Nectriafurone, a naturally occurring isofuranonaphthoquinone was isolated in 1983 from the fungus nectria haematococca.30 Fungi have been treated as the richest source of this class of natural products. Pestacin, the first member of phthalan natural products was isolated as a racemic mixture from the microorganism pestalotiopsis microspora, contains dihydrofuran nucleus as the key structure.31Halenaquinone (Figure 1.8), an antibiotic having furan-fused pentacyclic skeleton, has been found in a tropical marine sponge of Xestospongia exigua collected in western caroline islands 32 and its sodium salt showed interesting antiviral activities. The furanoditerpenes, spongiadiol (Figure 1.8) isolated from the deep water Carribbean sponge, Spongia
