Two New Limonoids from the Root Bark of Chinese Medicinal Plant Dictamnus dasycarpus

Two new limonoids, kihadanin C (1) and 23-methoxydasylactone A (2), together with seven related known ones, 3-9, were isolated from the root bark of the plant Dictamnus dasycarpus. The structures of the new compounds were elucidated on the basis of extensive analyses of their spectroscopic data (1D- and 2D-NMR, MS) and by comparison of their NMR data with those reported in the literature. To the best of our knowledge, 1 presents the first example of A, D-seco limonoid with an unusual 3,4-dihydroxy-2,5-dimethoxytetrahydrofuran moiety as ring E. In the bioassay in vitro, 7 showed moderate antibacterial activity against Staphylococcus aureus, while 8 and 9 displayed neuroprotective activities against H2O2-induced injury in SH-SY5Y cells.