SummaryThe structure of a colorless dimer (4a) of puupehenone (l), which was isolated from Pacific marine sponges, has been elucidated from spectral data.Marine sponges are a rich source of secondary metabolites, particularly terpenoids [ 11. Occasionally, compounds of mixed biosynthesis have been encountered, among them the puupehenones 1-3, which are constructed of sesquiterpene and benzene moieties [2]. The yellow encrusting sponge, identified as Heteronenza sp. (family Spongiidue, order Dictyoceratidu, class Demospongiae), from which puupehenone (1) was originally isolated, was first collected by us off the Hawaiian islands of Lanai and Oahu. The halopuupehenones 2 and 3 were minor constituents in a Heteronemu sample from Enewetak in the Marshall islands. In all collections we encountered several dimeric compounds, some of them highly colored. A colorless dimer, bispuupehenone (4a). was subsequently also isolated from a Tahitian sponge, Hjrtios (= Inodes) eubumma (family Thorectidae, order Dictyoceratida), and is the subject of this report.H. eubumma was preserved in EtOH and then further extracted with the same solvent. The aqueous residue was partitioned with cyclohexane. Chromatography of the organic residue on Sephadex, then silica gel, yielded puupehenone (1) and bispuupehenone (4a), m.p. 234-240". A composition of C42H5406 was ascertained by mass spectrometry. The fragmentation pattern, including abundant M + -15 (m/z 639) and M + -151 (see wiggly line in 4) ions, were reminiscent of the puupehenone spectrum [2]. The presence of OH-groups was indicated by IR bands at 3560 and 3420 cm-I.The I3C-NMR spectrum displayed 2 1 signals, thus confirming that bispuupehenone (4a),is a symmetrical dimer of 1. Fifteen upfield signals parallel those of other drimane derivatives, e.g. 1, its methanol adduct 5, or 8-epichromazonarol (6) [3] I )