Cytoprotective dihydronaphthalenones from the wood of Catalpa ovata

Three previously undescribed dihydronaphthalenones, 7-hydroxycatalponol, (4S)-3,4-dihydro-4-hydroxy-2-[(2R)-2,3-dihydroxy-3-methylbutylidene]naphthalen-1(2H)-one, and (6S)-5,6-dihydro-6-hydroxy-2,2-dimethyl-2H-benzo[h]chromen-4(3H)-one and one phthalide, (±)-3-(5-hydroxy-5-methyl-2-oxohex-3-en-1-yl)isobenzofuran-1(3H)-one, were isolated from the wood of Catalpa ovata G. Don (Bignoniaceae), together with six known compounds. The structures of the previously undescribed compounds were elucidated by interpretation of 1D and 2D NMR data. The absolute configurations of the dihydronaphthalenones were deduced by analysis of the ECD data and application of Mosher ester methodology. All isolates were investigated for their cytoprotective effects against hydrogen peroxide (H₂O₂)-induced oxidative damage in HepG2 cells. Moreover, the mRNA expression levels of antioxidant enzymes such as heme oxygenase-1 (HO-1) and NAD(P)H:quinine oxidoreductase 1 (NQO1) in HepG2 cells were examined by RT-PCR analysis. As a result, catalponol and epi-catalponol showed antioxidant activities via directly scavenging of intracellular ROS and inducing the antioxidant enzymes in vitro.