Indirubin, long known for its potential as a kinase inhibitor, also exhibits promise as a novel anion-binding agent with selectivity for oxyanions such as phosphate. Initial evaluation of 7,7’-diazaindirubin elicited a color shift from red to blue/purple when introduced to tetrabutylammonium dihydrogen phosphate in DMSO with a binding constant if 290 M<sup>-1 </sup>consistent with 1:1 binding. This effect was qualitatively observed in other indirubins with stronger responses observed for more electron deficient systems. To ultimately design functional systems able to bind phosphate and phosphorylated compounds, a systematic evaluation was undertaken using nitroindirubins as the synthetic platform. These compounds were synthesized using a recently developed synthetic method using Mo(CO)<sub>6 </sub>and cumyl peroxide to generate an indoxyl intermediate. This intermediate led to the synthesis of homodimeric dinitroindirubins and, in the presence of isatin as a trapping agent, heterodimeric nitroindirubins.

Evaluating the anion-binding potential of electron deficient indirubins

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ACS Fall 2022

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