Steroids are compounds consistuted of four fused rings, for example, the most common and best known steroid in humans, cholesterol. In animals, steroids are biosynthesized from lanosterol and are widely distributed. The distinctive feature in steroids is lack of methyl group at C-4 position as compared to terpenes. In this section, we have classified steroids into five basic categories based upon their chemical composition (Fig.1). Vitamin D, another steroid derivative, is described on "Vitamins".

●Steroid Hormones: Estranes, Androstanes, Pregnanes
Certain kinds of steroids like estrogenes, androstanes and pregnanes can act as hormones, their activities being closely related to their structures (Table 1). Pregnane-type steroids can be classified into glucocorticoids and progestogens based on their bioactivities. Their classification and the typical compounds in each category are illustrated as follows:

Estrogens: Estrogens function as the primary female sex hormone and in combination with synthetic progestogens can be used as oral contraceptives to suppress ovulation. Recently, it is also reported that they are effective for the prevention of osteoporosis, heart attacks and Alzheimer’s disease in women.
Androgens: Testosterone is not only the principal and most well known male sex hormone but is also known to exert anabolic effects. This is also the main reason why some of them have been banned from use as bone density enhancers and muscle-building drugs by several sports organizations. They are also the intermediates of estrogene biosynthetic pathway or rather the precursors of all estrogens.
Progestogens: The only naturally occuring progestogen, i.e., progesterone, exhibits antiovulatory action. Based on its structure, derivatives of 19-nortestosterone were synthesized and can be used as oral contraceptives.
Glucocorticoids: Synthetic glucocorticoids such as dexamethasone and prednisolone find clinical use as anti-inflammatory agents. They are synthetically developed based on the structure of cortisone, a natural glucocorticoid.

WARNING
Some of the steroid hormones may cause serious physiological actions. To avoid inhalation and contacting with skin, wear protective goggles, mask and eyeglasses when handling. Sufficient caution should be taken, when using these compounds, from the opening up to the disposal of the reagents.

●Bile Acids: Cholanes
Cholane type steroids are predominantly found in the bile. Cholic acid and its derivatives exist in bile as the major component as conjugates of glycine and taurine. Since conjugated cholates are amphiphilic, they assist in the digestion and absorption of lipids in small intestine. This characteristic is also exploited also in its use as a surfactant.

●Cholesterol: Cholestanes
Cholesterol possesses a cholestane-type skeleton and in conjugation with fatty acids, it forms the main component of cell membranes in animals and microorganisms. These cholesterol conjugates establish and maintain proper membrane permeability. In addition, it is a precursor of steroids as mentioned above and also exists in its liberated form in organisms.

●Phytosteroids, Steroid Glycosides, Miscellaneous Steroids
Steroids of plant origin have different biosynthetic pathways: they are synthesized from cycloartenol. They possess structural features distinct from animal steroids, for instance, a characteristic alkyl side-chain at C-24. Steroid glycosides and their aglycones are also listed in this section.

Estranes

Androstanes

Pregnanes

Cholanes (Bile Acids)

Cholestanes

Phytosteroids, Steroid Glycosides & Other Steroids

Estranes

E0025	E0329	E0875
E0876	E0218	E0026
E0037	M0728

E0025	beta-Estradiol
E0329	Estradiol Benzoate
E0875	beta-Estradiol 17-Cypionate
E0876	beta-Estradiol 17-Valerate
E0218	Estriol
E0026	Estrone
E0037	Ethynylestradiol
M0728	Mestranol

Androstanes

A1397	A0856	A0845
A0646	D0044	D0045
E0374	H1193	M1800
M1801	M0146	M0435
M0638	O0322	S0520
A0462	S0530	T0027
T0028

A1397	Adrenosterone
A0856	1,4-Androstadiene-3,17-dione
A0845	DELTA4-Androstene-3,17-dione
A0646	Androsterone
D0044	Dehydroepiandrosterone
D0045	Dehydroepiandrosterone Acetate
E0374	Epiandrosterone from Wool Fat
H1193	17beta-Hydroxy-17-methylandrosta-1,4-dien-3-one
M1800	1alpha-Methylandrostan-17beta-ol-3-one
M1801	17alpha-Methylandrostan-17beta-ol-3-one
M0146	Methylandrostenediol
M0435	Methyltestosterone
M0638	DELTA9(11)-Methyltestosterone
O0322	Oxymetholone
S0520	Sodium Dehydroepiandrosterone-3-sulfate Hydrate
A0462	Stanolone
S0530	Stanozolol
T0027	Testosterone
T0028	Testosterone Propionate

