Ent-abietane diterpenoids from Suregada zanzibariensis Baill. (Euphorbiaceae), their cytotoxic and anticancer properties

The stem bark extract of Suregada zanzibariensis afforded a previously undescribed ent-abietane diterpenoid trivially named mangiolide (1) and a known jolkinolide B (2) via anticancer bioassay-guided fractionation. The CH₂Cl₂:MeOH extract of S. zanzibariensis was initially analysed for its anticancer properties against three cancer cell lines, renal (TK10), melanoma (UACC62), and breast (MCF7) and was found to be potent at low μg/mL ranges. Compound 1, 6α-acetoxy-14-keto-ent-abieta-7(8),13(15)-diene-16,12-olide (mangiolide) inhibited the growth of renal (TK10) with a GI₅₀ of 0.02 μg/mL; a GI₅₀ of 0.03 μg/mL for melanoma (UACC62) and a GI₅₀ of 0.05 μg/mL for breast (MCF7) cancer cell lines. Compound 2, 8,13-diepoxy-13,15-ent-abietene-16,12-olide (jolkinolide B) inhibited the growth (GI₅₀) of the cell lines at 3.31 μg/mL for renal (TK10), 0.94 μg/mL for melanoma (UACC62) and 2.99 μg/mL for the breast (MCF7). The structures were established on the basis of their spectroscopic analysis and the absolute stereostructures assigned using electronic circular dichroism (ECD).