(3R,4aR,5S,6R)-6-Hydroxy-5-methylramulosin (1) was isolated from a culture of a sterile mycelium, which was derived from the green alga, Codium fragile, along with (−)-5-methylmellein (2), (−)-5-hydroxymethylmellein (3), and (−)-(3R,4R)-cis-4-hydroxy-5-methylmellein (4). The absolute configuration of 1 was determined by the NMR data along with the lactone sector rule by circular dichroism (CD). Compound 1 exhibited moderate cytotoxic activity against HeLa cells.
