Antitumour lignans and cytotoxic resin acids from a New Zealand gymnosperm, Libocedrus plumosa.

The antitumour activity of a foliage extract of a New Zealand gymnosperm, Libocedrus plumosa, against P388 leukaemia cells was due to β-peltatin 3. Deoxypodophyllotoxin 1 and β-peltatin A-methyl ether 2, P388-active lignans previously reported in L. bidwillii, were found at lower levels. High levels of trans-communic acid 4 and sandaracopimaric acid 5 were found in the L. plumosa extract. These diterpene resin acids showed cytotoxic activity against BSC-1 cells. A rapid "chemical screening" method is described, which further characterises bioactive extracts. Chemical screening and mass spectroscopy results for the two Libocedrus species and for Cupressus macrocarpa suggested that the P388 activity of the latter species was also due to 1 and 2. Extracts of all three of these species inhibited tubulin polymerisation.