Steven John Rowland, Paul Andrew Sutton, Dominic Payne

In alcoholic solutions (tinctures), the tricyclic triterpenoid alcohol, ambrein, which is usually the main ingredient of the natural product ambergris, undergoes photo-oxidation to a number of odorous products. Such tinctures are valuable in perfumery.

Similar reactions are thought to occur in the marine environment, when flotsam and jetsam ambergris are exposed to sunlight. However, previous simulations of this process used artificial photosensitisers and did not include dark controls.

We therefore conducted experiments in which ambrein in seawater (~1666 mg L-1) containing a photosensitiser, forms of which are found naturally in ambergris (5, 10, 15, 20-tetraphenyl-21H, 23H-porphine copper (II); 1% of ambrein w/w), was exposed to simulated natural sunlight for experimental periods of up to 6 h (approximately equivalent to 48 h natural exposure, Florida midday, mid-summer sunlight). Dark controls were treated in the same manner, without exposure to light.

After 6 h exposure to light, total reaction products detectable by gas chromatography-mass spectrometry of solvent extracts, comprised about 1% by mass of the initial ambrein. However, unaccounted-for mass losses of ambrein were much greater than this (~50%), even in the dark, suggesting major losses of volatile products and/or non-recovery of some oxidation products by extraction. Photo-oxidation products included ambroxan, γ-dihydroionone, a tricyclic enol ether and possibly a related lactone. All of these have been reported previously in photoexposures of ambrein made under, arguably, less environmentally-realistic conditions. The latter products were not observed in dark controls however, suggesting they were only products of photo-oxidation.