Anthraquinones and other constituents from the roots of Eremomastax speciosa (Hochst.) Cufod

Abstract

The chemical investigation of the roots of Eremomastax speciosa (Hochst.) Cufod (Acanthaceae). led to the isolation of thirteen compounds including five anthraquinones 1,8-dihydroxy-3-methylanthraquinone (1), 1,8-dihydroxy-3-methoxy-6-methylanthraquinone (2), emodin (3), aloe emodin (4) and 8-O-D-glucopyranosideemodin (5); one phenylethanoid glucoside acteoside (6); one benzophenone 2,6-dimethoxybenzophenone (7); two pentacyclic triterpenoids lupeol (8) and betulinic acid (9); three phytosterols stigmasterol (10), β-sitosterol (11), and β-sitosterol-3-O-β-D-glucopyranoside (12) and one fatty acid hexadecanoid acid (13). All these compounds are firstly reported from the roots of E. speciosa. Emodin and acteoside were modified chemically through allylation reaction to afford 3-O-allylated emodin (3a) and a new perallylated acteoside derivative (6a), respectively. The structure of the isolated compounds as well as those of the allylated derivatives were established by means of spectroscopic methods: NMR analysis (1H and 13C NMR, 1H–1H–COSY, HSQC and HMBC), high-resolution mass spectrometry (HR-ESI-MS) and by comparison with previously reported data. All those compounds were tested for their cytotoxic activity against the human cervix carcinoma KB-3-1 cells and their antioxidant activity, the allylated acteoside derivative and 2,6-dimethoxybenzophenone showed weak cytotoxicity while acteoside showed a good antioxidant activity. In addition, the chemotaxonomic significance of the isolated compound is discussed.