17(E)-13α(H)-Malabarica-14(27),17,21-triene, an unexpected tricyclic hydrocarbon in sediments

17(E)-13α(H)-malabarica-14(27),17,21-triene has been isolated from the solvent extract of a recent sediment from a sulfur-rich meromictic lake (Lake Cadagno, Switzerland) and its structure unambiguously established by NMR studies. This tricyclic triterpenoid, with a rare hydrocarbon skeleton, may originate from algal or bacterial biological precursors which remain to be discovered.