“Dinoflagellate Sterols” in marine diatoms

► NMR spectrometry confirmed that some diatoms contain 23-methyl sterols. ► 27-Norsterol occelasterol was found in a diatom. ► A sterol with an hitherto unknown side chain, stigmasta-5,24,28-trienol, was isolated and synthesized. ► A previously undescribed sterol, 23-methylcholesta-7,22-dienol, was isolated.