Terpenes

Terpene hydrocarbons (Figure 2) are plant products, synthesized from isoprene units, that are found in the essential oils of plants (Trudgill 1994). Several mono-terpenes, sesquiterpenes, and triterpenes are transformed stereoselectively by fungi.

(+ )-a-Pinene from oil of turpentine is transformed by A. niger to (+ )-verbenone, (+ )-cis-verbenol, and (+ )-trans-sobrerol (Prema and Bhattacharyya 1962); by Armillariella mellea to (+ )-trans-sobrerol, (+ )-trans-verbenol, and (+ )-verbenone plus seven minor metabolites (Draczyriska et al. 1985); and by Penicillium sp. to verbenone (Agrawal and Joseph 2000). (— )-a-Pinene is converted by A. mellea

CH3-CH2-(CH2)n-CH2-COOH

Figure 1 Pathways for the oxidation of 1-alkenes by the yeast Yarrowia lipolytica (adapted from Klug and Markovetz 1968).

CH3-CH2-(CH2)n-CH2-COOH

Figure 1 Pathways for the oxidation of 1-alkenes by the yeast Yarrowia lipolytica (adapted from Klug and Markovetz 1968).

Figure 2 Structures of several terpene hydrocarbons and the steroid hydrocarbon stigmasta-3,5-diene.

to (— )-trans-sobrerol, (— )-verbenone, (— )-7-hydroxy-a-terpineol, and five other compounds (Draczynska et al. 1985) and by the yeast Hormonema sp. to trans-verbenol and verbenone (van Dyk et al. 1998). (— )-p-Pinene is transformed by A. mellea to trans-pinocarveol, isopinocam-phone, pinocarvone, and six minor metabolites (Draczynska et al. 1985) and by Hormonema sp. to pinocamphone and 3-hydroxypinocamphone (van Dyk et al. 1998).

b-Myrcene, from oil of bay, is transformed by A. niger, which adds two hydroxyl groups at any of the double bonds to form three isomeric diols (Yamazaki et al. 1988).

(+ )-Limonene, found in orange-peel oil, is transformed by yeasts and filamentous fungi to several products, including (+ )-isopiperitenone, (+ )-limonene trans-1,2-diol, (+ )-cis-carveol, (+ )-perillyl alcohol, (+ )-perillic acid, trans-isopiperitenol, and a-terpineol (de Oliveira and Strapasson 2000; Noma et al. 1992; van Rensburg et al. 1997; van Dyk et al. 1998). Penicillium digitatum converts it mainly to (+ )-a-terpineol (Tan et al. 1998). ( — )-Limonene is transformed by A. fumigatus to (— )-perillyl alcohol, (— )-limonene trans-1,2-diol, and (+ )-neodihydrocarveol (Noma et al. 1992). Corynespora cassiicola converts the (+) and (—) isomers of limonene mainly to (+)- and (— )-limonene trans-1,2-diol (Demyttenaere et al. 2001).

Several sesquiterpenes (Figure 2) are transformed by fungi. Calarene is oxidized by Diplodia gossypina at two of the ring carbons and one of the methyl groups of the cyclopropane ring (Abraham et al. 1992). b-Selinene, (+ )-aromadendrene, and its isomer (— )-alloaromadendrene are transformed by Glomerella cingulata to triols (Miyazawa et al. 1995; 1997) and (+)-g-gurjunene is transformed by G. cingulata to a diol and a triol (Miyazawa et al. 1998).

The triterpene squalene (Figure 2) and steroid hydrocarbons, such as stigmasta-3,5-diene, are among the lipophilic extractives in eucalyptus wood that have been found to be partially degraded by Phlebia radiata and other white-rot fungi (Martínez-Iñigo et al. 2000).

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