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Antifungal terpenoid and troponoid analogues for wood durability enhancement

Aspects of the development of novel analogues of terpenoid and tropolone natural products with antifungal properties against important wood deteriorating fungi are reported. Antifungal wood extractives and essential oil components provided valuable leads in chemical syntheses toward novel compounds with potential as wood bio-protectants. Analogues of antifungal monoterpenoid and diterpenoid wood extractives were synthesised and tested for activity against wood damaging fungi. 1-Methyl-4-nonylcyclohexan-1-ol, an analogue of β-terpineol and 2-isopropyl-4-nonylphenol, an analogue of thymol were prepared from p-n-nonylanisole by multi-step syntheses. 2-Isopropyl-1-naphthol, a simplified analogue of totarol was prepared by C-isopropylation of β-naphthoxide. In antifungal activity assays, these terpenoid analogues showed good to moderate activity against the brown rot fungus Coniophora puteana but were, in general, only weakly active against the other test decay and staining fungi. A bio-activity led investigation of oxygenated sesquiterpenoids from the foliage essential oils of three New Zealand native softwoods, totara, rimu and kahikatea, identified caryophyllene oxide, humulene oxide II, globulol and a-cadinol as major components of fungistatic oil fractions. Based on these findings simple synthetic compounds with epoxide (4-nonylcyclohexan-1,2-epoxide) and tertiary alcohol functionalities (4-ethyl-1-methyl-1,2,3,4-tetrahydronaphth-1-ol and 5,9-dimethyl-6,7,8,9-tetrahydrobenzocyclohepten-5-ol) were synthesised by multi-step pathways. Bioassays against wood decay and sapstain fungi revealed these compounds possessed efficacies equal to, or in some cases superior to, the natural sesquiterpenoids. A range of known and novel tropolone compounds was prepared by adapted literature methods. 3-Carboxy-4-carboxymethyltropolone, prepared by oxidation of purpurogallin, was a key intermediate in the synthesis of 4-alkylcarboxytropolones, an alkyl δ-lactone tropolone, 4-alkenyl and 4-alkyltropolones and 4-styryltropolones. A new synthetic pathway to β-thujaplicin via oxidation of 1-methyl-3,4,6-trihydroxy-(5H)-benzocyclohepten-5-one was proposed and investigated, but proved unsuccessful. A series of novel 3-alkyltropolones were prepared by direct alkylation of tropolone and β-thujaplicin with diethyl acetals. 3-(1-Formylmethyl)tropolone, prepared by condensation of trans-hex-2-enal diethyl acetal with tropolone, proved a useful intermediate to tropolones with secondary functional groups. A selection of these synthetic tropolones exhibited potent antifungal properties against four wood damaging fungi, in particular Coniophora puteana. Efficacies were comparable to and, in certain cases, superior to the commercial wood preservative tri-n-butyltin napththenate (TBTN). The best performing of the tropolones was 3-(1-ethyl)butyltropolone. This compound exhibited greater fungitoxicity than TBTN against the white rot and soft rot test fungi and was of comparable activity to the commercial antisapstain agent 3-iodo-2-propynyl butyl carbamate against the sapstain fungus Sphaeropsis sapinea.
Type of thesis
Torr, K. (2002). Antifungal terpenoid and troponoid analogues for wood durability enhancement (Thesis, Doctor of Philosophy (PhD)). The University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/14102
The University of Waikato
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