Structure of an anti-plasmin inhibitor, eckol, isolated from the brown alga Ecklonia kurome Okamura and inhibitory activities of its derivatives on plasma plasmin inhibitors.

Eckol (1), a novel phlorotannin with a dibenzo-1, 4-dioxin skeleton, has been isolated from the brown alga Ecklonia kurome OKAMURA as a potent and specifif and specific anti-plasmin inhibitor. Its structure has been elucidated based on the spectral data, in particular, by means of negative nuclear Overhauser effect (NOE), and finally established as 1-(3, 5-dihydroxyphenoxy)-2, 4, 7, 9-tetrahydroxydibenzo-1, 4-dioxin by X-ray analysis. Some partially methoxylated derivatives of eckol wre prepared by methylation with diazomethane and also by selective demethylation of eckol permethylate (1b) to establish the structural requirements for inhibitory activities on α2-macroglobulin and α2-plasmin inhibitor, the main plasmin inhibitors in plasma.