Pauciflorins A-E, Unexpected Chromone-Monoterpene-Derived Meroterpenoids from Centrapalus pauciflorus .

Five unusual meroterpenoids based on new carbon skeletons, pauciflorins A-E ( 1 - 5 ), were isolated by multistep chromatographic separations of a methanol extract of the aerial parts of Centrapalus pauciflorus . Compounds 1 - 3 are derived by the connection of a 2-nor-chromone and a monoterpene unit, whereas 4 and 5 are dihydrochromone-monoterpene adducts with a rarely occurring orthoester functionality. The structures were solved using 1D and 2D NMR, HRESIMS, and single-crystal X-ray diffraction. Pauciflorins A-E were evaluated for antiproliferative activity against human gynecological cancer cell lines, but were inactive (IC 50 < 10 μM) in each case.