title: 2-(Iodoethenyl)benzylamines as Potential Probes for Radical Intermediates Formed during Monoamine Oxidase Catalyzed Oxidations.
abstract: An attempt to trap radical intermediates during the monoamine oxidase (MAO) catalyzed oxidation of amines by intramolecular cyclization with an activated alkene that is built into the substrate was unsuccessful. (E)-2-(Iodoethenyl)benzylamine (3a) was shown to be a reversible inhibitor of MAO B, but the corresponding Z isomer (3b) was a good substrate. By GC-MS analysis, the expected radical trapping product, isoquinoline (5), was observed as one of two products in a 1:1 ratio. However, NMR analysis prior to GC-MS analysis showed no evidence of isoquinoline, suggesting that the isoquinoline was generated during gas chromatography. As a model for this GC-dependent reaction, the corresponding aldehyde, (Z)-2-(iodoethenyl)benzaldehyde (14), was treated with ammonia, and the product was analyzed by GC-MS; isoquinoline was detected. Likewise, the reaction of 14 with methylamine also produced isoquinoline by GC-MS analysis (but not by NMR analysis). These results are explained by electrocyclization of the corresponding imines at the elevated temperatures in the GC (Schemes 7 and 8). Substrate 3b and aldehyde 14 were recovered when the enzyme reaction products were chromatographed, although they were not detected by GC-MS. These products could arise via hydrolytic decomposition of the corresponding imine (17; Scheme 9). GC-MS analysis of 17 produced isoquinoline and (Z)-2-(iodoethenyl)benzyl iodide (18) in a 1:1 ratio; these are the two products observed in a 1:1 ratio after incubation of MAO with 3b and apparently arise from thermally induced electrocyclization and iodide ion cleavage (Scheme 9).
authors.affiliation: Department of Chemistry and Department of Biochemistry, Molecular Biology, and Cell Biology, Northwestern University, Evanston, Illinois 60208-3113.
authors.forename: Xueqing
authors.initials: X
authors.lastname: Wang
authors.forename: Richard B.
authors.initials: RB
authors.lastname: Silverman