Bioactive Constituents of Thuja o ccidentalis

An ethyl acetate-soluble extract of the combined leaves and twigs of Thuja occidentalis was found to inhibit 12-O-tetradecanoylphorbol 13-acetate (TPA)-induced ornithine decarboxylase (ODC) in cultured mouse epidermal ME 308 cells. Bioassay-guided fractionation of this extract led to the isolation of six active constituents (1−6), namely, (+)-7-oxo-13-epi-pimara-14,15-dien-18-oic acid (1), (+)-7-oxo-13-epi-pimara-8,15-dien-18-oic acid (2), (+)-isopimaric acid (3), (1S,2S,3R)-(+)-isopicrodeoxypodophyllotoxin (4), (−)-deoxypodophyllotoxin (5), and (−)-deoxypodorhizone (6). Compounds 1 and 4 are new natural products, and their structures and stereochemistry were determined using spectroscopic methods. Compounds 1−6 were evaluated for inhibition of the transformation of murine epidermal JB6 cells, inhibition of ornithine decarboxylase induction with murine epidermal ME 308 cells, and cytotoxic activity against KB cells.