A new look at the rearrangement of adrenochrome under biomimetic conditions

At physiol. pH values, the rearrangement of adrenochrome leads, besides adrenolutin, to a major dimeric compd. consisting of an adrenolutin moiety covalently linked to the angular 9-position of adrenochrome. When the reaction is carried out in air, the initially generated adrenolutin undergoes autoxidn. to give 5,6-dihydroy-1-methylisatin (DHMIs), which smoothly oxidized to the 4,4'-dimer. Under an O2-depleted atm., formation of these latter compds. is prevented, and the rearrangement of adrenochrome leads mainly to the adrenochrome dimer (∼50% yield) along with adrenolutin and 5,6-dihydroxy-1-methylindole (DHMI) in ∼10% yield each. The product distribution is markedly dependent on the concn. of the aminochrome undergoing rearrangement, the nature of the buffer system used, and the pH of the medium. Heavy metal ions of common occurrence in biol. systems, such as Cu2+, Zn2+, or Co2+, significantly direct the reaction course toward the formation of adrenolutin, whereas Fe2+ and other cations with low redox potentials induce the almost exclusive formation of DHMI.