Radical scavenging activity of dicaffeoyloxycyclohexanes: contribution of an intramolecular interaction of two caffeoyl residues.
Six regio- and stereoisomers of dicaffeoyloxycyclohexanes and 2,4-di-O-caffeoyl-1,6-anhydro-beta-D-glucose were synthesized as model compounds of dicaffeoylquinic acids, and their radical scavenging activity was evaluated by DPPH (2,2-diphenyl-1-picrylhydrazyl) and ABTS (2,2'-azinobis(3-ethylbenzthiazoline-6-sulfonic acid) diammonium salt) radical scavenging tests. Both DPPH and ABTS radical scavenging reactions of these compounds consisted of two different steps. In the first step, catechol moieties of the caffeoyl residues were rapidly converted to o-quinone structures and no significant difference in the reactivity was observed among the tested compounds. In the second step, however, the rate of the reaction increased as the intramolecular distance of the two caffeoyl residues decreased. A novel intramolecular coupling product, which could scavenge additional radicals, was isolated from the reaction mixture of trans-1,2-dicaffeoyloxycyclohexane and DPPH radical. The result suggests that the second step of the radical scavenging reaction is arising from an intramolecular interaction between the two caffeoquinone residues to regenerate catechol structures, and that the closer their distance is, the more rapidly they react. The radical scavenging activity of natural dicaffeoylquinic acids in a biological aqueous system might also depend on the positions of caffeoyl ester groups.
Saito
Shizuka
S
Laboratory of Food Biochemistry, Division of Applied Bioscience, Graduate School of Agriculture, Hokkaido University, Kita-ku, Sapporo 060-8589, Japan.
Kurakane
Satoshi
S
Seki
Miyuki
M
Takai
Eiji
E
Kasai
Takanori
T
Kawabata
Jun
J
D052160:Benzothiazoles; D001713:Biphenyl Compounds; D002109:Caffeic Acids / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D003510:Cyclohexanes / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D016166:Free Radical Scavengers / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D007202:Indicators and Reagents / Q000737:chemistry; D015394:Molecular Structure; D010851:Picrates / Q000737:chemistry; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D013451:Sulfonic Acids / Q000737:chemistry
D052160:Benzothiazoles; D001713:Biphenyl Compounds; D002109:Caffeic Acids; D003510:Cyclohexanes; D016166:Free Radical Scavengers; D007202:Indicators and Reagents; D010851:Picrates; D013451:Sulfonic Acids; C002502:2,2'-azino-di-(3-ethylbenzothiazoline)-6-sulfonic acid; C004931:1,1-diphenyl-2-picrylhydrazyl