Chemical Compositions and Enantiomeric Distributions of Foliar Essential Oils of Chamaecyparis lawsoniana (A. Murray bis) Parl, Thuja plicata Donn ex D. Don, and Tsuga heterophylla Sarg.

Abstract

As part of our continuing interest in the essential oil compositions of gymnosperms, particularly the distribution of chiral terpenoids, we have obtained the foliar essential oils of Chamaecyparis lawsoniana (two samples), Thuja plicata (three samples), and Tsuga heterophylla (six samples) from locations in the state of Oregon, USA. The essential oils were obtained via hydrodistillation and analyzed by gas chromatographic techniques, including chiral gas chromatography—mass spectrometry. The major components in C. lawsoniana foliar essential oil were limonene (27.4% and 22.0%; >99% (+)-limonene), oplopanonyl acetate (13.8% and 11.3%), beyerene (14.3% and 9.0%), sabinene (7.0% and 6.5%; >99% (+)-sabinene), terpinen-4-ol (5.0% and 5.3%; predominantly (+)-terpinen-4-ol), and methyl myrtenate (2.0% and 5.4%). The major components in T. plicata essential oil were (−)-α-thujone (67.1–74.6%), (+)-β-thujone (7.8–9.3%), terpinen-4-ol (2.7–4.4%; predominantly (+)-terpinen-4-ol), and (+)-sabinene (1.1–3.5%). The major components in T. heterophylla essential oil were myrcene (7.0–27.6%), α-pinene (14.4–27.2%), β-phellandrene (6.6–19.3%), β-pinene (6.4–14.9%; >90% (−)-β-pinene), and (Z)-β-ocimene (0.7–11.3%). There are significant differences between the C. lawsoniana essential oils from wild trees in Oregon and those of trees cultivated in other geographical locations. The essential oil compositions of T. plicata are very similar, regardless of the collection site. There are no significant differences between T. heterophylla essential oils from the Oregon Coastal Range or those from the Oregon Cascade Range. Comparing essential oils of the Cupressaceae with the Pinaceae, there are some developing trends. The (+)-enantiomers seem to dominate for α-pinene, camphene, sabinene, β-pinene, limonene, terpinen-4-ol, and α-terpineol in the Cuppressaceae. On the other hand, the (−)-enantiomers seem to predominate for α-pinene, camphene, β-pinene, limonene, β-phellandrene, terpinen-4-ol, and α-terpineol in the Pinaceae.