Abietane and C20-Norabietane Diterpenes from the Stem Bark of Fraxinus sieboldiana and Their Biological Activities

Fourteen new abietane (1-14) and seven new C(20)-norabietane (15-21) diterpenes, together with five known analogues, have been isolated from the stem bark of Fraxinus sieboldiana. Their structures were elucidated by spectroscopic data analysis. In the in vitro assays, at 10(-5) M, compounds 8, 16, and 22 showed inhibitory activity against the release of β-glucuronidase in rat polymorphonuclear leukocytes induced by platelet-activating factor, with 59.7 ± 4.8%, 56.1 ± 5.6%, and 65.9 ± 3.1% inhibition, respectively. Compound 23 was active against H5N1 avian influenza virus with an IC(50) value of 4.8 μM. Compounds 3 and 5 exhibited selective cytotoxic activities against A2780 (IC(50) 1.7 μM) and A549 (IC(50) 6.0 μM), respectively.