Identification of New Compounds from the Roots of Rubia tibetica Hook. f.

Rubia tibetica Hook. f is a traditional Tibetan medicinal plant, with its roots serving as the primary medicinal part. Two new compounds, Rubiaxylm C and E (1 and 3), and one new natural compound, Rubiaxylm D (2) were isolated from R. tibetica, along with five known compounds (4-8). The structures of the previously undescribed compounds were elucidated by HR-ESIMS, 1D/2D NMR spectroscopic data and electronic circular dichroism calculations. Compound 1 is a rare anthrone substituted with a carbonyl group at position 1. Furthermore, all isolated compounds were tested for their cytotoxicity against HepG2 cell lines.