Brassicasterol (24-methyl cholest-5,22-dien-3β-ol) is a 28-

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...

sterol Sterol is an organic compound with formula , whose molecule is derived from that of gonane by replacement of a hydrogen atom in position 3 by a hydroxyl group. It is therefore an alcohol of gonane. More generally, any compounds that contain the go ...

synthesised by several

unicellular A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell, unlike a multicellular organism that consists of multiple cells. Organisms fall into two general categories: prokaryotic organisms and ...

algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...

(

phytoplankton Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'. Ph ...

) and some terrestrial plants, like

rape Rape is a type of sexual assault usually involving sexual intercourse or other forms of sexual penetration carried out against a person without their consent. The act may be carried out by physical force, coercion, abuse of authority, or ag ...

. This compound has frequently been used as a biomarker for the presence of (marine) algal matter in the

environment Environment most often refers to: __NOTOC__ * Natural environment, all living and non-living things occurring naturally * Biophysical environment, the physical and biological factors along with their chemical interactions that affect an organism or ...

, and is one of the ingredients for

E number E numbers ("E" stands for "Europe") are codes for substances used as food additives, including those found naturally in many foods such as vitamin C, for use within the European Union (EU) and European Free Trade Association (EFTA). Commonly ...

E499 Stigmasterol-rich plant sterols is a food additive. It is a mixture derived from soybeans that consists of the plant sterols stigmasterol, β-sitosterol, campesterol, and brassicasterol, with stigmasterol representing >85% of the mixture. Its E ...

. There is some evidence to suggest that it may also be a relevant additional biomarker in

Alzheimer's disease Alzheimer's disease (AD) is a neurodegeneration, neurodegenerative disease that usually starts slowly and progressively worsens. It is the cause of 60–70% of cases of dementia. The most common early symptom is difficulty in short-term me ...

Chemical properties

Solubility

Brassicasterol has a low water

solubility In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solubil ...

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).

Chemical analysis

Since the

molecule A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioch ...

has a

hydroxyl In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydroxy ...

(-OH) group, it is frequently bound to other

lipids Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include ...

including

glycerol Glycerol (), also called glycerine in British English and glycerin in American English, is a simple triol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in lipids known ...

s; most analytical methods, therefore, utilise a strong

alkali In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a basic, ionic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a ...

(KOH or NaOH) to

saponify Saponification is a process of converting esters into soaps and alcohols by the action of aqueous alkali (for example, aqueous sodium hydroxide solutions). Soaps are salts of fatty acids, which in turn are carboxylic acids with long carbon chains. ...

the

ester In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ar ...

linkages. Typical extraction

solvents A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for p ...

include 6% KOH in

methanol Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical and the simplest aliphatic alcohol, with the formula C H3 O H (a methyl group linked to a hydroxyl group, often abbreviated as MeOH). It is a ...

. The free

sterols Sterol is an organic compound with formula , whose molecule is derived from that of gonane by replacement of a hydrogen atom in position 3 by a hydroxyl group. It is therefore an alcohol of gonane. More generally, any compounds that contain the gon ...

are then separated from the

polar lipids Polar may refer to: Geography Polar may refer to: * Geographical pole, either of two fixed points on the surface of a rotating body or planet, at 90 degrees from the equator, based on the axis around which a body rotates *Polar climate, the cli ...

by partitioning into a less polar solvent such as

hexane Hexane () is an organic compound, a straight-chain alkane with six carbon atoms and has the molecular formula C6H14. It is a colorless liquid, odorless when pure, and with boiling points approximately . It is widely used as a cheap, relatively ...

. Prior to analysis, the hydroxyl group is frequently derivatised with

BSTFA ''N'',''O''-Bis(trimethylsilyl)trifluoroacetamide (BSTFA) is a chemical compound that is used to derivatise labile groups such as hydroxyl on other chemicals, with the more stable trimethylsilyl group, which protects the labile group and allows th ...

