Four Undescribed Chromane-Type Meroterpenoids From Sargassum siliquastrum and Their Inhibitory Activity Against Amyloid-β42 Aggregation.

Four undescribed chromane-type meroterpenoids, sargasilides H-K (1-4), were isolated from the brown alga Sargassum siliquastrum. Their structures were elucidated by comprehensive spectroscopic analyses, and their absolute configurations were partially established by electronic circular dichroism and the modified Mosher's method. The inhibitory effects of 1-4 against amyloid-β42 aggregation were evaluated using a thioflavin T fluorescence assay. Among them, sargasilide J (3) exhibited the strongest activity. Furthermore, compound 3 significantly delayed paralysis in a transgenic Caenorhabditis elegans model expressing amyloid-β42. These findings provide further insight into the structural features governing amyloid-β42 aggregation inhibition in chromane-type meroterpenoids.