Antibiotics from Algae. XXXV. Phlorotannins from Ecklonia maxima1

New phloroglucinol derivatives were isolated from the ethanolic extract of ECKLONIA MAXIMA, a brown alga found off the west coast of South Africa. Most of these compounds contain dibenzo[1,4]dioxin elements. The common basic unit of all the compounds found is eckol, a hexahydroxyphenoxydibenzo[1,4]dioxin composed of 3 phloroglucinol units. Phloroeckol A and B represent four-ringed phloroglucinol derivatives, whereas the only five-ringed substance (furodehydroeckol) displays a furan structure in addition. Six-ringed phloroglucinol derivatives composed of two eckol units joined either symmetrically (such as 7,7'-bieckol, 9,9'-bieckol) or asymmetrically (7,9'-bieckol, dieckol) are found frequently. Apart from these, tetraphlorethol C, a four-ringed tetraphloroglucinol triether which lacks both dioxin and furan structures, also occurs.