Synthesis and Antioxidant Activity of Rosmariquinone and Several Analogues

Rosmariquinone (1) and six analogues were chemically synthesized using an ultrasound-promoted Diels−Alder cycloaddition in yields of 35−90%. The analogues included substitution of the isopropyl at carbon 13 (C-13) with a hydrogen (5), methyl (6), or tert-butyl (4) substituent. The hydrogen-substitut...

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Bibliographic Details
Published in:Journal of agricultural and food chemistry 1998-04, Vol.46 (4), p.1303-1310
Main Authors: Hall, Clifford A, Cuppett, Susan L, Dussault, Pat
Format: Article
Language:English
Subjects:
ANTIOXIDANTS
CHEMICAL STRUCTURE
Chemistry
Condensed benzenic and aromatic compounds
DIELS-ALDER CYCLOADDITION
Exact sciences and technology
NATURAL ANTIOXIDANTS
Organic chemistry
OXIDATION
Preparations and properties
QUINONES
SOYBEAN OIL
SPECTRAL ANALYSIS
SPECTRAL DATA
SPECTROMETRY
STRUCTURE ACTIVITY RELATIONSHIPS
ULTRASONICS
YIELDS
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Summary:Rosmariquinone (1) and six analogues were chemically synthesized using an ultrasound-promoted Diels−Alder cycloaddition in yields of 35−90%. The analogues included substitution of the isopropyl at carbon 13 (C-13) with a hydrogen (5), methyl (6), or tert-butyl (4) substituent. The hydrogen-substituted analogue had the lowest yield at 35%, due in part to the instability of the compound to air, while the highest yields were achieved for the methyl (85%) and tert-butyl (90%) analogues. The 60% yield obtained for the C-14 methyl analogue (7; no C-13 isopropyl) may have been caused by the meta-substituted catechol inhibiting the cycloaddition. The final two analogues were ring A modifications and included the removal of one C-4 methyl (3; 80% yield) or both C-4 methyl (2; 85% yield) groups. The analogues were tested against rosmariquinone in light-sensitized oxidation of stripped soybean oil. Analogues 5 and 6 were significantly (P < 0.05) better antioxidants than rosmariquinone and all other analogues. The antioxidant properties of compounds 2−7 were not significantly different (P < 0.05) from each other while compounds 2 and 4 had significantly (P < 0.05) lower antioxidant activity than rosmariquinone. This study demonstrated the importance of structural characteristics of antioxidants and that natural antioxidants, such as rosmariquinone, can be improved through chemical modification. Keywords: Antioxidant activity; Diels−Alder cycloaddition; rosmariquinone; ultrasound
ISSN:0021-8561
1520-5118
DOI:10.1021/jf970742k