Characterization and antimicrobial evaluation of anthraquinones and triterpenes from Rubia cordifolia

Chemical investigation of roots of the plant, Rubia cordifolia Linn, led to the isolation of an undescribed anthraquinone, cordifoquinone R, determined as 1,2-dihydroxy-6-methoxyanthracene-9,10-dione (6) based on the 1D and 2D NMR analyses and HRESIMS. Ten other known compounds viz.1,4-dihydroxy-2-methoxyanthracene-9,10-dione (1), rubiadin (2), xanthopurpurin (3), 1-methoxy-3-hydroxy-2-carbomethoxy-9,10-anthraquinone (4), alizarin (5), β-sitosterol glucoside (7), scopoletin (8), oleanolic acid, (9), pomolic acid (10), queretaroic acid (11) were also isolated. Out of these compounds, 4, 10, and 11 are first reported from this plant species. Compounds 2, 3, 6, 7, and 10 showed activity in the range of 16-32 µg/ml against S. aureus ATCC 29213.