Rare cytochalasans isolated from the mangrove endophytic fungus Xylaria arbuscula.

Four new cytochalasans, arbuschalasins A-D (1-4), along with thirteen known analogues (5-17), were isolated from the solid rice medium of endophytic fungus Xylaria arbuscula. Arbuschalasins A-B feature a rare 5/6/6/6 fused ring system while arbuschalasin D was characterized as the first example of natural cytochalasans that possesses a 5/5/11 fused scaffold. The structures of 1-4 were assigned by spectroscopic data, with their absolute structures being determined by electronic circular dichroism (ECD) calculations. All of the isolates were evaluated against the human colorectal adenocarcinoma cell lines (HCT15). Compounds 6 and 7 showed significant inhibitory effects (IC50 values were 13.5 and 13.4 µM, respectively), being more active than those of the positive control, fluorouracil (103.1 µM).

Quassinoids from the Roots of Eurycoma longifolia and Their Anti-Proliferation Activities.

A phytochemical investigation on the roots of medicinal plant Eurycoma longifolia resulted in the isolation of 10 new highly oxygenated C20 quassinoids longifolactones G‒P (1-10), along with four known ones (11-14). Their chemical structures and absolute configurations were unambiguously elucidated on the basis of comprehensive spectroscopic analysis and X-ray crystallographic data. Notably, compound 1 is a rare pentacyclic C20 quassinoid featuring a densely functionalized 2,5-dioxatricyclo[5.2.2.04,8]undecane core. Compound 4 represents the first example of quassinoids containing a 14,15-epoxy functionality, and 7 features an unusual α-oriented hydroxyl group at C-14. All isolated compounds were evaluated for their anti-proliferation activities on human leukemia cells. Among the isolates, compounds 5, 12, 13, and 14 potently inhibited the in vitro proliferation of K562 and HL-60 cells with IC50 values ranging from 2.90 to 8.20 µM.

Unprecedented Quassinoids from Eurycoma longifolia: Biogenetic Evidence and Antifeedant Effects.

Six new quassinoids (1-6) were isolated from the roots of Eurycoma longifolia, and their structures with absolute configurations were determined unambiguously by spectroscopic analyses and single-crystal X-ray crystallographic experiments. Compounds 1 and 2 are the first members of a new class of quassinoids with an unusual C26 carbon skeleton. Compound 6 features a C20 cage-like scaffold with an unprecedented densely functionalized 2,5-dioxatricyclo[5.2.2.04,8]undecane core. The discovery of the two C26 quassinoids 1 and 2 has provided firm evidence for the better understanding the biogenetic process from C30 triterpenoid precursors to quassinoids. Compound 5 exhibited significant antifeedant activity on the diamondback moth (DBM) larvae and excellent systemic absorption and accumulated properties in Brassica chinensis.