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, a prototypical steroid with 32 carbon atoms. Its core ring system (ABCD), composed of 17 carbon atoms, is shown with IUPAC-approved ring lettering and atom numbering.]]A steroid is an organic compound with four fused compound rings (designated A, B, C, and D) arranged in a specific molecular configuration.
Steroids have two principal biological functions: as important components of that alter membrane fluidity; and as signaling molecules. Examples include the lipid cholesterol, sex hormones estradiol and testosterone, (2025). 9780470660843, Wiley. ISBN 9780470660843 , and the anti-inflammatory corticosteroid drug dexamethasone. Hundreds of steroids are found in Fungus, , and . All steroids are manufactured in cells from a sterols: cholesterol (animals), lanosterol (opisthokonts), or cycloartenol (plants). All three of these molecules are produced via Cyclic compound of the triterpene squalene.
Gonane, also known as steran or cyclopentanoperhydrophenanthrene, the nucleus of all steroids and sterols, (1991). 9780849364150, CRC Press. ISBN 9780849364150 (1994). 9783540574200, Springer Science & Business Media. ISBN 9783540574200 is composed of seventeen carbon atoms in carbon-carbon bonds forming four fused compound in a three-dimensional shape. The three cyclohexane rings (A, B, and C in the first illustration) form the skeleton of a hydrogenation derivative of phenanthrene. The D ring has a cyclopentane structure. When the two methyl groups and eight carbon (at C-17, as shown for cholesterol) are present, the steroid is said to have a cholestane framework. The two common 5α and 5β stereoisomeric forms of steroids exist because of differences in the side of the largely planar ring system where the hydrogen (H) atom at carbon-5 is attached, which results in a change in steroid A-ring conformation. Isomerisation at the C-21 side chain produces a parallel series of compounds, referred to as isosteroids.
Examples of steroid structures are:
| , a prototype animal sterol. This structural lipid and key steroid biosynthesis precursor.]] | , a common steroid core]] |
The letters α and β denote absolute stereochemistry at Stereocenter—a specific nomenclature distinct from the R/S convention
The name "11-deoxycortisol" is an example of a derived name that uses cortisol as a parent structure without an oxygen atom (hence "deoxy") attached to position 11 (as a part of a hydroxy group).
Unsaturated carbons (generally, ones that are part of a double bond) in the steroid nucleus are indicated by changing -ane to -ene. This change was traditionally done in the parent name, adding a prefix to denote the position, with or without Δ (Greek capital delta) which designates unsaturation, for example, 4-pregnene-11β,17α-diol-3,20-dione (also Δ4-pregnene-11β,17α-diol-3,20-dione) or 4-androstene-3,11,17-trione (also Δ4-androstene-3,11,17-trione). However, the Nomenclature of Steroids recommends the locant of a double bond to be always adjacent to the syllable designating the unsaturation, therefore, having it as a suffix rather than a prefix, and without the use of the Δ character, i.e. pregn-4-ene-11β,17α-diol-3,20-dione or androst-4-ene-3,11,17-trione. The double bond is designated by the lower-numbered carbon atom, i.e. "Δ4-" or "4-ene" means the double bond between positions 4 and 5. The saturation of carbons of a parent steroid can be done by adding "dihydro-" prefix,
The abbreviations like "Progesterone" for progesterone and "Androstenedione" for androstenedione for refer to Δ4-steroids, while "Pregnenolone" for pregnenolone and "Androstenediol" for androstenediol refer to Δ5-steroids.
The suffix -ol denotes a hydroxy group, while the suffix -one denotes an oxo group. When two or three identical groups are attached to the base structure at different positions, the suffix is indicated as -diol or -triol for hydroxy, and -dione or -trione for oxo groups, respectively. For example, 5α-pregnane-3α,17α-diol-20-one has a hydrogen atom at the 5α position (hence the "5α-" prefix), two hydroxy groups (-OH) at the 3α and 17α positions (hence "3α,17α-diol" suffix) and an oxo group (=O) at the position 20 (hence the "20-one" suffix). However, erroneous use of suffixes can be found, e.g., "5α-pregnan-17α-diol-3,11,20-trione" sic — since it has just one hydroxy group (at 17α) rather than two, then the suffix should be -ol, rather than -diol, so that the correct name to be "5α-pregnan-17α-ol-3,11,20-trione".
