From our search for compounds from marine organisms with potential pharmacological utility, a violet pigment that exhibits antitumor, antiviral, and immunomodulatory properties in vitro and antitumor properties in vivo was discovered. From spectroscopic analysis, including long-range ¹H-¹³C correlation and natural abundance ¹³C-¹³C NMR experiments, the structure elucidation of this fused pentacyclic aromatic alkaloid, which we have designated dercitin (1), was achieved. This alkaloid represents a unique variation on fused-ring alkaloids previously found in marine organisms. Shipboard extraction (3:1 MeOH-toluene) and screening of fresh sponge material, collected by manned submersible at 160 m near Goulding Cay, Bahamas, showed significant in vitro activity against P388 murine leukemia cells. Subsequent bioassay guided fractionation of the MeOH extract of the frozen sponge lead to the isolation of 1 as the active principle (0.01%) as well as 1,1-dimethyl-5,6-dihydroxyindolinium chloride, which is inactive in our assays. Optimized extraction of the sponge with a mixture of NH₄OH (5%) and CH₂Cl₂ followed by purification with CCCC gave 1 in improved yield (0.69% of wet wt) as a deep violet powder (mp 168 °C). This is the first report of a pentacylic aromatic alkaloid bearing the thiazole functionality. The term fenestrae was introduced in 1972 by Georgian and Saltzman for tetracyclo[3.3.1.0³·⁹.0⁷·⁹]nonane, a hydrocarbon of considerable theoretical interest due to the expected planar geometry of its central carbon atom. The novel synthetic problems posed by this tetracycle and, more generally, by other rosettanes have attracted much attention, which has been further stimulated by the 1979 report of the first naturally occurring member of this novel class, lauren-1-ene (1). We describe herein a total synthesis of 1, which represents an unprecedentedly concise and stereocontrolled solution to this problem. This synthesis is based on the most complex example of an arene-olefin meta photocycloaddition reported to date and provides a novel and general strategy for the synthesis of analogous rosettanes.