Composition of the essential oil of the Rhododendron tomentosum Harmaja from Estonia

Abstract

Wild Rhododendron tomentosum Harmaja shoots were collected from four localities of Estonia. Essential oils, isolated from dried samples by simultaneous distillation and extraction, were analysed using GC-FID and Gas chromatography–mass spectrometry methods. The yields of oils were in the range 0.14–0.87%. A total of 72 constituents, accounting for over 95% of the total oil yield, were identified. The major components in the all four oils studied were palustrol (15.9–53.5%), ledol (11.8–18.3%), γ-terpineol (0–31.2%), p-cymene (0.1–13.9%), lepalone (0.7–6.5%), lepalol (1.0–6.5%) and cyclocolorenone (1.0–6.4%). Two different chemotypes of R. tomentosum were found in Estonia and one of them was rich in palustrol (41.0–53.5%) and ledol (14.6–18.3%). The second chemotype, for the first time, was rich in γ-terpineol (24.7–31.2%) and contained less of palustrol (15.9–16.7%) and ledol (11.8–12.8%), but more p-cymene (12.5–13.9%). Also, γ-terpineol was identified for the first time in the oils of R. tomentosum.

Keywords::

• Ledum palustre L.
• Rhododendrum tomentosum Harmaja
• marsh rosemary
• essential oil
• chemotypes
• ledol
• palustrol

Acknowledgement

The authors gratefully acknowledge Mati Müürisepp, Ph.D., for performing GC–MS analysis.