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Sphenostylisins A-K, NF-κB Inhibitors, Quinone Reductase Inducers, and Antioxidants from Sphenostylis marginata ssp. erecta
In a search for naturally occurring compounds that combat cancer, the chloroform-soluble extract of the root bark of S. marginata E. Mey. ssp. erecta (Baker f.) Verdc. (Fabaceae) collected in Zimbabwe showed hydroxyl radical-scavenging and quinone reductase-inducing activities, and thus was fractionated through bioactivity-guided isolation. Sphenostylisins A-C (1 – 3), three complex dimeric compounds representing two novel carbon skeletons, along with an additional eight new compounds, sphenostylisins D-K (4 – 11), were isolated from the active extract. Among them, nine compounds (1 – 5 and 8 – 11) showed hydroxyl radical-scavenging activity, six compounds (1 – 4, 8, and 9) showed quinone reductase-inducing activity, and eight compounds (1 – 8) showed NF-κB inhibitory activity, with sphenostylisin A (1, IC50= 6 nM) being a very potent NF-κB p65 inhibitor.