Biological Activity of α-Thujaplicin, the Isomer of Hinokitiol

α-Thujaplicin, a minor component of Aomori Hiba (Thujopsis dolabrata SIEB. et ZUCC. var. hondai MAKINO), showed rather strong antifungal activity against seven kinds of plant-pathogenic fungi, their minimum inhibitory concentrations (MICs) being in the range of 12.0—50.0 μg/ml. α-Thujaplicin and hinokitiol (the major component of Aomori Hiba) also showed clear antibacterial activity against Legionella pneumophila SG 1 and L. pneumophila SG 3, and their MICs are in the range of 6.25—50 μg/ml. This compound showed strong insecticidal activity against Reticulitermes speratus [50%-lethal concentration (LC50): 0.02 g/m2], and it also had clear acaricidal activity against Dermatophagoides farinae (LC50: 0.66 g/m2). At 24 h after treatment, α-thujaplicin at 0.63 μg/ml inhibited the cell growth of murine P388 lymphocytic leukemia by 78%, and its cytotoxic activity at a concentration higher than 0.63 μg/ml was as high as that of vincristine, used as a positive control. On the other hand, the cytotoxic effect of α-thujaplicin at 0.63 μg/ml was weaker than that of vinblastine. In this respect, the strong cytotoxic effect of α-thujaplicin on murine P388 lymphocytic leukemia cell line should be emphasized, considering that it has recently been found to be low in toxicity to mice.