Free radical oxidation (autoxidation) of α-tocopherol (vitamin E): A potential source of 4, 8, 12, 16-tetramethylheptadecan-4-olide in the environment

The free radical oxidation (autoxidation) of vitamin E has been reinvestigated in order to test whether 4, 8, 12, 16-tetramethylheptadecan-4-olide, a C21 isoprenoid γ-lactone previously detected in various sediments, might derive from such a process. After different laboratory simulations, the production of the lactone via peroxyl radical oxidation of vitamin E has been demonstrated unambiguously and different pathways are proposed to explain its formation. Examination of lipid extracts from photodegraded senescent phytoplanktonic cells demonstrates that autoxidation of vitamin E operated in phytodetritus, affording 4, 8, 12, 16-tetramethylheptadecan-4-olide. Detection of high proportions of the γ-lactone (relative to the parent vitamin E) in different particulate matter samples collected at the DYFAMED time-series station (Ligurian Sea) shows that, as demonstrated in vitro, autoxidation of vitamin E is a rapid process under environmental conditions.