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 IC50 values of 13.5 and 21.3 μM, and with selective index (SI) values of 26.5 and 17.1, respectively.

Two new heptaketides were isolated from three endolichenic fungal strains Nigrospora sp., Alternaria sp., and Phialophora sp. Their structures and antiviral activity are reported herein.153