N-Dealkylation of an N-Cyclopropylamine by Horseradish Peroxidase. Fate of the Cyclopropyl Group
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- 作者：Christopher L. Shaffer ; Martha D. Morton ; and Robert P. Hanzlik
- 刊名：Journal of the American Chemical Society
- 出版年：2001
- 出版时间：September 5, 2001
- 年：2001
- 卷：123
- 期：35
- 页码：8502 - 8508
- 全文大小：94K
- 年卷期：v.123,no.35(September 5, 2001)
- ISSN：1520-5126
文摘
Cyclopropylamines inactivate cytochrome P450 enzymes which catalyze their oxidative N-dealkylation. A key intermediate in both processes is postulated to be a highly reactive aminium cation radicalformed by single electron transfer (SET) oxidation of the nitrogen center, but direct evidence for this hasremained elusive. To address this deficiency and identify the fate of the cyclopropyl group lost uponN-dealkylation, we have investigated the oxidation of N-cyclopropyl-N-methylaniline (3) by horseradishperoxidase, a well-known SET enzyme. For comparison, similar studies were carried out in parallel withN-isopropyl-N-methylaniline (9) and N,N-dimethylaniline (8). Under standard peroxidatic conditions (HRP,H2O2, air), HRP oxidizes 8 completely to N-methylaniline (4) plus formaldehyde within 15-30 min, whereas9 is oxidized more slowly (<10% in 60 min) to produce only N-isopropylaniline (10) and formaldehyde (acetoneand 4 are not formed). In contrast to results with 9, oxidation of 3 is complete in <60 min and affords 4 (20%yield) plus traces of aniline. By using [1'-14C]-3, [1'-13C]-3, and [2',3'-13C]-3 as substrates, radiochemical andNMR analyses of incubation mixtures revealed that the complete oxidation of 3 by HRP yields 4 (0.2 mol),
le">-hydroxypropionic acid (17, 0.2 mol), and N-methylquinolinium (16, 0.8 mol). In buffer purged with pureO2, the complete oxidation of 3 yields 4 (0.7 mol), 17 (0.7 mol), and 16 (0.3 mol), while under anaerobicconditions, 16 is formed quantitatively from 3. These results indicate that the aminium ion formed by SEToxidation of 3 undergoes cyclopropyl ring fragmentation exclusively to generate a distonic cation radical (14+
ll.gif">)which then partitions between unimolecular cyclization (leading, after further oxidation, to 16) and bimolecularreaction with dissolved oxygen (leading to 4 and 17 in a 1:1 ratio). Neither le">-hydroxypropionaldehyde, acrolein,nor cyclopropanone hydrate are formed as SET metabolites of 3. The synthetic and analytical methods developedin the course of these studies should facilitate the application of cyclopropylamine-containing probes to reactionscatalyzed by cytochrome P450 enzymes.
le">-hydroxypropionic acid (17, 0.2 mol), and N-methylquinolinium (16, 0.8 mol). In buffer purged with pureO2, the complete oxidation of 3 yields 4 (0.7 mol), 17 (0.7 mol), and 16 (0.3 mol), while under anaerobicconditions, 16 is formed quantitatively from 3. These results indicate that the aminium ion formed by SEToxidation of 3 undergoes cyclopropyl ring fragmentation exclusively to generate a distonic cation radical (14+ll.gif">)which then partitions between unimolecular cyclization (leading, after further oxidation, to 16) and bimolecularreaction with dissolved oxygen (leading to 4 and 17 in a 1:1 ratio). Neither le">-hydroxypropionaldehyde, acrolein,nor cyclopropanone hydrate are formed as SET metabolites of 3. The synthetic and analytical methods developedin the course of these studies should facilitate the application of cyclopropylamine-containing probes to reactionscatalyzed by cytochrome P450 enzymes.