Identification of potent odorants formed by autoxidation of arachidonic acid: Structure elucidation and synthesis of (E,Z,Z)-2,4,7-tridecatrienal

The aroma composition of autoxidized arachidonic acid was characterized by aroma extract dilution analysis. The most potent odorant was trans -4,5-epo xy-(E)-2-decenal followed by 1-octen-3-one, (E,Z)-2,4-decadienal, (E,Z,Z)-2 ,4,7-tridecatrienal, (E,E)-2,4-decadienal, and hexanal. (E,Z,Z)-2,4,7-Tri-d ecatrienal was unequivocally identified by mass spectrometry and nuclear ma gnetic resonance (NMR) data. The stereochemistry of its extended double-bon d system was elucidated on the basis of NMR measurements. The target compou nd was synthesized in four steps starting with bromination of 2-octyn-1-ol, followed by copper-catalyzed coupling of the bromide with ethyl-magnesium bromide and (E)-2-penten-4-yn-1-ol. Partial hydrogenation of the resulting Cia-compound with triple bonds in the positions C-4 and C-7 gave rise to (E ,Z,Z)-2,4,7-tridecatrien-1-ol, which was finally oxidized to the target com pound. It exhibits a typical egg-white-like, marine-like odor at low concen trations, and an intense orange-citrus, animal-like odor at higher concentr ations. Its odor threshold was estimated by gas chromatography-olfactometry to be 0.07 ng/L air, which is of the same order of magnitude as that repor ted for 1-octen-3-one and (E,E)-2,4-decadienal.