According to the rule set in the Nomenclature of Steroids, the terminal "e" in the parent structure name should be elided before the vowel (the presence or absence of a number does not affect such elision). This means, for instance, that if the suffix immediately appended to the parent structure name begins with a vowel, the trailing "e" is removed from that name. An example of such removal is "5α-pregnan-17α-ol-3,20-dione", where the last "e" of "pregnane" is dropped due to the vowel ("o") at the beginning of the suffix -ol. Some authors incorrectly use this rule, eliding the terminal "e" where it should be kept, or vice versa.
The term "11-oxygenated" refers to the presence of an oxygen atom as an oxo (=O) or hydroxy (-OH) substituent at carbon 11. "Oxygenated" is consistently used within the chemistry of the steroids since the 1950s. Some studies use the term "11-oxyandrogens" as an abbreviation for 11-oxygenated androgens, to emphasize that they all have an oxygen atom attached to carbon at position 11. However, in chemical nomenclature, the prefix "oxy" is associated with ether functional groups, i.e., a compound with an oxygen atom connected to two Alkyl group or Aryl group groups (R-O-R),
Even though "keto" is a standard prefix in organic chemistry, the 1989 recommendations of the Joint Commission on Biochemical Nomenclature discourage the application of the prefix "keto" for steroid names, and favor the prefix "oxo" (e.g., 11-oxo steroids rather than 11-keto steroids), because "keto" includes the carbon that is part of the steroid nucleus and the same carbon atom should not be specified twice.
During eukaryogenesis—the evolutionary process that gave rise to modern eukaryotic cells—steroids likely facilitated the endosymbiotic acquisition of mitochondria.
Prokaryotic sterol synthesis involves the tetracyclic steroid framework, as found in myxobacteria, as well as hopanoids, pentacyclic lipids that regulate bacterial membrane functions. These sterol biosynthetic pathways may have originated in bacteria or been transferred from .
Sterol synthesis depends on two key enzymes: squalene monooxygenase and oxidosqualene cyclase. Phylogenetic analyses of oxidosqualene cyclase (Osc) suggest that some bacterial Osc genes may have been acquired via horizontal gene transfer from eukaryotes, as certain bacterial Osc proteins closely resemble their eukaryotic homologs.
Ergosterol is analogous to the cholesterol found in the cellular membranes of animals (including humans), or the phytosterols found in the cellular membranes of plants.
Ergosterol is responsible for the vitamin D content found in mushrooms; ergosterol is chemically converted into provitamin D2 by exposure to ultraviolet light. Provitamin D2 spontaneously forms vitamin D2. However, not all fungi utilize ergosterol in their cellular membranes; for example, the pathogenic fungal species Pneumocystis jirovecii does not, which has important clinical implications (given the mechanism of action of many antifungal drugs). Using the fungus Saccharomyces cerevisiae as an example, other major steroids include ergosta‐5,7,22,24(28)‐tetraen‐3β‐ol, zymosterol, and lanosterol. S. cerevisiae utilizes 5,6‐dihydroergosterol in place of ergosterol in its cell membrane.
Additional classes of steroids include:
As well as the following class of (open-ring steroids):
The gonane (steroid nucleus) is the parent 17-carbon tetracyclic hydrocarbon molecule with no alkyl sidechains.
(nor-, L. norma; "normal" in chemistry, indicating carbon removal) and homosteroids (homo-, Greek homos; "same", indicating carbon addition) are structural subclasses of steroids formed from biosynthetic steps. The former involves enzymic ring expansion reactions, and the latter is accomplished (biomimetically) or (more frequently) through of acyclic precursors with more (or fewer) ring atoms than the parent steroid framework.
Combinations of these ring alterations are known in nature. For instance, Sheep who graze on Veratrum ingest cyclopamine (shown) and veratramine, two of a sub-family of steroids where the C- and D-rings are contracted and expanded respectively via a biosynthesis migration of the original C-13 atom. Ingestion of these C-nor-D-homosteroids results in birth defects in lambs: cyclopia from cyclopamine and leg deformity from veratramine.
Steroids play critical roles in a number of disorders, including malignancies like prostate cancer, where steroid production inside and outside the tumour promotes cancer cell aggressiveness.
