Diterpenes from the brown algae Dictyota dichotoma and Dictyota linearis

The new diterpenes, isopachydictyolal ( 1) from D. dichotoma and 4α-acetyldictyodial ( 2) from D. linearis were isolated, using chromatographic techniques, and their chemical structures were elucidated on the basis of their NMR and mass spectral data. Nineteen secondary metabolites of the brown alga Dictyota dichotoma (Huds.) Lam. and fifteen metabolites of the brown alga D. linearis (Ag.) Grev. were isolated and their chemical structures were elucidated on the basis of their NMR and mass spectral data. The diterpenes isopachydictyolal ( 1) from D. dichotoma and 4α-acetyldictyodial ( 2) from D. linearis are new natural products. The antiviral activity of metabolites isolated in adequate amounts was evaluated in laboratory assays against Herpes simplex virus I (HSV I) and Poliomyelitis Virus I, using Vero cells as hosts.