Volatile terpenoids and tropolones in heartwood extracts of yellow-cedar, Monterey cypress, and their hybrid Leyland cypress

Abstract

Leyland cypress, an intergeneric hybrid, produces the same volatile heartwood compounds as its parental taxa, yellow-cedar and Monterrey cypress. However, the proportion of total sesquiterpenes and some of the individual components appear unique to their respective heartwoods. Leyland cypress, xHesperotropsis leylandii is an intergeneric hybrid between yellow-cedar, Callitropsis nootkatensis, and Monterey cypress, Hesperocyparis macrocarpa. Their heartwoods are protected by bioactive compounds and rated very durable to durable for products used above ground. Several compounds in yellow-cedar and Monterrey cypress heartwoods are also active against various fungi, bacteria, human insect pests, and plant pathogens, whereas Leyland cypress heartwood has never been thoroughly investigated. The first aim for this study was to examine the volatile compounds in ethyl acetate extracts from the heartwood of all three tree species in Oregon. The second aim was to determine the extent Leyland cypress differs from its parental species, and further investigate any of its novel compounds for biological activity. Ethyl acetate extracts of fresh heartwood were prepared for three trees of each species and analyzed by gas chromatography. Thirty-three compounds were detected at 0.5 % or greater abundance across all species, and 23 were identified. Carvacrol was the major monoterpene and nootkatin the most abundant tropolone in all three species. Valencene 11, 12-diol and nootkatone topped the list of sesquiterpenes in yellow-cedar and Leyland cypress, respectively, whereas no sesquiterpenes were detected in Monterrey cypress. This appears to be the first report of tropolones hinokitiol, procerin, and nootkatin in Leyland cypress, α-thujaplicinol, pygmaein, and procerin in Monterrey cypress, and hinokitiol in yellow-cedar. Leyland cypress heartwood does not biosynthesize structurally unique compounds from those produced by its parental species, and is an unlikely source of novel biocides. However, the proportion of total sesquiterpenes and some of the individual components in Leyland cypress heartwood may distinguish it from the heartwood of its parental species.