What molecules are we?
Frankincense, also called olibanum, is a resin obtained from trees in the genus Boswellia that grow in Africa and Asia. One of the first aromatic materials used by humans, it dates to the late fourth millennium BCE. It and myrrh1 are familiar as gifts offered to the Christ child by the Magi in the Christian gospel.
Surprisingly, the main odor ingredients in frankincense were only recently discovered. In the 2016 seminal article on this discovery, Nicolas Baldovini and collaborators at the University of Nice Sophia Antipolis (France), Albert Vieille SA (Vallauris, France), and the University of Turin (Italy) reported the isolation and characterization of (+)-cis- and (+)-trans-2-octylcyclopropanecarboxylic acids, which they called olibanic acids after frankincense’s alternative name. The 3-D image above represents the more fragrant cis isomer.
The olibanic acids constitute only ≈0.2 wt% of the oil derived from frankincense; but the authors’ olfactory tests showed that they are responsible for the aroma of the resin, which they describe as the “smell of old churches”. The researchers synthesized the two (+)-diastereomers as well as their (–)-counterparts, which do not exist in frankincense. The synthetic (+)-diastereomers are identical with the natural compounds that were extracted from B. carterii and B. frereana, species that grow in mountainous regions on both sides of the Gulf of Aden and the Red Sea.
This holiday season, give thanks to Baldovini and his colleagues for solving the mystery of frankincense!
1. See next week’s Molecule of the Week.
Learn more about this molecule from CAS, the most authoritative and comprehensive source for chemical information.