Cytotoxic indole diterpenoids from the fungus Aspergillus pseudonomius: isolation, structural elucidation, and biological evaluation.

Two new indole diterpenoids, 21,22-dideprenyl-20-(3-methylbut-1-enyl) shearinine (1) and 14S-hydroxy-β-aflatrem (2) together with eight known compounds (3-10) were isolated from the Aspergillus pseudonomius. Among them, compound 1 featured a highly unusual 6/8/6/6/6 pentacyclic ring system incorporating a rare eight-membered lactam ring. Compound 2 represented a hydroxylated classical 6/5/5/6/6/6 indole diterpenoid scaffolds. The structures of compounds 1 and 2 were determined by NMR data, HRESIMS, and electronic circular dichroism (ECD) calculations. The plausible biosynthetic pathways of compounds 1 and 2 were proposed. Furthermore, compound 1 exhibited promising activity against A549 cells with an IC50 value of 8.67 ± 1.67 μM, while compound 2 showed notable inhibitory activity toward HCT-8 cells with an IC50 value of 8.48 ± 0.92 μM. Mechanistically, compound 1 induced G0/G1 phase arrest, whereas compound 2 caused G2/M phase arrest. Both compounds triggered mitochondria-mediated apoptosis via BAX/Bcl-2 modulation and mitochondrial membrane potential (ΔΨm) disruption. Collectively, these findings expand the structural diversity of indole diterpenoids and highlight their potential as promising leads for anticancer drug discovery.