Isoprenyl phenyl ethers from liverworts of the genus Trichocolea: Cytotoxic activity, structural corrections, and synthesis

The main cytotoxic component in New Zealand collections of the liverwort Trichocolea mollissima was identified as methyl 4-[(5-oxogeranyl)oxy]-3-methoxybenzoate, a structure that has not been reported previously. Two double-bond isomers of this geranyl ether were present at lower levels. Reinvestigation of the benzoates from Japanese collections of Trichocolea tomentella led to the identification of four geranyl ethers (including two of the three compounds identified from T. mollissima), which had previously been assigned incorrect geranyl ester structures. One compound, previously reported as a 3,3-dimethylallyl ester, could not be reisolated from T. tomentella, but was found in a New Zealand collection of Trichocolea lanata. It was shown to be a 3,3-dimethylallyl ether by synthesis from methyl vanillate. Several of these compounds were active in cytotoxic and antifungal assays.