Four new carbazole alkaloids, claurailas A-D (1-4), as well as 12 known carbazoles and three known coumarins were isolated from the roots of Clausena harmandiana. Heptaphylline (6) and 7-methoxyheptaphylline (7) showed strong cytotoxicity against NCI-H187 and KB cell lines with IC(50) values ranging from 1.3 to 2.7 μM. Compound 7 showed no cytotoxicity against Vero cells.

The activity guided fractionation of the Clausena harmandiana root extracts led to the isolation of a coumarin, a ferulate, and eight carbazoles. This is the first report of the isolation of compounds 2-4 and 6-10 from this species, and this is the first time 10 was isolated from this genus. Compound 4 showed strong cytotoxicity against NCI-H187 cells with an IC(50) value of 1.63 microg/mL. Compound 5 demonstrated strong cytotoxicity against MCF-7 and KB cell lines with IC50 values of 2.21 and 1.74 microg/mL, respectively. Compounds 3 and 4 exhibited moderate cytotoxicity against the MCF-7 cell line, and 8 showed moderate cytotoxicity against NCIH187 and KB cell lines. Compounds 3 and 5 showed antiplasmodial activity with IC(50) values of 3.27 and 2.94 microg/mL, respectively.

Nine carbazoles and three coumarins were isolated from C. harmandiana. Crude extracts and all isolates were evaluated for antioxidant activity using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and lipid peroxidation assay and cytotoxicity against cholangiocarcinoma, KKU-OCA17 and KKU-214 cell lines. 7-Hydroxyheptaphylline and nordentatin showed strong antioxidant activity on lipid peroxidation with IC50 values of 2.95 and 2.90 µM respectively, while the activity on a DPPH assay showed IC50 values of 56.82 and 29.3 µM, respectively. The two compounds exhibited strong cytotoxicity against KKU-OCA17 (IC50=88.7 and 46.1 µM, respectively) and KKU-214 (IC50=43.7 and 39.1 µM, respectively) cell lines. The results show convincingly that these compounds may be the promising leads for the development of cytotoxic agents.

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