Frankincense: NMR IDs cis and trans

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  • Published: Nov 1, 2016
  • Author: David Bradley
  • Channels: NMR Knowledge Base
thumbnail image: Frankincense: NMR IDs cis and trans

Frankly, my dear

Boswellia, Frankincense from Wiki: Franz Eugen Köhler, Köhler's Medizinal-Pflanzen (+)-cis- and (+)-trans-Olibanic Acids as Key Odorants of Frankincense.

You could usually predict the arrival of the Queen of Sheba for the unmistakable aroma of her scent - frankincense. Now, French scientists have used nuclear magnetic resonance (NMR) spectroscopy to identify the two main odour components of this centuries-old perfume and dubbed them (+)-cis- and (+)-trans-olibanic acids.

Frankincense is perhaps one of the oldest and most well-known fragrances in the world having been favoured for religious ceremonies and mythologized in several texts through the centuries. Now, Nicolas Baldovini and his colleagues at the Institut de chimie de Nice (CNRS/UNS), France, have at last pinpointed the compounds that give this material its distinctive aroma. The team describes their NMR study of frankincense and the identification of two molecules, olibanic acids in the Wiley journal Angewandte Chemie.

Frankincense, also known as olibanum, is the resinous gum, or sap, that leaks from the bark of Boswellia trees found in countries on the Red Sea and the Gulf of Aden. It has been used for more than 6,000 years by countless civilizations, from Mesopotamia to the present day and is mentioned at least twenty times in The Bible, most famously as one of the gifts offered by the "Three Wise Men" in the story of the birth of Christ. It is commonly burned during religious ceremonies for its sweet, strong smell. However, despite several thousand years of olfactory history and endless research efforts it is only now that the precise nature of the odorant molecules in frankincense have been identified.

Cis and Trans at PPM

Baldovini and his team specialize in fragrances and explain that the main obstacle to identifying the scent of frankincense at the molecular level lay in the fact that these compounds are present only at concentrations of a few hundred parts per million (ppm). As such, the team started with approximately three kilograms of the essential oil from frankincense sourced in Somalia. They were able to extract a mere 1 milligram of odorant chemical and a series of distillations, extractions, and chromatographic analyses was needed to home in on the chemical suspects. They had to recruit odour specialists to know for certain that their extract was the precise scent of frankincense. Even with major advances in sensor technology, the expert human nose remains the most able to detect the tiniest quantities of the pertinent constituents in a sample.

Perfume potential

However, the team then turned to NMR to pull out the structures. The two molecules, which give frankincense what the team describes as its "old church" smell are identified as (+)-trans- and (+)-cis-2- octylcyclopropyl-1-carboxylic acids. Intriguingly, for such relatively simple molecules this is the first time that this pair has been seen in a natural extract. "These cyclopropyl-derived acids provide the very characteristic old churchlike endnote of the frankincense odour," the team reports. Of course, to validate their spectra, the team then synthesised the compounds and ran the spectroscopy again; they showed that the synthesised compounds were identical to the natural components.

The identification of the olibanic acids in frankincense could allow synthetic, and so much cheaper and more readily available, products with the same odour to be made. Moreover, structural novelty and molecular diversity are always of interest to medicinal chemists. Given that there has been some research into the physiological activity of frankincense, it would be interesting to test these particular components against an array of medically relevant assays to see whether they have any prospect of being developed as pharmaceuticals.

Related Links

Angew Chem Int Edn Engl 2016, online: "(+)-cis- and (+)-trans-Olibanic Acids as Key Odorants of Frankincense."

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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