Two new pterosin dimers from Pteris mutifida Poir.

Two new C₁₄ pterosin dimers, which are a pair of isomers named as bimutipterosins A (1) and B (2), were isolated from the whole plant of Pteris multifida. Their structures have been elucidated on the basis of NMR and MS data. From a biogenetic point of view, these compounds including a cyclobutane basic core should be considered as a [2+2] dimerization product of dehydropterosin Q, which was a known compound and also isolated from this plant. This novel type of pterosin dimer was reported here for the first time. Compounds 1 and 2 showed cytotoxicity against HL 60 cell line (human leukemia) with the IC₅₀ values of 12.8 and 26.6 μM, respectively.