6 June 2017

Thujone - a terpenoid

Natural toxin

Thujone is a natural toxin produced by many plant species e.g. Wormwood (Artemisia absinthium), Tansy (Tanacetum vulgare), Western red cedar (Thuja plicata), Sage (Salvia officinalis), and more.

α-thujone. Click image for 3D structure

Thujone is a monoterpene, i.e. built of two isoprene (C5) units and in addition has a ketone group. Thujone occur in plants in a mixture of α-thujone (CAS 546-80-5) and β-thujone (CAS 471-15-8) with the alpha form approx. 5 times more toxic or biological active.

Terpenes are volatile, especially monoterpenes and to some extent sesquiterpenes, and often has an odour as known from e.g. pine forests and culinary herbs. In plant science called essential oils.

Thujone and other terpenes are often bitter and functions as chemical defence against insect bite and damage to the plant tissue. Thujone interact with the GABA receptors and thus important in regulation of stimuli in our neural system. This mechanism is most known for Absinth where thujone is the active compound suspected for causing hallucinations and great inspiration for the artists around 1900 in Europe.

Western red cedar needles contain 4.6 mg kg-1 DW, equivalent to approx. 0.5% of the plant DW, and thereby being the dominant terpene for this species. For western red cedar monoculture stands typically 10-100 mg kg-1 DW is found for the litter layer and 0.2-2 mg kg-1 DW for the mineral soil horizons, summing up to 1-7 kg thujone pr ha. Toxicity for α-thujone is (LD50) 45 mg kg-1, log Kow is 2.03 and water solubility 670 mg L-1.

SMILES:

(α-thujone): O=C1[C@H](C)[C@@H]2[C@](C(C)C)(C1)C2

(β-thujone): C[C@@H]([C@@H](C2)[C@]2([C@@H](C)C)C1)C1=O

References:

  • Lachenmeier, D.W;. S.G. Walch; S.A. Padosch; L.U. Kroner (2006) Absinthe - A review. Critical Reviews in Food Science and Nutrition, 46, 365-377
  • Pelkonen, O.; K. Abass; & J. Wiesner (2013) Thujone and thujone-containing herbal medicinal and botanical products: Toxicological assessment. Regulatory Toxocology and Pharmacology, 65, 100-107
  • Strobel, B.W.; P.H. Jensen; L.H. Rasmussen; H.C.B Hansen (2005) Thujone in soil under Thuja plicata. Scandinavian Journal of Forst Research, 20, 7-11
  • Vourc’h, G.; J.L. Martin; P. Duncan; J. Escarré; & T.P. Clausen (2001) Defensive adaptations of Thuja plicata to ungulate browsing: a comparative study between mainland and island populations. Oecologia, 126, 84–93