Two novel naphthohydroquinone dimers with unprecedented skeletons, rubialatins A (1) and B (2), were isolated from the herbal plant Rubia alata together with their precursor, mollugin (3). The structures were elucidated on the basis of NMR spectra and crystal X-ray diffraction. Compound 1, a racemate, was separated by chiral column chromatography, and the absolute configurations of the enantiomers were determined by the computational methods. Cytotoxicity of 1-3 was evaluated as well as the effect on the NF-?B pathway. Compound (+)-1 showed cytotoxicity and could inhibit NF-kappa B pathway. Meanwhile, 2 showed cytotoxicity and a synergistic effect with TNF-alpha on NF-omicron B activation.
National Key Basic Research Program of China [2014CB954100]
; Key Research Program of the Chinese Academy of Sciences [KJZD-EW-L07]
; National Natural Science Foundation of China 
; Science and Technology Program of Yunnan Province [2008GA029]