Discovery of new 13(17)-epoxymyrsinane diterpenes from aerial flowering parts of euphorbia spinidens Bornm. ex Prokh. with proapoptotic activities against human bladder cancer EJ138 cells

Phytochemical analysis of aerial flowering parts of Euphorbia spinidens Bornm. ex Prokh. from Euphorbiaceae family (local name: Farfion-e-dandaneh-khari) led to the isolation of five diterpenes based on myrsinane backbone. Using HRESI-MS, 1D, and 2D NMR, they were identified as two previously unreported: 33,7,14,15(β)-tetraacetyl-5(α)-butanoyl-13α(17)epoxy-8,10(18)-myrsinadiene (1), 7,14,15(β)-triacetyl-3(β),5(α)-dibutanoyl-13α(17)epoxy-8,10(18)-myrsinadiene (2), and three known diterpenes: 3,7,14,15(β)-tetraacetyl-5(α)-propanoyl-13(17)-epoxy-8,10(18)-myrsinadiene (3), and 3,7,10,14,15(β)-Pentaacetyl-5(α)-butanoyl-13,17-epoxy-8-myrsinene (4), 3,7,10,14,15(β)-pentaacetyl-5(α)-propanoyl-13,17-epoxy-8-myrsinene (5). Compound 5 was previously reported in the roots of the same plant but without NMR data. Therefore, its mass pattern,¹H-, and ¹³C-NMR data are reported. The cytotoxicity and proapoptotic properties of 1-3 were evaluated against EJ-138 bladder carcinoma cells through standard 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay for cytotoxicity screening and annexin V-FITC/PI apoptosis detection kit. In the cytotoxicity assay, the IC₅₀ values found against EJ-138 were: (1) 41.6 ± 3.54 μM; (2) 38.4 ± 2.54 μM; (3) 57.3 ± 5.4 μM, whilst the IC₅₀ value of doxorubicin was 1.7 ± 0.3 μM, respectively. In apoptosis assay, total apoptosis of compounds 1-3 at higher concentrations (100 μM) were 57.6 ± 3.54, 46.3 ± 2.82, and 57.2 ± 4.35%, respectively.