Aspertaichamide B, a new anti-tumor prenylated indole alkaloid from the fungus Aspergillus japonicus TE-739D.

Prenylated indole alkaloids, which are mainly produced by genera Aspergillus and Penicillium, are a class of structurally intriguing specialized metabolites with remarkable biomedical interests. In this study, chemically guided isolation of the Nicotiana tabacum-derived endophytic fungus Aspergillus japonicus TE-739D yielded eight structurally diverse prenylated indole alkaloids, including an undescribed compound, namely aspertaichamide B (ATB, 1), together with seven previously discovered derivatives (compounds 2 - 8). Their chemical structures as well as the stereochemical features were determined by integrated spectroscopic analyses, including HRESIMS, NMR, NMR calculations with DP4 + probability analysis, and a comparison of the experimental ECD data with computed DFT-based quantum chemical calculations. In vitro cytotoxic effects against the gastric cancer MFC cells revealed that the new compound ATB demonstrated considerable activity. Further studies found that ATB suppressed the viability, colony formation, and migration ability of MFC cells, and induced MFC cells apoptosis in a concentration-dependent way. Moreover, ATB stimulated ROS production in MFC cells and inhibited the tumor growth in the MFC-sourced subcutaneous tumor model while not significantly reducing the weight of mice. The pharmacological results suggested that the newly discovered ATB may be a promising anti-tumor lead compound. KEY POINTS: • Eight structurally diverse prenylated indole alkaloids including a new aspertaichamide B (ATB) were isolated from the fungus Aspergillus japonicus TE-739D. • The structure of ATB was elucidated by HRESIMS, NMR, NMR calculations with DP4 + probability analysis, and ECD calculations. • ATB inhibited cell proliferation, promoted apoptosis, and increased ROS production in gastric cancer cells, and exhibited inhibitory effects on tumor growth in vivo.