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A mechanistic study to determine and define the antioxidant activity of rosmariquinone
Abstract
The Diels-Alder approach to the synthesis of rosmariquinone (RQ) and RQ derivatives had yields between 35 and 90%. The highest yielding derivatives were those in which an ortho-substituted catechol (eg. 3-isopropyl catechol) was used as a starting material while the lowest yielding were those where no ortho-substitution was present (eg. 4-methyl catechol). Ring A alterations had a slight influence (5 to 10 % loss) in the reaction yield. Antioxidant (AO) activity was also influenced by both ring A and C alterations. Best activity was found in the derivatives containing a carbon-13 (C-13) methyl or hydrogen substitution. The worst activity was found in the unsubstituted A ring (normilitrone). The difference in the activity was associated with the ability of normilitrone to rearrange during the initial oxidation to a C-4/C-5 unsaturated intermediate while RQ, a structure identical to normilitrone except that the C-4 contains two methyl substitutions, can only rearrange to a C-1/C-10 intermediate which is the favored intermediate. Because the C-1/C-10 intermediate was formed in lower amounts, the normilitrone AO activity was also reduced since the C-1/C-10 intermediate was needed to produce-secondary intermediates such as hydroxymilitrone. Hydroxymilitrone was converted in a two step rearrangement process to form the active RQ species, acrucadiol (also labeled miltiodiol). The active species can then act as a hydrogen donor and effectively inhibit the oxidation of stripped soybean oil as well as methyl oleate in photo- and autoxidation. Hydrogen donor activity was also demonstrated by the synergistic activity between RQ and tocopherol. The mechanism is one that RQ, after converting to arucadiol, donates hydrogen to the tocopheroxyl radical formed during the oxidation of the soybean oil. The regeneration of the tocopherol can be explained by the evidence that RQ concentration greatly decreased during the study while maintaining the tocopherol levels. From this study, the RQ antioxidant activity has been elucidated and essential structural features identified.
Subject Area
Organic chemistry|Food science|Biochemistry
Recommended Citation
Hall, Clifford Allen, "A mechanistic study to determine and define the antioxidant activity of rosmariquinone" (1996). ETD collection for University of Nebraska-Lincoln. AAI9720837.
https://digitalcommons.unl.edu/dissertations/AAI9720837