Neobulgarones A∼F from cultures of Neobulgaria pura, new inhibitors of appressorium formation of Magnaporthe grisea

Six new dimeric anthraquinone derivatives, neobulgarones A (3a), B (3b), C (4a), D (4b), E (5a) and F (5b), were isolated from the mycelia of the ascomycete Neobulgaria pura together with the monomeric carviolin (I) and 1-O-methylemodin (2). All new compounds inhibited the formation of appressoria in germinating conidia of Magnaporthe grisea on inductive (hydrophobic) surface. The compounds exhibited moderate cytotoxic, but no antifungal, antibacterial, or phytotoxic activities.