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Abstract
Methyleugenol, the methyl ether of eugenol, both of which are flavorant constituents of spices, has been listed by the National Toxicology Program’s Report on Carcinogens as reasonably anticipated to be a human carcinogen. This finding is based on the observation of increased incidence of malignant tumors at multiple tissue sites in experimental animals of different species. By contrast, eugenol is not listed. In this study, we show that both methyleugenol and eugenol readily undergo peroxidative metabolism in vitro to form free radicals with large hyperfine interactions of the methylene allylic hydrogen atoms. These large hyperfine splittings indicate large electron densities adjacent to those hydrogen atoms. Methyleugenol undergoes autoxidation such that the commercial product contains 10–30 mg/L hydroperoxide and is capable of activating peroxidases without the presence of added hydrogen peroxide. Additionally, the hydroperoxide is not a good substrate for catalase, which demonstrates that these antioxidant defenses will not be effective in protecting against methyleugenol exposure.
Highlights
Methyleugenol (Chart 1A, CAS # 93-15-2) is the methyl ether of eugenol (Chart1B, CAS # 97-53-0), which is itself a majorChart 1
MEU oxidized by HRP activated by hydrogen peroxide in a fastflow system produced a well-resolved electron paramagnetic resonance spectroscopy (EPR) spectrum of the corresponding radical cation (Figure 1A)
When hydrogen peroxide was omitted, a strong EPR signal was still observed (Figure 2D), and the same spectrum was observed in the presence of catalase at a concentration 70 times that of the peroxidase (Figure 2E)
Summary
Methyleugenol (Chart 1A, CAS # 93-15-2) is the methyl ether of eugenol (Chart1B, CAS # 97-53-0), which is itself a majorChart 1. Constituent of spices such as clove, allspice, and bay leaves[1] and is known to induce contact allergies.[2,3] Methyleugenol (MEU) and eugenol (EUG) are allylalkoxybenzene derivatives that are present as flavoring constituents in foodstuffs or are added as flavor extenders. Their chemical structures resemble those of safrole, a known carcinogen, and estragole.[4] A safety assessment of allylalkoxybenzene derivatives was prepared by the Expert Panel of the Flavor and Extract Manufacturers’ Association, which summarized previous findings about the safety of MEU. They conclude that the present human exposure to MEU does not pose a significant cancer risk.[5]
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