SYNTHESIS, PHYSICOCHEMICAL PROPERTIES, AND AMINE OXIDATION REACTION OF INDOLEQUINONE DERIVATIVES AS MODEL COMPOUNDS OF NOVEL ORGANIC COFACTOR TTQ OF AMINE DEHYDROGENASES

3,4-Disubstituted 6,7-indolequinones -dimethyl-4-(3'-methylindol-2'-yl )indole-6,7-dione (2), 3-methyl-4-phenylindole-6,7-dione (3), and 3,4- dimethyl-6,7-dione (4)] and a 3,7-disubstituted 4,5-indolequinone [3,7 -dimethylindole-4,5-dione (5)] have been synthesized as models for the novel organic cofactor TTQ of bacterial amine dehydrogenases. The sub stituent and structural effects on the physicochemical properties of t he quinones have been investigated in detail by comparing the spectros copic data (UV-vis, IR, H-1- and C-13-NMR), pK(a) values of the pyrrol e proton, and the two-electron redox potentials with those of model co mpound 1 3-methyl-4-(3'-methylindol-2'-yl)indole-6,7-dione] previously reported (ref 5). Reactivity of each quinone in the transamination pr ocess [iminoquinone formation (k(1)), rearrangement to product-imine ( k(2)), and aminophenol formation (k(3))] has been investigated kinetic ally, revealing that the substituent and structural effects on the ami ne-oxidation reaction are not so significant. In the aerobic catalytic oxidation of benzylamine, however, the aromatic substituents on the q uinone ring play an important role to protect the quinone from the dea ctivation process of a Michael-type addition by the amine, making it a ct as an efficient turnover catalyst.