Heptaketides with antiviral activity from three endolichenic fungal strains Nigrospora sp., Alternaria sp. and Phialophora sp.

Two new heptaketides, (+)-(2S,3S,4aS)-altenuene (1a) and (-)-(2S,3S,4aR)-isoaltenuene (2a), together with six known compounds, (-)-(2R,3R,4aR)-altenuene (1b), (+)-(2R,3R,4aS)-isoaltenuene (2b), 5'-methoxy-6-methyl-biphenyl-3,4,3'-triol (3), alternariol (4), alternariol-9-methyl ether (5), and 4-hydroxyalternariol-9-methyl ether (6) were isolated from the EtOAc extract of an endolichenic fungal strain Nigrospora sphaerica (No.83-1-1-2). Compounds 1a and 1b were separated from enantiomers 1 by chiral HPLC, and so were 2a and 2b from enantiomers 2. Interestingly, 1-6 were also obtained from other two endolichenic fungal strains Alternaria alternata (No.58-8-4-1) and Phialophora sp. (No.96-1-8-1). The structures of 1-6 were elucidated by means of MS, HR-MS, NMR, and X-ray diffraction. Furthermore, the absolute configurations of 1a-2b were determined by CD experiments and CD calculation. Of these compounds, 4 and 5 showed antiviral activity against herpes simplex virus (HSV) in vitro, with IC(50) values of 13.5 and 21.3 μM, and with selective index (SI) values of 26.5 and 17.1, respectively.