Steroid biosynthesis is an anabolism pathway which produces steroids from simple precursors. A unique biosynthetic pathway is followed in animals (compared to many other ), making the pathway a common target for and other anti-infection drugs. Steroid metabolism in humans is also the target of cholesterol-lowering drugs, such as . In humans and other animals the biosynthesis of steroids follows the mevalonate pathway, which uses acetyl-CoA as building blocks for dimethylallyl diphosphate (DMAPP) and isopentenyl diphosphate (IPP).
In subsequent steps DMAPP and IPP conjugate to form farnesyl diphosphate (FPP), which further conjugates with each other to form the linear triterpenoid squalene. Squalene biosynthesis is catalyzed by squalene synthase, which belongs to the squalene/phytoene synthase family. Subsequent Epoxide and cyclization of squalene generate lanosterol, which is the starting point for additional modifications into other steroids (steroidogenesis). In other eukaryotes, the cyclization product of epoxidized squalene (oxidosqualene) is cycloartenol.
DMAPP and IPP donate isoprene units, which are assembled and modified to form and terpenoid (a large class of lipids, which include the and form the largest class of plant ). Here, the activated isoprene units are joined to make squalene and folded into a set of rings to make lanosterol. Lanosterol can then be converted into other steroids, such as cholesterol and ergosterol.
Two classes of medication target the mevalonate pathway: (like rosuvastatin), which are used to reduce elevated cholesterol levels, and (like zoledronate), which are used to treat a number of bone-degenerative diseases.
During diseases pathways otherwise not significant in healthy humans can become utilized. For example, in one form of congenital adrenal hyperplasia a deficiency in the 21-hydroxylase enzymatic pathway leads to an excess of 17α-Hydroxyprogesterone (17-OHP) – this pathological excess of 17-OHP in turn may be converted to dihydrotestosterone (DHT, a potent androgen) through among others 17,20 Lyase (a member of the cytochrome P450 family of enzymes), 5α-Reductase and 3α-Hydroxysteroid dehydrogenase.
The methods of isolation to achieve the two scales of product are distinct, but include extraction, precipitation, adsorption, chromatography, and crystallization. In both cases, the isolated substance is purified to chemical homogeneity; combined separation and analytical methods, such as LC-MS, are chosen to be "orthogonal"—achieving their separations based on distinct modes of interaction between substance and isolating matrix—to detect a single species in the pure sample.
Structure determination refers to the methods to determine the chemical structure of an isolated pure steroid, using an evolving array of chemical and physical methods which have included NMR and small-molecule crystallography. Methods of analysis overlap both of the above areas, emphasizing analytical methods to determining if a steroid is present in a mixture and determining its quantity.
(2025). 9780854041824, The Royal Society of Chemistry. ISBN 9780854041824 of organic chemistry to denote absolute configuration of functional groups, known as Cahn–Ingold–Prelog priority rules. The R/S convention assigns priorities to substituents on a chiral center based on their atomic number. The highest priority group is assigned to the atom with the highest atomic number, and the lowest priority group is assigned to the atom with the lowest atomic number. The molecule is then oriented so that the lowest priority group points away from the viewer, and the remaining three groups are arranged in order of decreasing priority around the chiral center. If this arrangement is clockwise, it is assigned an R configuration; if it is counterclockwise, it is assigned an S configuration. In contrast, steroid nomenclature uses α and β to denote stereochemistry at chiral centers. The α and β designations are based on the orientation of substituents relative to each other in a specific ring system. In general, α refers to a substituent that is oriented towards the plane of the ring system, while β refers to a substituent that is oriented away from the plane of the ring system. In steroids drawn from the standard perspective used in this paper, α-bonds are depicted on figures as dashed wedges and β-bonds as solid wedges.
(2025). 9780854041824, The Royal Society of Chemistry. ISBN 9780854041824 The numbering of positions of carbon atoms in the steroid nucleus is set in a template found in the Nomenclature of Steroids that is used regardless of whether an atom is present in the steroid in question.
(2025). 9780854041824, The Royal Society of Chemistry. ISBN 9780854041824 i.e., a saturation of carbons 4 and 5 of testosterone with two hydrogen atoms is 4,5α-dihydrotestosterone or 4,5β-dihydrotestosterone. Generally, when there is no ambiguity, one number of a hydrogen position from a steroid with a saturated bond may be omitted, leaving only the position of the second hydrogen atom, e.g., 5α-dihydrotestosterone or 5β-dihydrotestosterone. The Δ5-steroids are those with a double bond between carbons 5 and 6 and the Δ4 steroids are those with a double bond between carbons 4 and 5.
