Eight known abietane-type diterpenes were isolated from the weak acidic fraction of the n-hexane extract from cones of Taxodium distichum, one of the extant, living fossil conifers. They were identified as 6,7-dehydroroyleanone (1), taxodal (2), taxodione (3), salvinolone (4), 14-deoxycoleon U (5), 5,6-dehydrosugiol (6), sandaracopimaric acid (7), and xanthoperol (8). The structures of these compounds were determined by comparison of NMR spectral data with published data. The antitermitic (termicidal and antifeedant) activities of the compounds 1-8 against the subterranean termite, Reticulitermes speratus Kolbe, were evaluated. Compounds 1 and 3 showed potent termicidal activity, and 5 and 8 showed potent antifeedant activity. Compound 1 was found to be one of the representative bioactive compounds in the n-hexane extract of T. distichum cones. Compounds 1-8, with the exception of 7, were oxides of ferruginol (9). Therefore, the presence of various oxidation forms of the abietane-type structure reflects their various bioactivities.

Summary The antifungal properties of 14 major oleoresin‐constitutive terpenoids of Norway spruce (Picea abies) against Heterobasidion parviporum were evaluated in vitro at three gradient concentrations, 0.1, 0.2 and 0.4 μmol/cm2, on potato dextrose agar medium. Eight monoterpene hydrocarbons (+)‐ and (−)‐α‐pinene, (−)‐β‐pinene, (+)‐3‐carene, myrcene, (+)‐ and (−)‐limonene, terpinolene; four oxygenated monoterpenes α‐terpineol, terpinen‐4‐ol, 1,8‐cineole, bornyl acetate; and two resin acids abietic acid and dehydroabietic acid were selected. Abietic and dehydroabietic acids showed the highest antifungal activities at all concentrations. Among oxygenated monoterpenes, bornyl acetate and α‐terpineol showed antifungal activity at the highest concentration. Among monoterpene hydrocarbons, (+)‐α‐pinene showed similar activity to terpinen‐4‐ol and 1,8‐cineole at the highest concentration; however, it was lower than α‐terpineol and bornyl acetate. Other monoterpene hydrocarbons inhibited mycelial growth by <10%. Re‐extraction of medium surfaces after the test period revealed that most α‐terpineol and terpinen‐4‐ol remained unchanged on the surface but monoterpene hydrocarbons completely disappeared. However, notable fungal transformed products were observed on surfaces applied with 1,8‐cineole and bornyl acetate. Thus, mycelial growth inhibition of monoterpenoids might be caused by complex functions such as biodegradation and/or detoxification by interaction between mycelium and compound. These results provide a basis for future studies considering the role of chemodiversity in the comprehensive chemical defence of P. abies.

The chemical composition of Taxodium distichum cones and the antifungal activities of twelve diterpenoids against two wood decay fungi, Trametes versicolor (white-rot) and Fomitopsis palustris (brown-rot) were examined. The chemical composition of the major extractive fraction, the n-C(6)H(14) extract, was evaluated and its antifungal properties were identified. Twelve diterpenoids including ten abietane-type components were isolated from the n-C(6)H(14) extract: 6,7-dehydroferruginol (1), ferruginol (2), 6,7-dehydroroyleanone (3), sandaracopimaric acid (4), taxodione (5), taxodal (6), taxodone (7), sugiol (8), xanthoperol (9), salvinolone (10), 5,6-dehydrosugiol (11), and 14-deoxycoleon U (12). Compounds 5 and 12 were highly active against both wood-decay fungi. In particular, the activities of these compounds against F. palustris were potent. The results suggest that the position and the number of hydroxyl groups on abietane-type structures may be related to antifungal activities against T. versicolor and F. palustris.