Melanins are some of the least understood biopolymers, but they have the potential to have a significant positive impact in non-biological applications, including as water purification tools and organic semiconductors. Among the three kinds of melanins found in humans, our lab has focused on studying the properties of eumelanin, the form of melanin that gives rise to black and brown coloration in hair and skin. Eumelanin is thought to be composed of oligomers of 5,6-dihydroxyindoles. In this project, we are investigating commercially available 5,6-dimethoxyindole (DMI) as a starting material for the construction of synthetic eumelanin analogs. We have investigated the iridium-catalyzed borylation of DMI and tosyl-protected DMI, and have explored conditions for Suzuki coupling reactions of the resulting borylated indoles. During attempted Suzuki reactions, we have observed and isolated a blue product that is likely 5,5’,6,6’-tetramethoxyindigo (TMI), a known derivative of the venerable dye, indigo. Previous synthetic routes afford TMI in low yield, and we are currently exploring this serendipitous finding to develop a new synthetic route to TMI. This poster describes our recent studies of modified Suzuki-Miyaura coupling reactions with borylated DMI, toward the goal of constructing eumelanin and indigo analogs.

Synthesis of dimethoxyindole-based eumelanin and indigo analogs

249th National Meeting (2015)

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