(2025). 9780854041824, The Royal Society of Chemistry. ISBN 9780854041824 therefore, using "oxy" within the name of a steroid class may be misleading. One can find clear examples of "oxygenated" to refer to a broad class of organic molecules containing a variety of oxygen containing functional groups in other domains of organic chemistry, and it is appropriate to use this convention.
Species distribution
Steroids are present across all domains of life, including bacteria, archaea, and . In eukaryotes, steroids are particularly abundant in fungi, plants, and animals.
Eukaryotic
Eukaryote cells, encompassing animals, plants, fungi, and protists, are characterized by their complex cellular structures, including a true nucleus and membrane-bound organelles. Sterols, a subgroup of steroids, play crucial roles in maintaining membrane fluidity, supporting cell signaling, and enhancing stress tolerance. These compounds are integral to eukaryotic membranes, where they contribute to membrane integrity and functionality.
Prokaryotic
Although sterol biosynthesis is rare in prokaryotes, certain bacteria, including Methylococcus capsulatus, specific , myxobacteria, and the planctomycete Gemmata obscuriglobus, are capable of producing sterols. In G. obscuriglobus, sterols are essential for cell viability, but their roles in other bacteria remain poorly understood. (2025). 9783030775957, Springer. ISBN 9783030775957
Fungal
Fungal steroids include the , which are involved in maintaining the integrity of the fungal cellular membrane. Various antifungal drugs, such as amphotericin B and azole antifungals, utilize this information to kill pathogenic fungi. (2017). 9783319486833, Springer. ISBN 9783319486833 Fungi can alter their ergosterol content (e.g. through loss of function mutations in the enzymes ERG3 or ERG6, inducing depletion of ergosterol, or mutations that decrease the ergosterol content) to develop resistance to drugs that target ergosterol.
(2017). 9781119374312, John Wiley & Sons, Inc.. ISBN 9781119374312 All mushrooms contain large quantities of ergosterol, in the range of tens to hundreds of milligrams per 100 grams of dry weight. Oxygen is necessary for the synthesis of ergosterol in fungi.
Plant
Plant steroids include steroidal found in Solanaceae and Melanthiaceae (specially the genus Veratrum), (2025). 9780881929522, Timber press inc.. ISBN 9780881929522 cardiac glycosides, (2025). 9780881929522, Timber press inc.. ISBN 9780881929522 the and the (which include several plant hormones).
Animal
Animal steroids include compounds of vertebrate and insect origin, the latter including such as ecdysterone (controlling molting in some species). Vertebrate examples include the steroid hormones and cholesterol; the latter is a structural component of cell membranes that helps determine the fluidity of cell membranes and is a principal constituent of Atheroma (implicated in atherosclerosis). Steroid hormones include:
Types
By function
The major classes of steroid hormones, with prominent members and examples of related functions, are:
By structure
Intact ring system
Steroids can be classified based on their chemical composition. (2025). 9781440802997, Greenwood Press. ISBN 9781440802997 One example of how MeSH performs this classification is available at the Wikipedia MeSH catalog. Examples of this classification include:
In biology, it is common to name the above steroid classes by the number of carbon atoms present when referring to hormones: C18-steroids for the estranes (mostly estrogens), C19-steroids for the androstanes (mostly androgens), and C21-steroids for the pregnanes (mostly corticosteroids). The classification "17-ketosteroid" is also important in medicine.
Cholesterol 27 Cholic acid 24 Progesterone 21 Testosterone 19 Estradiol 18
Cleaved, contracted, and expanded rings
Secosteroids (Latin seco, "to cut") are a subclass of steroidal compounds resulting, Biosynthesis or conceptually, from scission (cleavage) of parent steroid rings (generally one of the four). Major secosteroid subclasses are defined by the steroid carbon atoms where this scission has taken place. For instance, the prototypical secosteroid cholecalciferol, vitamin D3 (shown), is in the 9,10-secosteroid subclass and derives from the cleavage of carbon atoms C-9 and C-10 of the steroid B-ring; 5,6-secosteroids and 13,14-steroids are similar.
(2025). 9783642340642, Springer. ISBN 9783642340642 A further C-nor-D-homosteroid (nakiterpiosin) is excreted by Okinawan cyanobacteria. e.g., Terpios hoshinota, leading to coral mortality from black coral disease. Nakiterpiosin-type steroids are active against the signaling pathway involving the smoothened and hedgehog proteins, a pathway which is hyperactive in a number of cancers.
