The smell of Christmas

The discovery of molecules responsible for the smell of frankincense may revolutionise the perfume industry and save a species

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The distinctive and lingering smell of frankincense overflows from Oxford’s numerous old churches at Oxmas time, heralding the approach of Christmas.

Researchers at the Institute de Chimie de Nice in France have recently distilled two new “highly potent and substantive odorants” in frankincense, present in fewer than 100 parts per million—the equivalent of a pinch of salt in ten tonnes of crisps. The implications of this discovery are revolutionary for the perfumery world and may even prevent the extinction of the species of tree from which frankincense resin is extracted.

The elusive molecules are named, somewhat unromantically, (1S,2S)-(+)-trans- and (1S,2R)-(+)-cis-2-octylcyclopropyl-1-carboxylic acid. Intensive research by the Baldovini group led to the eventual isolation of the cyclopropyl acid derivatives responsible for the basenotes, the longest lasting oils, of the famous scent widely used in the fragrance industry.

“We have patented the use of these compounds for fragrance formulation and plan to find a way to commercialise these acids as fragrance ingredients for perfumers,” stated Nicolas Baldovini, research leader, about the commercial aspects to this discovery.

Perfumery, or ‘per fumum’—through smoke, a reference to the release of fragrant chemicals through burning—is considered one of the earliest forms of chemistry. The frankincense resin, olibamum, which produces the scent in many popular scented products is believed to be one of the first aromatic materials used by mankind, dating back more than four millenia. Indeed, frankincense resins have been of huge social, economic, and religious importance throughout history, perhaps most famously as one of the presents offered to the infant Christ by the three kings in the Bible.

Baldovini’s desire to understand the chemical basis of ancient natural products used extensively in perfumery stems from the fact that “there is paradoxically little information on many raw materials concerning their impact odorants.” In other words, despite the extensive use of natural materials in perfumery, there is still a lack of research done to identify the constituent aromatic chemical molecules crucial to the scent that will allow artificial synthesize of the perfumes.

Despite nearly a millennium of use, the chemicals giving the strongest basenotes in frankincense products could, until now, only be distilled from natural resins collected by slashing the bark of the Boswellia sacra trees, unusual for their ability to grow out of solid rock.

Starting with three kilograms of frankincense resin from Somalia, Baldovini and his team isolated and purified approximately one milligram of the two carboxylic acid derivatives believed to give the incense its distinctive smell. Trained perfumers were used to confirm that the basenotes of frankincense were indeed given by the two molecules. Despite today’s unprecedented rate of technological advancement, our human nose is still the only instrument sensitive enough to detect the key components present in minute quantities in such mixtures. When used in conjuncture with analytical machines such as the Gas Chromatography Mass Spectrometer (GC-MS) or the Gas Chromatography-Olfactometer (GC-O) to determine the structure of the molecules present, the aromatic molecules are identified and their structures pinpointed.

The simple and economical chemical procedures used by the Baldovini group demonstrates that “natural aromatic raw materials are still poorly known goldmines.”

Recent studies in Ethiopia have shown that the overexploitation of frankincense-producing Boswellia could culminate in the loss of the entire species since intensive tapping causes the trees to divert too much of their carbohydrate stores into resin rather than for flowering and seed production.

“The trees, once damaged, do not regenerate. Fifty years from now, 90 percent of the Boswellia will be gone,” predicts Frans Bongers, Professor of Tropical Forest Ecology at Wageningen University.

Successful isolation of molecules providing the “characteristic old, churchlike basenote of the frankincense odour” as so aptly described by Baldovini, could allow cheaper and more readily available synthetic equivalents to be made artificially, preventing the otherwise inevitable extinction of Boswellia sacra because of commercial exploitation.