Bioactive spirobisnaphthalenes from the endophytic fungus Berkleasmium sp.

Nine new spirobisnaphthalenes, palmarumycins B1-B9 (1-9), along with 13 known compounds (10-22), were isolated from cultures of the fungus Berkleasmium sp., an endophyte isolated from the medicinal plant Dioscorea zingiberensis C. H. Wright. The structures of the new compounds were elucidated by analysis of the 1D and 2D NMR and HRESIMS spectra and by comparison with known compounds. Compounds 7-9 contain an uncommon 2,3-dihydro-1H-inden-1-one unit. All isolated compounds were evaluated for their antibacterial activities against Bacillus subtilis, Staphylococcus hemolyticus, Agrobacterium tumefaciens, Pseudomonas lachrymans, Ralstonia solanacearum, and Xanthomonas vesicatoria and for their antifungal effects against the spore germination of Magnaporthe oryzae. Palmarumycin C8 (22) exhibited the best antibacterial and antifungal effects. In addition, diepoxin δ (11) and palmarumycin C8 (22) showed pronounced cytotoxic activities against five human cancer cell lines (HCT-8, Bel-7402, BGC-823, A 549, A 2780) with IC50 values of 1.28-5.83 μM.