(bis-trimethyl silyl trifluoroacetamide) to replace the hydrogen with the less exchangeable

trimethylsilyl A trimethylsilyl group (abbreviated TMS) is a functional group in organic chemistry. This group consists of three methyl groups bonded to a silicon atom minus;Si(CH3)3 which is in turn bonded to the rest of a molecule. This structural group is ch ...

(TMS) group. Instrumental analysis is frequently conducted on

gas chromatograph Gas chromatography (GC) is a common type of chromatography used in analytical chemistry for separating and analyzing compounds that can be vaporized without decomposition. Typical uses of GC include testing the purity of a particular substance, ...

(GC) with either a flame ionisation detector (FID) or mass spectrometer (MS). The mass spectrum for the TMS ether of brassicasterol can be seen in the figure.

Formation and occurrences

It can be found in '' Mirabilis jalapa''.

Algal sources

Brassicasterol is formed in plants from the

isoprenoid The terpenoids, also known as isoprenoids, are a class of naturally occurring organic chemicals derived from the 5-carbon compound isoprene and its derivatives called terpenes, diterpenes, etc. While sometimes used interchangeably with "terpenes", ...

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 :A =

cholesterol Cholesterol is any of a class of certain organic molecules called lipids. It is a sterol (or modified steroid), a type of lipid. Cholesterol is biosynthesized by all animal cells and is an essential structural component of animal cell mem ...

:B = campesterol :C =

sitosterol β-sitosterol (beta-sitosterol) is one of several phytosterols (plant sterols) with chemical structures similar to that of cholesterol. It is a white, waxy powder with a characteristic odor, and is one of the components of the food additive E499. ...

:D = 22-dehydrocholesterol ((22''E'')-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.

Brassicasterol / cholesterol ratio

The concentration of brassicasterol in a core sample from

Loch Striven Loch Striven ( gd, Loch Sroigheann) is a sea loch extending off the Firth of Clyde, and forms part of the Cowal peninsula coast, in Argyll and Bute, Scotland. Loch Striven extends off of the Firth of Clyde just north of the Isle of Bute, where ...

Scotland Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to the ...

. Highest values may be seen in the top sections of the sediment, which decrease with depth. However, the cholesterol behaves in a similar manner, and the ratio brassicasterol/cholesterol is fairly uniform at all depths, indicating either a comparable degradation rate with no change in source or different degradation rates and a change in source.

Multivariate analysis

Multivariate statistical analyses Multivariate may refer to: In mathematics * Multivariable calculus * Multivariate function * Polynomial#Number of variables, Multivariate polynomial In computing * Multivariate cryptography * Multivariate division algorithm * Multivariate interp ...

such as

principal component analysis Principal component analysis (PCA) is a popular technique for analyzing large datasets containing a high number of dimensions/features per observation, increasing the interpretability of data while preserving the maximum amount of information, and ...

of a range of

lipid Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include ...

biomarkers (''e.g.'', other sterols,

fatty acid In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, fr ...

s, and

fatty alcohols Fatty alcohols (or long-chain alcohols) are usually high-molecular-weight, straight-chain primary alcohols, but can also range from as few as 4–6 carbons to as many as 22–26, derived from natural fats and oils. The precise chain length varies ...

) enable identification of compounds that have similar origins or behaviour. An example can be seen in the loadings plot for sediment samples from the

Mawddach The Afon Mawddach ( en, River Mawddach, italic=yes) is a river in Gwynedd, Wales, which has its source in a wide area north of Dduallt in Snowdonia. It is 28 miles (45 km) in length, and is much branched; many of the significant tributa ...

Estuary,

Wales Wales ( cy, Cymru ) is a Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by England to the Wales–England border, east, the Irish Sea to the north and west, the Celtic Sea to the south west and the ...

.
The location of brassicasterol in this figure (shown in red) indicates that the distribution of this compound is similar to that of the short-chain fatty acids and alcohols, which are known to be of marine origin. The terrestrially derived biomarkers such as β-sitosterol are on the opposite side of the figure and are mutually exclusive.

References

{{Cholesterol metabolism intermediates Cholestanes Phytosterols