The Melanin Problem : a Synthesis of 5 : 6-Dihydroxyindole

Abstract

WE have recently submitted to the Chemical Society a paper describing, inter alia, a new synthesis of 5-hydroxyindole by reduction with iron powder and acetic acid of 2 : β -dinitro-5-acetoxystyrene and deacetylation of the resulting 5-acetoxyindole. As a part of a comprehensive investigation of the chemistry of the natural melanins, we have now successfully extended the method to the synthesis of 5 : 6-diacetoxyindole (compact hemispherical clusters, m.p. 135–136° ; found : C, 61·5 ; H, 4·9 ; N, 6·3 : C₁₂H₁₁O₄N requires C, 61·8 ; H, 4·7 ; N, 6·0 per cent), and of 5 : 6-dihydroxyindole (colourless needles, m.p. 140° ; found: C, 64·7 ; H, 4·85 ; N, 9·4 : C₈H₇O₂N requires C, 64·4 ; H, 4·7 ; N, 9·4 per cent). The latter compound was postulated by Raper¹ as an unstable intermediate in the enzyme-catalysed oxidation of tyrosine to melanin, and has been known hitherto only in solution or in the form of its derivatives.