Hispidulones A and B, two new phenalenone analogs from desert plant endophytic fungus Chaetosphaeronema hispidulum.

Two new phenalenone analogs hispidulones A (1) and B (2) were isolated from the specially bioenvironmental desert plant endophytic fungus Chaetosphaeronema hispidulum. The structure of these two compounds were elucidated by extensive spectra analysis including HR-ESI-MS, NMR (1H, 13C, 1H-1H COSY, HSQC, and HMBC), CD, and electronic circular dichroism (ECD) combined with quantum-chemical calculations adopting time-dependent density functional theory (TDDFT) approaches. The W long-ranged 1H-1H COSY and HMBC correlations are very important in the structural elucidation of these two compounds. Hispidulone A (1) possesses a cyclohexa-2,5-dien-1-one moiety, whereas hispidulone B (2) contains a hemiacetal OCH3 group, which are very rare in the structures of phenalenone analogs. According to structural features of these two compounds together considering the literature, the possible biosynthetic pathway of 1 and 2 was postulated. Hispidulone B (2) displayed cytotoxic activities against three cancer cell lines A549, Huh7, and HeLa with IC50 values of 2.71 ± 0.08, 22.93 ± 1.61, and 23.94 ± 0.33 μM.