Alpha-muurolene, or α-muurolene, is part of the cadinene sesquiterpenoid family. Sesquiterpenoids are terpenes with three consecutive isoprene units. Cadinenes are bicyclic sesquiterpenoids. Notably, cadinenes have demonstrated some antifungal properties and potential as natural fungicides. 
Image Credits: CAS
Alpha-muurolene has been found in cinnamon and Inula helenium (horse-heal, see header image) root extracts, the latter of which have antioxidant properties, so perhaps further studies will discover something promising in that regard.  The concentration of α-muurolene and its oxidation products have been observed during the wet and dry seasons in central Amazonia, with mean concentrations of 1.50 nanograms per cubic meter (ng/m3) and 1.45 ng/m3, respectively. 
Alpha-muurolene is a central component in the essential oil from wood of Phoebe bournei (Yang, pictured below) at 7.32%. This wood has demonstrated some antitumor, antibacterial, and hypoglycemic properties, so the terpene’s relatively significant presence is promising.  Alpha-muurolene has been detected in essential oils from Hyptis monticola, a wild Brazilian plant species from high altitude with some antibacterial and antifungal properties, accounting for 6.4% of its contents. 
Phoebe bournei Image Credit: Earth.com
Furthermore, the terpene turned out to be one of the most abundant constituents of air-dried and conventionally dried Cryptomeria japonica (Japanese cedar) wood, which is a clear indicator of the nature of its aroma and aligns with the prevailing wisdom that α-muurolene’s scent is woody with hints of pine and citrus. 
Alpha-muurolene even showed up in Moutai, a Chinese liquor, along with quite a few other terpenes.  Considering the aromatic connotations that drinks from the far East tend to conjure, we might see our terpene in question in other fragrant concoctions of various natures.
For now, α-muurolene remains mostly a rich-smelling mystery that makes episodic appearances in a wide variety of places that reveal glimpses of its potential. Hopefully, we’ll see more of it in the future.
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- Spiridon, et al. “Antioxidant and Chemical Properties of Inula helenium Root Extracts.” Open Chemistry, vol. 11, no. 10, 2013. Journal Impact Factor = 1.512; Times Cited = 20
- Yee, et al. “Observations of Sesquiterpenes and Their Oxidation Products in Central Amazonia During the Wet and Dry Seasons.” Chem. Phys., vol. 18, no.14, pp. 10433–10457, 2018. Journal Impact Factor = 5.668; Times Cited = 11
- Ning, et al. “Essential Oil Extracted from Wood of Phoebe bournei (Hemsl.) Yang: Chemical Constituents, Antitumor, Antibacterial, and Hypoglycemic Activities.” , vol.14, no.1, pp. 858-869. Journal Impact Factor = 5.807; Times Cited = 1
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- Ohira, et al. “Evaluation of Dried-wood Odors: Comparison Between Analytical and Sensory Data on Odors from Dried sugi (Cryptomeria japonica) ” Journal of Wood Science, vol. 55, no.2, 2009, pp 144–148. Journal Impact Factor = 1.523; Times Cited = 19
- Wang, et al. “Identification and Aroma Impact of Volatile Terpenes in Moutai Liquor.” International Journal of Food Properties, vol. 19, no.6, 2016, pp.1335-1352. Journal Impact Factor = 1.398; Times Cited = 11
Horse-Heal Header Image Credit: Rare Seeds