(+)/(-)-Gerbeloid A, a pair of unprecedented coumarin-based polycyclic meroterpenoid enantiomers from Gerbera piloselloides: Structural elucidation, semi-synthesis, and lipid-lowering activity

A pair of coumarin-based polycyclic meroterpenoid enantiomers (+)/(-)-gerbeloid A [(+)-1a and (-)-1b] were isolated from the medicinal plant Gerbera piloselloides, which have a unique caged oxatricyclo [4.2.2.0^3,8] decene scaffold. Their planar and three-dimensional structures were exhaustively characterized by comprehensive spectroscopic data and X-ray diffraction analysis. Guided by the hypothetical biosynthetic pathway, the biomimetic synthesis of racemic 1 was achieved using 4-hydroxy-5-methylcoumarin and citral as the starting material via oxa-6π electrocyclization and intramolecular [2 + 2] photocycloaddition. Subsequently, the results of the biological activity assay demonstrated that both (+)-1a and (-)-1b exhibited potent lipid-lowering effects in 3T3-L1 adipocytes and the high-fat diet zebrafish model. Notably, the lipid-lowering activity of (+)-1a is better than that of (-)-1b at the same concentration, and molecular mechanism study has shown that (+)-1a and (-)-1b impairs adipocyte differentiation and stimulate lipolysis by regulating C/EBPα/PPARγ signaling and Perilipin signaling in vitro and in vivo. Our findings provide a promising drug model molecule for the treatment of obesity.