Penioxalicin, a novel 3-nor-2,3- seco -labdane type diterpene from the fungus Penicillium oxalicum TW01-1

Penioxalicin (1), the first 3-nor-2,3-seco-labdane type diterpene featuring the fission between C-2 and C-3 in the ring A and the decarboxylation at C-3, was isolated from the fungus Penicillium oxalicum TW01-1. Its planar structure and absolute configuration were elucidated mainly by analysis of 1D and 2D-NMR, ECD spectroscopic data, and single-crystal X-ray diffraction. Compound 1 showed moderate cytotoxicity against HL-60 cell line. The possible biosynthetic pathway of 1 was also proposed.