Sterol composition of the Black Sea Hydrozoan, Obelia longissima (Pallas 1766)

Abstract

This is the first investigation on the steroids of the hydrozoan genus Obelia. Thirty known sterols were identified, 20 of them were 4-desmethyl sterols, four coprostanols, and six 4-methyl sterols. For two other sterols that appear to be new sterols, tentative structures 13d and 14b are proposed on the basis of the mass spectral fragmentation. Contrary to other Hydrozoans, Obelia longissima contains a very complex sterol mixture, cholesterol not being the main sterol. The main sterol appears to be the (22Z)-isomer of brassicasterol 16a (probably a mixture of two C-24 epimers). The only other (22Z)–sterol seems to be 17a. Sitosterol appears to be a 24β isomer (clionasterol). Sterol esters possess a sterol composition different from that of the free sterols.