2.3- Dihydro-5,6-dihydroxyindoles

AC5047), and the formation of 2,3-dihydro-5,6-dihydroxyindoles in this way was reviewed in 2005 (05AHC(89)1). 

The most significant 2,3-dihydro-5,6-dihydroxyindole is L-cyclodopa 78, also known as leucodopachrome, which is an intermediate in the biosynthesis of eumelanin and is formed by the spontaneous cyclization of dopaquinone 79 (92MI2) (04MI1). In turn, cyclodopa is readily oxidized to dopachrome 80 but this oxidation can be reversed chemically using sodium dithionite. Wyler and Chiovini have described the preparation of both enantiomers of cyclodopa using transformations... 

Oxidative polymerization of phenol derivatives is also important pathway in vivo, and one example is the formation of melanin from tyrosine catalyzed by the Cu enzyme, tyrosinase. The pathway from tyrosine to melanin is described by Raper (7) and Mason (8) as Scheme 8 the oxygenation of tyrosine to 4-(3,4-dihydro-xyphenyl)-L-alanin (dopa), its subsequent oxidation to dopaqui-none, its oxidative cyclization to dopachrome and succeeding decarboxylation to 5,6-dihydroxyindole, and the oxidative coupling of the products leads to the melanin polymer. The oxidation of dopa to melanin was attempted here by using Cu as the catalyst. 

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