Muriceanol, a 24(28)-Epoxide Sterol Link in the Carbon Flux Toward Side-Chain Dealkylation of Sterols

Side‐chain‐oxidized C‐28‐sterol 1 and one new pregnane metabolite 2 were isolated from eastern Pacific Muricea spp. The C‐24(28)‐epoxide functionality is a key intermediate in the C‐24‐dealkylation mechanism of the conversion of phytosterol to cholesterol by phytophagous insects. Certain marine invertebrates share this dealkylation pathway; however, such a key epoxide feature has not yet been found in a naturally occurring sterol from marine invertebrates. The unusual oxidation pattern of the side chain of 1 encourages speculation about its biogenesis and converts this non‐zooxanthellate gorgonia into an interesting candidate organism for biosynthetic studies on C‐24‐dealkylation of phytosterols in octocorals. The (22S)‐22‐hydroxy group, after 24‐dealkylation of 1, may be an advantageous functionalization in the side‐chain cleavage to C‐21‐pregnane steroids in Muricea spp. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)