Non-geminal Aliphatic Dihalogenation Pattern in Dichlorinated Diaporthins from Hamigera fusca NRRL 35721.

Two new epimeric dihalogenated diaporthins, (9 R * )-8-methyl-9,11-dichlorodiaporthin (2) and (9 S * )-8-methyl-9,11-dichlorodiaporthin (3), have been isolated from the soil fungus Hamigera fusca NRRL 35721 alongside the known regioisomeric isocoumarin 8-methyl-11,11-dichlorodiaporthin (1). Their structures were elucidated by high-resolution mass spectrometry and NMR spectroscopy combined with molecular modeling. Compounds 1-3 are the first isocoumarins and the first halogenated metabolites ever reported from the Hamigera genus. The new compounds 2 and 3 display a non-geminal aliphatic dichlorination pattern unprecedented among known fungal dihalogenated aromatic polyketides. A bifunctional methyltransferase/aliphatic halogenase flavoenzyme is proposed to be involved in the biosynthesis of dichlorinated diaporthins 1-3. These metabolites are weakly cytotoxic.