Biological significance
Steroids and their metabolites often function as signalling molecules (the most notable examples are steroid hormones), and steroids and are components of . (2025). 9780321981226, Sinauer Associates; W.H. Freeman & Co.. ISBN 9780321981226 Steroids such as cholesterol decrease membrane fluidity. (2025). 9781429246460, Freeman. ISBN 9781429246460
Similar to , steroids are highly concentrated energy stores. However, they are not typically sources of energy; in mammals, they are normally metabolized and excreted.
Biosynthesis and metabolism
The hundreds of steroids found in animals, fungi, and are made from lanosterol (in animals and fungi; see examples above) or cycloartenol (in other eukaryotes). Both lanosterol and cycloartenol derive from Cyclic compound of the triterpene squalene. Lanosterol and cycloartenol are sometimes called protosterols because they serve as the starting compounds for all other steroids.
Mevalonate pathway
The mevalonate pathway (also called HMG-CoA reductase pathway) begins with acetyl-CoA and ends with dimethylallyl diphosphate (DMAPP) and isopentenyl diphosphate (IPP).
Steroidogenesis
Steroidogenesis is the biological process by which steroids are generated from cholesterol and changed into other steroids. The pathways of steroidogenesis differ among species. The major classes of steroid hormones, as noted above (with their prominent members and functions), are the , (corticoids), , and . Human steroidogenesis of these classes occurs in a number of locations:
(2025). 9783319445571 ISBN 9783319445571 (some testosterone may also be produced in the adrenal cortex).
Alternative pathways
In plants and bacteria, the non-mevalonate pathway (MEP pathway) uses Pyruvic acid and glyceraldehyde 3-phosphate as substrates to produce IPP and DMAPP.
Catabolism and excretion
Steroids are primarily oxidized by cytochrome P450 oxidase enzymes, such as CYP3A4. These reactions introduce oxygen into the steroid ring, allowing the cholesterol to be broken up by other enzymes into bile acids. These acids can then be eliminated by secretion from the liver in bile. The expression of the oxidase gene can be upregulated by the steroid sensor PXR when there is a high blood concentration of steroids. Steroid hormones, lacking the side chain of cholesterol and bile acids, are typically Hydroxylation at various ring positions or oxidized at the 17 position, conjugated with sulfate or glucuronic acid and excreted in the urine.
Isolation, structure determination, and methods of analysis
Steroid isolation, depending on context, is the isolation of chemical matter required for chemical structure elucidation, derivitzation or degradation chemistry, biological testing, and other research needs (generally milligrams to grams, but often more or the isolation of "analytical quantities" of the substance of interest (where the focus is on identifying and quantifying the substance (for example, in biological tissue or fluid). The amount isolated depends on the analytical method, but is generally less than one microgram. (2025). 9781402097744, Springer. ISBN 9781402097744
Chemical synthesis
Microbial catabolism of phytosterol yields C-19 steroids, C-22 steroids, and 17-ketosteroids (i.e. precursors to adrenocortical hormones and ). (2025). 9783527306732, Wiley-VCH Verlag GmbH & Co. KGaA. ISBN 9783527306732 The addition and modification of is key when producing the wide variety of medications available within this chemical classification. These modifications are performed using conventional organic synthesis and/or biotransformation techniques. (1966). 9789401176057, Academia Publishing House of Czechoslovak Academy of Sciences. ISBN 9789401176057
Precursors
Semisynthesis
The semisynthesis of steroids often begins from precursors such as cholesterol, , or . The efforts of Syntex, a company involved in the Mexican barbasco trade, used Dioscorea mexicana to produce the sapogenin diosgenin in the early days of the synthetic steroid pharmaceutical industry.
Total synthesis
Some steroidal hormones are economically obtained only by total synthesis from (e.g. 13-alkyl steroids). For example, the pharmaceutical Norgestrel begins from methoxy-1-tetralone, a petrochemical derived from phenol.
Research awards
A number of have been awarded for steroid research, including:
See also
Bibliography
(2025). 9780854044641, RSC Publ.. ISBN 9780854044641
(2025). 9780470660850, Wiley. ISBN 9780470660850 A concise history of the study of steroids.
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