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An unprecedented 5,6-dihydroxyindole macrocycle (4) featuring a rigid twisted backbone was obtained by biomimetic oxidative cross-coupling of the 2,2'-biindole 2 and triindole 3. A putative reaction intermediate, 2-quinone, was detected and characterized by pulse radiolysis and DFT calculations. Discovery of 4 indirectly supports for the first time theoretically predicted cyclic structural motifs as potential eumelanin building blocks.
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Arzillo et al. (2010) studied this question.
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