Ethylnaphthoquinone derivatives as inhibitors of indoleamine-2, 3-dioxygenase from the mangrove endophytic fungus Neofusicoccum austral SYSU-SKS024.

Bioassay-guided fractionation of the dichloromethane extract of the fungus Neofusicoccum austral SYSU-SKS024 led to the isolation of three new ethylnaphthoquinone derivatives, neofusnaphthoquinone A ( 1 ), 6-(1-methoxylethy1)-2,7-dimethoxyjuglone ( 2 ), (3 R ,4 R )-3-methoxyl-botryosphaerone D ( 6 ), together with six known analogs ( 3 – 5 and 7 – 9 ). Their structures were elucidated by spectroscopic analysis and single crystal X-ray diffraction analysis. Neofusnaphthoquinone A ( 1 ) is the third example of the unsymmetrical naphthoquinone dimer, which is rarely found in natural source. All of the isolates were evaluated for their indoleamine 2, 3-dioxygenase (IDO) inhibitory activity, compounds 1 – 6 showed in vitro inhibitory effects against IDO with IC 50 values ranging from 0.11 to 10.92 μM. This is the first time naphthoquinone dimer ( 1 ), as a novel carbon skeleton possessing IDO inhibitory activity, was reported. [ABSTRACT FROM AUTHOR]