Brassicasterol (24-methyl cholest-5,22-dien-3β-ol) is a 28-carbon sterol synthesised by several unicellular algae (phytoplankton) and some terrestrial plants, like rape. This compound has frequently been used as a biomarker for the presence of (marine) algal matter in the environment, and is one of the ingredients in stigmasterol-rich plant sterols (Number E499 in the European numbering system).
There is some evidence to suggest that it may also be a relevant additional biomarker in Alzheimer's disease. More specifically, AD patients have lower levels of this sterol in their cerebrospinal fluid.
Chemical properties Solubility Brassicasterol has a low water solubility and, as a consequence, a high octanol-water partition coefficient. This means that, in most environmental systems, brassicasterol will be associated with the solid phase.
Degradation In anaerobic sediments and soils, brassicasterol is stable for many hundreds of years, enabling it to be used as an indicator of past algal production (see below).
Formation and occurrences It can be found in Mirabilis jalapa.
Algal sources Brassicasterol is formed in plants from the isoprenoid squalene through campesterol as an intermediate. A list of the algae in which brassicasterol has been identified is shown below together with approximate composition.Data from a review by Volkman, 1986
+ Sterol content of selected dinoflagellates (as percentage). Data from Volkman, 1986SpeciesABCDEFGHothers Gonyaulax spp10000000000 Peridinium foliaceum10000000000 Peridinium foliaceum 80200000000 Gonyaulax diegensis390000002932 Pyrocystis lunula76602100015 Gonyaulax polygramma36109700047 Gymnodinium wilczeki263903510000 Glenodinium hallii85000042000 Noctiluca milaris01157306014 Gymnodinium simplex00005300047 Prorocentrum cordatum70005063025
A = cholesterol B = campesterol C = sitosterol D = 22-dehydrocholesterol ((22E)-cholesta-5,22-dien-3β-ol) E = brassicasterol F = stigmasterol G = 24-methylene cholesterol H = fucosterol
Use as a tracer for marine algae The principal source of brassicasterol in the environment is from marine algae. Its relatively high concentration and stability allows it to be used in the assessment of the origin of organic matter in samples, especially sediments.
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