Tri‐ and Bicyclic Taxoids from the Taiwanese Yew Taxus sumatrana

Five new taxoids, including a new 2(3→20)‐ abeo ‐taxane with a 6/10/6‐membered ring system and four 3,8‐ seco ‐taxanes having a 6/12‐membered ring system, were isolated from an acetone extract of the leaves and twigs of the Taiwanese yew ( Taxus sumatrana , Taxaceae). The structures were established as 2 α ,7 β ,10 α ‐triacetoxy‐5 α ‐hydroxy‐2(3→20)‐ abeo ‐taxa‐4(20),11‐dien‐9,13‐dione ( 1 ), (3 E ,8 E )‐2 α ,9,10 β , 13 α ,20‐pentaacetoxy‐7 β ‐hydroxy‐3,8‐secotaxa‐3,8,11‐trien‐5‐one ( 2 ), (3 E ,8 E )‐2 α ,9,10 β ,13 α ,20‐pentaacetoxy‐5 α ,7 β ‐dihydroxy‐3,8‐secotaxa‐3,8,11‐triene ( 3 ), (3 E ,8 E )‐9,10 β ,13 α ‐triacetoxy‐2 α ,7 β ,20‐trihydroxy‐5 α ‐[(2 E )‐cinnamoyloxy]‐3,8‐secotaxa‐3,8,11‐triene ( 4 ), and (3 E ,8 E )‐2 α ,5 α ,7 β ,9,10 β ,13 α ‐hexaacetoxy‐20‐hydroxy‐3,8‐secotaxa‐3,8,11‐triene ( 5 ), respectively, on the basis 1D‐ and 2D‐NMR spectral analyses. The in vitro cytotoxic activity of compounds 1 – 5 against four human tumor cell lines, including HeLa (cervical epitheloid), WiDr (colon), Daoy (medulloblastoma), and Hep2 (liver carcinoma) tumor cells was evaluated. Whereas compounds 1 – 3 were inactive, the novel taxanes 4 and 5 showed significant cytotoxicity.