Five antioxidative caffeoylquinic acid derivatives were isolated from the roots of burdock (Arctium lappa L.), an edible plant in Japan. Their structures were established as 1-0-,5-O-dicaffeoylquinic acid (1), l-0-,5-0-dicaffeoyl-3-0-succinylquinic acid (2), l-0-,5-0-dicaffeoyl-4-0-succinylquinic acid (3), l-0-,5-0-dicaffeoyl-3-0-,4-0-disuccinylquinic acid (4), and 1-0-,3-0-,5-0-tricaffeoyl-4-0-succinylquinic acid (5) on the basis of chemical and spectral (NMR, MS) evidence. The antioxidant activities were measured in a hexane/2-propanol solution of methyl linoleate in the presence of a radical initiator. The antioxidant efficiency increased in the order of -tocopherol < chlorogenic acid < caffeic acid < (1) = (2) = (3) = (4) < (5).
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