<jats:sec><jats:title>Background and Purpose</jats:title><jats:p>The transcription factor <jats:styled-content style="fixed-case">NF</jats:styled-content>‐<jats:styled-content style="fixed-case">κB</jats:styled-content> orchestrates many pro‐inflammatory signals and its inhibition is considered a promising strategy to combat inflammation. Here we report the characterization of the natural product plumericin as a highly potent inhibitor of the <jats:styled-content style="fixed-case">NF</jats:styled-content>‐<jats:styled-content style="fixed-case">κB</jats:styled-content> pathway with a novel chemical scaffold, which was isolated via a bioactivity‐guided approach, from extracts of <jats:italic><jats:styled-content style="fixed-case">H</jats:styled-content>imatanthus sucuuba</jats:italic>, an <jats:styled-content style="fixed-case">A</jats:styled-content>mazonian plant traditionally used to treat inflammation‐related disorders.</jats:sec><jats:sec><jats:title>Experimental Approach</jats:title><jats:p>A <jats:styled-content style="fixed-case">NF</jats:styled-content>‐<jats:styled-content style="fixed-case">κB</jats:styled-content> luciferase reporter gene assay was used to identify <jats:styled-content style="fixed-case">NF</jats:styled-content>‐<jats:styled-content style="fixed-case">κB</jats:styled-content> pathway inhibitors from <jats:italic><jats:styled-content style="fixed-case">H</jats:styled-content>. sucuuba</jats:italic> extracts. Monitoring of <jats:styled-content style="fixed-case">TNF</jats:styled-content>‐α‐induced expression of the adhesion molecules <jats:styled-content style="fixed-case">VCAM</jats:styled-content>‐1, <jats:styled-content style="fixed-case">ICAM</jats:styled-content>‐1 and <jats:styled-content style="fixed-case">E</jats:styled-content>‐selectin by flow cytometry was used to confirm <jats:styled-content style="fixed-case">NF</jats:styled-content>‐<jats:styled-content style="fixed-case">κB</jats:styled-content> inhibition in endothelial cells, and thioglycollate‐induced peritonitis in mice to confirm effects <jats:italic>in vivo</jats:italic>. Western blotting and transfection experiments were used to investigate the mechanism of action of plumericin.</jats:sec><jats:sec><jats:title>Key Results</jats:title><jats:p>Plumericin inhibited <jats:styled-content style="fixed-case">NF</jats:styled-content>‐<jats:styled-content style="fixed-case">κB</jats:styled-content>‐mediated transactivation of a luciferase reporter gene (<jats:styled-content style="fixed-case">IC<jats:sub>50</jats:sub></jats:styled-content> 1 μM), abolished <jats:styled-content style="fixed-case">TNF</jats:styled-content>‐α‐induced expression of the adhesion molecules <jats:styled-content style="fixed-case">VCAM</jats:styled-content>‐1, <jats:styled-content style="fixed-case">ICAM</jats:styled-content>‐1 and <jats:styled-content style="fixed-case">E</jats:styled-content>‐selectin in endothelial cells and suppressed thioglycollate‐induced peritonitis in mice. Plumericin exerted its <jats:styled-content style="fixed-case">NF</jats:styled-content>‐<jats:styled-content style="fixed-case">κB</jats:styled-content> pathway inhibitory effect by blocking <jats:styled-content style="fixed-case">IκB</jats:styled-content> phosphorylation and degradation. Plumericin also inhibited <jats:styled-content style="fixed-case">NF</jats:styled-content>‐<jats:styled-content style="fixed-case">κB</jats:styled-content> activation induced by transfection with the constitutively active catalytic subunit of the <jats:styled-content style="fixed-case">IκB</jats:styled-content> kinase (<jats:styled-content style="fixed-case">IKK</jats:styled-content>‐β), suggesting <jats:styled-content style="fixed-case">IKK</jats:styled-content> involvement in the inhibitory action of this natural product.</jats:sec><jats:sec><jats:title>Conclusion and Implications</jats:title><jats:p>Plumericin is a potent inhibitor of <jats:styled-content style="fixed-case">NF</jats:styled-content>‐<jats:styled-content style="fixed-case">κB</jats:styled-content> pathways with a new chemical scaffold. It could be further explored as a novel anti‐inflammatory lead compound.</jats:sec>