An asymmetrical true-dimeric cadinane via ketonic bridge [C-15/C-3'], dysotican F (1), two symmetrical pseudo-cadinane dimers through an O-ether linkage [C-3/C-3'], dysoticans G (2) and H (3), as well as three known sesquiterpenoids 4-6 were obtained from the stem bark of Dysoxylum parasiticum (Osbeck) Kosterm. (Meliaceae). Their structures were determined by spectroscopic and quantum chemical calculations of 13C NMR shifts using a GIAO method and electronic circular dichroism (ECD) using a TDDFT method. A possible biogenetic pathway for 1-3 beginning from the known compounds (i-ii) was proposed. Cytotoxic evaluation showed that 2 as a new lead compound is the most potent against the MCF-7 and HeLa cell lines with IC50 values of 12.07 ± 0.17 μM and 9.29 ± 0.33 μM, while 1 has moderate inhibition with IC50 values of 31.59 ± 0.34 μM and 27.93 ± 0.25 μM. Furthermore, 3 is a selective inhibitor against the HeLa cell growth with an IC50 value of 39.72 ± 0.18 μM. A brief structure-activity relationship analysis of all isolated compounds 1-6 was also provided, including comparison with the coexisting molecules in the previous report.
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