Polycyclic Limonoids as Potential Nrf2 Inducers from <i>Trichilia connaroides</i>

An investigation of <i>Trichilia connaroides</i> uncovered connarolides A-D (<b>1</b>-<b>4</b>, respectively), four limonoids with exceptional multiring systems. Compound <b>1</b> showcased a unique 5/8/6/6-fused ring system distinguished by a bicyclo[5.2.1^2,4]decane A/B ring framework. Compound <b>2</b> featured a 5/8/6/5/6 scaffold incorporating a triply fused furan ring, and a long-conjugated system resulted from 3-deoxygenation. X-ray crystallography established the rare 6/3/6/6/6 ring system of <b>3</b>. Moreover, <b>4</b> was identified as an antioxidant, conferring cytoprotective activity through Nrf2 activation.