Antioxidant and Anti-inflammatory Meroterpenoids from the Brown Alga <i>Cystoseira usneoides</i>

A chemical study of the alga <i>Cystoseira usneoides</i> has led to the isolation of six new meroterpenoids, cystodiones A–F (<b>1</b>–<b>6</b>), together with six known related compounds (<b>7</b>–<b>12</b>). The structures of the new metabolites have been established by spectroscopic techniques. In antioxidant assays all of the tested meroterpenes, and in particular cystodiones A (<b>1</b>) and B (<b>2</b>), 6-<i>cis</i>-amentadione-1′-methyl ether (<b>7</b>), and amentadione-1′-methyl ether (<b>8</b>), exhibited strong radical-scavenging activity. In anti-inflammatory assays, usneoidone Z (<b>11</b>) and its corresponding 6<i>E</i> isomer (<b>12</b>) showed significant activity as inhibitors of the production of the proinflammatory cytokine TNF-α in LPS-stimulated THP-1 human macrophages.