Fascicularones C and D, Tricyclo[5.4.0.02.5]undecane Sesquiterpenoids from the Liquid Culture of Naematoloma fasciculare

N. fasciculare is a poisonous mushroom widely distributed in northeast part of Japan (Japanese name: Nigakuritake). Phytochemical investigation of this mushroom revealed some biologically active compounds which include new lanostane-type triterpenoids, fasciculols A-F [1 – 3]. In addition, N. fasciculare, when grown in liquid culture, produced a complex mixture of sesquiterpene metabolites of a new structural skeleton. Previously, Ito et al. and Doi et al. have reported the isolation and structure elucidation of some ring fused new sesquiterpenes, naematolin possessing cytotoxicity [4] and naematolins B, C (1) and G (2) [5 – 7] from the liquid culture filtrates of this fungus. These naematolins C (1) and G (2), tricyclo[5.4.0.02,5]undecane sesquiterpenoids, have attracted considerable attention due to their molecular complexity and intriguing biosynthesis. In our continuing search for chemical constituents from the mycelial culture of this fungus, we have isolated two novel sesquiterpenoids named fascicularones A (3) and B (4) having tricyclic ring skeleton [8]. Further investigation for metabolites of this fungal strain in detail let to the isolation of two fascicularone related compounds, fascicularones C (5) and D (6). This paper describes the isolation and structure elucidation of 5 and 6.