Rehmannins A–D, Anti-inflammatory Carotenoid Pigments from the Fresh Root of <i>Rehmannia glutinosa</i>

Four novel carotenoid derivatives, rehmannins A-D (<b>1</b>-<b>4</b>), were isolated from the fresh roots of the traditional Chinese medicinal plant <i>Rehmannia glutinosa</i>. The structures of these new compounds were determined by extensive spectroscopic methods (high-resolution mass spectrometry, NMR, and electronic circular dichroism) and X-ray diffraction analysis. Rehmannins B-D (<b>2</b>-<b>4</b>) possess a novel tricyclic ring system bearing five contiguous stereocenters on the heterocyclic core together with a unique amide group on the long chain, rendering them attractive targets for total synthesis. Furthermore, plausible biosynthetic routes for these metabolites are suggested. Compound <b>3</b> exhibited the inhibition of NO secretion in LPS-induced RAW264.7 cells.