Dioxygen activation and catalysis around ambient temperature is a long-standing challenge in chemistry. Inspired by the significant roles of the hydrogen bond network in dioxygen activation and catalysis by redox enzymes, this work presents a Lewis acid improved dioxygen activation by an FeII(BPMEN)(OTf)2 complex towards tryptophan 2,3-dioxygenase (TDO) activity for 3-methylindole and common olefinic CC bond oxygenation and cleavage (enzymatic Brønsted acid vs. chemical Lewis acid). It was found that the presence of a Lewis acid such as Sc3+ could substantially improve olefinic CC bond oxygenation and cleavage activity through FeII(BPMEN)(OTf)2 catalyzed dioxygen activation. Notably, a more negative ρ value in the Hammett plot of para-substituted styrene oxygenations was observed in the presence of a stronger Lewis acid, disclosing the enhanced electrophilic oxygenation capability of the putative iron(III) superoxo species through its electrostatic interaction with a stronger Lewis acid. Thereof, this work has demonstrated a new strategy in catalyst design for dioxygen activation and catalysis for olefin oxygenation, a significant process in the chemical industry.
Convincing evidence revealed that some platinum-based drugs could stimulate immunological recognition, thereby inducing immunogenic cell death (ICD). Indoleamine-2,3-dioxygenase (IDO) is overexpressed in tumors, which caused exhaustion of tryptophan (T-cell energy) and constructed an immunosuppressive tumor microenvironment. Herein, considering IDO inhibition to improve chemotherapy, a series of IDOi-Pt(IV) prodrugs were designed to not only target DNA and IDO but also facilitate tumor-antigen exposure and immunomodulation. The optimal IDOi-Pt(IV) prodrugs (named compound 10) significantly enhanced intracellular accumulation 22.4-fold and cytotoxicity 61.75-fold superior to cisplatin in HeLa cells. Moreover, immunofluorescence and enzyme-linked immunosorbent assays revealed that 10 induced reactive oxygen species-mediated endoplasmic reticulum stress and secretion of damage-associated molecular patterns, thereby presenting ICD effects. Molecular docking, enzyme inhibition, and Western blot assays demonstrated that 10 could effectively inhibit IDO1 and reverse immunosuppression, as further verified by mixed leukocyte reactions. In vivo tests showed that 10 exhibited high-efficiency and low-toxicity antitumor effects compared to cisplatin, presenting successful chemoimmunotherapy.
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