Pregnanes

Progestogen

E0015	E0198	F0414
H0498	H1250	H0499
H0994	M1964	M1949
P0678	P0771	P0786
P0477	P0478

E0015	16,17-Epoxypregnenolone Acetate
E0198	16,17-Epoxyprogesterone
F0414	Fluorometholone
H0498	11alpha-Hydroxyprogesterone
H1250	17alpha-Hydroxyprogesterone
H0499	11alpha-Hydroxyprogesterone Acetate
H0994	17alpha-Hydroxyprogesterone Caproate
M1964	Medroxyprogesterone Acetate
M1949	Megestrol Acetate
P0678	5beta-Pregnane-3alpha,20alpha-diol
P0771	4-Pregnene-3,11,20-trione
P0786	Pregnenolone
P0477	Pregnenolone Acetate
P0478	Progesterone

Glucocorticoids

B1837	B3165	B3166
C1478	C0388	C1479
C1317	C0389	D0047
D1961	D3628	D3918
F0437	F0657	F0525
H0533	H0184	P0637
P1283	P1276	T2303
T2308

B1837	Betamethasone
B3165	Betamethasone 21-Acetate
B3166	Betamethasone 17,21-Dipropionate
C1478	Cortexolone
C0388	Corticosterone
C1479	Corticosterone 21-Acetate
C1317	Cortisone
C0389	Cortisone Acetate
D0047	Deoxycorticosterone Acetate
D1961	Dexamethasone
D3628	Dexamethasone 21-Acetate
D3918	Disodium Prednisolone 21-Phosphate
F0437	Flunisolide
F0657	Fluocinolone Acetonide
F0525	Fluticasone Propionate
H0533	Hydrocortisone
H0184	Hydrocortisone Acetate
P0637	Prednisolone
P1283	Prednisolone Acetate
P1276	Prednisone
T2303	Triamcinolone
T2308	Triamcinolone Acetonide

Cholanes (Bile Acids)

C0750	C1578	C0324
D0042	C0315	H0521
H0869	H0535	L0089
C1412	H0529	O0267
C0325	S0596	D0043
C0316	D1820	G0207
H0870	T0808	U0068
T1567	U0030

C0750	Chenodeoxycholic Acid
C1578	3-[(3-Cholamidopropyl)dimethylammonio]-1-propanesulfonate
C0324	Cholic Acid
D0042	Dehydrocholic Acid
C0315	Deoxycholic Acid
H0521	3beta-Hydroxy-DELTA5-cholenic Acid
H0869	3alpha-Hydroxy-7-oxo-5beta-cholanic Acid
H0535	Hyodeoxycholic Acid
L0089	Lithocholic Acid
C1412	Methyl Cholate
H0529	Methyl Hyodeoxycholate
O0267	12-Oxochenodeoxycholic Acid
C0325	Sodium Cholate
S0596	Sodium Cholate from Bovine Bile [for Biochemical Research]
D0043	Sodium Dehydrocholate
C0316	Sodium Deoxycholate
D1820	Sodium Deoxycholate [for Electrophoresis]
G0207	Sodium Glycocholate Hydrate
H0870	Sodium Hyodeoxycholate
T0808	Sodium Taurocholate from Bovine Bile
U0068	Sodium Ursodeoxycholate Hydrate
T1567	Tauroursodeoxycholic Acid Dihydrate
U0030	Ursodeoxycholic Acid

Cholestanes

C0317	C1366	C0318
C1222	C0695	C0610

C0317	beta-Cholestanol (contains alpha-Cholestanol)
C1366	(+)-4-Cholesten-3-one
C0318	Cholesterol
C1222	Cholesterol-5alpha,6alpha-epoxide
C0695	Cholesteryl Bromide from Beef Fat
C0610	Cholesteryl Chloride from Beef Fat

Phytosteroids, Steroid Glycosides & Other Steroids

Phytosteroids

E0018	S0040	S0221
S0386	S0088

E0018	Ergosterol
S0040	beta-Sitosterol (contains Campesterol)
S0221	beta-Sitosterol Acetate (contains Campesterol Acetate)
S0386	Stigmastanol
S0088	Stigmasterol

Steroid Glycosides

D0540	D0542	D1828
S0091	T0329

D0540	Digitonin
D0542	Digitoxin
D1828	Digoxin
S0091	g-Strophanthin Octahydrate
T0329	Tomatine [for Cholesterol assay]

Other Steroids

D0541	D1474	E0040
F0675	H0003	M1732
N0777	N0449	N0450
N0889	S0260	T2330
T2328

D0541	Digitoxigenin
D1474	Diosgenin
E0040	Ethisterone
F0675	Finasteride
H0003	Hecogenin
M1732	Mifepristone
N0777	Nandrolone
N0449	Norethisterone
N0450	Norethisterone Acetate
N0889	(-)-Norgestrel
S0260	Spironolactone
T2330	Tibolone
T2328	Trenbolone

Vitamins