Triterpenoidal and Phenolic Compounds Isolated from the Aerial Parts of Helicteres hirsuta and their Cytotoxicity on Several Cancer Cell Lines

Helicteres L. is one of the genera of the Sterculiaceae family with several remarkable activities. Previous studies revealed that terpenoids, flavonoids, and lignans are the dominant constituents of Helicteres species. However, information about this genus is scarce and unsystematic. Most of the phytochemical and pharmacological investigations have been mainly reported on Helicteres angustifolia and Helicteres isora, which are commonly used in China and Indonesia, respectively. In the present study, two terpenoids: 3β- O-acetylbetulinic acid (1) and simiarenol (2) together with three phenolic compounds: 4,4'-sulfinylbis(2-( tert-butyl)-5-methylphenol) (3), 7- O-methylisoscutellarein (4), 7,4'-di- O-methylisoscutellarein (5), and a mixture of stigmasterol and β-sitosterol were isolated and structurally elucidated from the aerial parts of Helicteres hirsuta Lour. Compounds 1-5 were tested for cytotoxicity on four human cancer cell lines: leukemia CCRF-CEM, breast MDA-MB-231, colon HCT116 and glioblastoma U251 cancer cells. Among them, compounds 1 and 3 showed moderate activity on CCRF-CEM and HCT116 cancer cells with IC 50 values ranging from 14.6 to 31.5 μM (P < 0.05). This is the first time these compounds have been reported from this plant. To the best of our knowledge, compound 3 is novel in nature although it has been chemically synthesized before, and compounds 1, 2, and 4 are new to this plant family (Sterculiaceae).