(-)-Rugulosin is the optical isomer of the mycotoxin, (+)-Rugulosin, which was first isolated from Myrothecium verrucaria in 1968. The isomers appear not to be co-produced but both occur widely in several fungal genera. (-)-Rugulosin has been shown to have antiviral properties. (-)-Rugulosin is the less common and less studied isomer, and there are few comparative studies of the relative potency of the isomers.