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.

1. A = cholesterol

2. B = campesterol

3. C = sitosterol

4. D = 22-dehydrocholesterol ((22E)-cholesta-5,22-dien-3β-ol)

5. E = brassicasterol

6. F = stigmasterol

7. G = 24-methylene cholesterol

8. 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.

References