Melanin and its precursors. 8. The oxidation of methylated 5:6-dihydroxyindoles

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Abstract
The 2-, 5- and 6-methyl derivatives of 3,4-dihydroxyphenylalanine were subjected to aerial oxidation: only the first two yield melanins. Only the last-is a substrate for tyrosinase. A stable red solution prepared by oxidation of 5,6-dihydroxy-2,3-dimethylindole with silver oxide in methanol is considered to contain the corresponding o-quinone. The oxidation by molecular O2 of 5,6-dihydroxyindole and of seven of its derivatives containing methyl groups in various positions has been studied under carefully controlled conditions. The results obtained support the general pattern of melanogenesis proposed by Bu''Lock, and Harley-Mason (1951). Other current theories are also discussed.