Immunosuppressive Nor-isopimarane Diterpenes from Cultures of the Fungicolous Fungus HFG1018.

Eighteen new nor-isopimarane diterpenes, xylarinorditerpenes A-R (-), along with two previously reported compounds, 14α,16-epoxy-18-norisopimar-7-en-4α-ol () and the labdane-type diterpene agatadiol (), were isolated from cultures of the fungicolous fungus HFG1018 isolated from the wood-rotting basidiomycete . The structure elucidation and relative configuration assignments of - were accomplished by interpretation of spectroscopic data and through computational methods. The absolute configurations of , , and were determined by single-crystal X-ray diffraction. Compounds - possess an 18- or 19-nor-isopimarane skeleton, and compounds and possess an 18,19-dinor-isopimarane skeleton. Compounds -, , , , and showed immunosuppressive activity but were devoid of cytotoxicity against the cell proliferation by concanavalin A-induced T lymphocytes and lipopolysaccharide-induced B lymphocytes, with IC values varying from 1.0 to 27.2 μM and from 16.1 to 51.8 μM, respectively.