28-Norlupanes and dammaranes from the heartwood of Dipterocarpus costatus Gaertn. f. (Dipterocarpaceae) and their cytotoxic and antiplasmodial activities

Triterpenoids of natural origin are of increasing interest due to their broad spectrum of biological activities. Previous studies on dipterocarpaceous plants have reported that they were valuable source of new active natural compounds. As part of an ongoing search for naturally occurring bioactive triterpenoids from Dipterocarpaceae, phytochemical investigation of Dipterocarpus costatus Gaertn. f. heartwood collected in Thailand was conducted. Seventeen triterpenoids (1-17) belonging to both 28-norlupane and dammarane series were isolated from the corresponding bioactive n-hexane extract. Among them, norlupane 1 was identified as previously undescribed and norlupane 2 was described for the first time from a natural source. Compound structures were elucidated by 1D/2D-NMR spectroscopy and mass (HRMS) spectrometry. All isolated molecules were tested for their cytotoxicity on two human colorectal carcinoma cell lines (i.e. HT-29 and HCT116), as well as for their antiplasmodial activity against chloroquine-resistant strain FcB1 of Plasmodium falciparum. Norlupanes 2 and 4 were shown to exhibit a good cytotoxic activity against HCT 116 (IC₅₀=4.2 µM) and potent antiplasmodial activity (IC₅₀=3.74 µM), respectively.