Uric acid (UA) is known to play an important role as an endogenous antioxidant. However, its insolubility in the serum is a risk for hyperuricemia. We assume that UA is an equivalent to hydroquinone or p-aminophenol, which can be oxidized to quinone/quinoimine and thus acts as a radical scavenger. Based on this hypothesis, a series of UA analogs was designed and synthesized. In the chemical radical scavenging assay, active compounds were considered as hydroquinone or p-aminophenol equivalents. A highly functionalized UA structure is not essential to have radical scavenging activity. Potent active 5-hydroxyindolinones (1a, 2a, and 3a) showed sufficient activity with high solubility and low cytotoxicity.
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