereas those produced by pyrolysis are potent mutagens (13) and are metabolized by N-hydroxylation of the exo amino group (14)(15)(16). This has led to the concept (1-3) that nuclear N-oxidation of aminoazaheterocycles is a detoxication process, whereas N-hydroxylation of the exo amino group is a toxication reaction (Fig.…”