To make one approach to the solusion the relation between a chemical structure and an antioxidant activity, some ε-(3, 4-dihydroxyphenyl) alkanoic esters shown in Table 1 were examined their activities through the Active Oxygen Method.
The said alkanoic estes were synthesized by authors and the fresh lard was used as the substrate which is easy to detect its rancid odor.
The results of the experiment are shown in Table 1 and Figures 1 and 2 and are summarizedas follows:
(1) Et protocatechuate was found to be almost ineffective but a introduction of methylene groups between phenyl and carboalkoxyl groups of protocatechuic ester caused the marked enhancement in activity. The activities of most of all these compounds were proved to be superior to that of ethyl gallate.
(2) Among these compounds, methyl ε-(3, 4-dihydroxyphenyl)-caproate which had 5 methylene groups was the most effective and γ-(3, 4-dihydroxyphenyl)-butyrate having 3 methylene groups the next.
(3) Concerning the alkyl groups of esters, it was found that the order of their activities was Me>Et>
n-Pr, regarding solely to ε-(3, 4-dihydroxyphenyl)-caproic ester. But this should be ascertained by using other alkanoic esters.
(4) It is noteworthy to point out that the protocatechuic ester, which was published by OSHIMA
(7), to be very effective was found to be almost ineffective for the cod liver oil and lard used by authors as the substrates. A discussion on this problem was also described in this paper.
The authors wish to express their appreciation to Professor Dr. Y. SUMIKI for his guidence and advice.
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