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Accession NumberDB02187  (EXPT01355)
TypeSmall Molecule

An estrogenic steroid produced by horses. It has a total of four double bonds in the A- and B-ring. High concentration of euilin is found in the urine of pregnant mares. [PubChem]

Equilin is one of the estrogens present in the mixture of estrogens isolated from horse urine and marketed as Premarin. Premarin became the most commonly used form of estrogen for hormone replacement therapy in the United States of America. Estrone is the major estrogen in Premarin (about 50%) and equilin is present as about 25% of the total. Estrone is a major estrogen that is normally found in women. Equilin is not normally present in women, so there has been interest in the effects of equilin on the human body. [Wikipedia]

The estrogens in Premarin are present mainly as “conjugates”, modified chemical forms in which the active estrogen is coupled to another chemical group such as sulfate. Estrone sulfate is usually the major form of estrogen in women. After being taken into a woman’s body, the conjugated estrogens of Premarin are converted to the active unconjugated estrogens or excreted from the woman’s body. Estrone can be converted to estradiol, which is thought to be the major active estrogen in women. [Wikipedia]

1,3,5,7-Estratetraen-3-ol-17-oneNot AvailableNot Available
7-DehydroestroneNot AvailableNot Available
DihydroequileninNot AvailableNot Available
EquilinNot AvailableNot Available
Prescription ProductsNot Available
Generic Prescription ProductsNot Available
Over the Counter ProductsNot Available
International BrandsNot Available
Brand mixturesNot Available
SaltsNot Available
CategoriesNot Available
CAS number474-86-2
WeightAverage: 268.3502
Monoisotopic: 268.146329884
Chemical FormulaC18H20O2
DescriptionThis compound belongs to the class of organic compounds known as oxosteroids. These are steroid derivatives carrying a C=O group attached to steroid skeleton.
KingdomOrganic compounds
Super ClassLipids and lipid-like molecules
ClassSteroids and steroid derivatives
Sub ClassOxosteroids
Direct ParentOxosteroids
Alternative Parents
  • Oxosteroid
  • 17-oxosteroid
  • Hydroxysteroid
  • 3-hydroxysteroid
  • 3-hydroxy-delta-7-steroid
  • Delta-7-steroid
  • Phenanthrene
  • Naphthalene
  • Benzenoid
  • Ketone
  • Hydrocarbon derivative
  • Organooxygen compound
  • Carbonyl group
  • Aromatic homopolycyclic compound
Molecular FrameworkAromatic homopolycyclic compounds
External Descriptors
IndicationFor the treatment of moderate to severe vasomotor symptoms associated with the menopause, atrophic vaginitis, osteoporosis, hypoestrogenism due to hypogonadism, castration, primary ovarian failure, breast cancer (for palliation only), and Advanced androgen-dependent carcinoma of the prostate (for palliation only)
PharmacodynamicsEquilin is a component of Premarin (conjugated estrogens), a mixture of the water soluble salts of sulfate esters from estrone, equilin, 17 alpha-dihydroequilin, and other related steroids, may be derived from pregnant equine urine or yam and soy plants. Estrogens are important in the development and maintenance of the female reproductive system and secondary sex characteristics. They promote growth and development of the vagina, uterus, and fallopian tubes, and enlargement of the breasts. Indirectly, they contribute to the shaping of the skeleton, maintenance of tone and elasticity of urogenital structures, changes in the epiphyses of the long bones that allow for the pubertal growth spurt and its termination, growth of axillary and pubic hair, and pigmentation of the nipples and genitals. Decline of estrogenic activity at the end of the menstrual cycle can bring on menstruation, although the cessation of progesterone secretion is the most important factor in the mature ovulatory cycle. However, in the preovulatory or nonovulatory cycle, estrogen is the primary determinant in the onset of menstruation. Estrogens also affect the release of pituitary gonadotropins. The pharmacologic effects of conjugated estrogens are similar to those of endogenous estrogens.
Mechanism of actionEstrogens enter the cells of responsive tissues (e.g., female organs, breasts, hypothalamus, pituitary) where they interact with a protein receptor, subsequently increasing the rate of synthesis of DNA, RNA, and some proteins. Estrogens decrease the secretion of gonadotropin-releasing hormone by the hypothalamus, reducing the secretion of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the pituitary.
AbsorptionWell absorbed.
Volume of distributionNot Available
Protein binding90% bound to plasma proteins


Route of eliminationNot Available
Half lifeNot Available
ClearanceNot Available
ToxicityNot Available
Affected organisms
  • Humans and other mammals
PathwaysNot Available
SNP Mediated EffectsNot Available
SNP Mediated Adverse Drug ReactionsNot Available
Predicted ADMET features
Human Intestinal Absorption+1.0
Blood Brain Barrier+0.9192
Caco-2 permeable+0.875
P-glycoprotein substrateSubstrate0.6807
P-glycoprotein inhibitor INon-inhibitor0.8085
P-glycoprotein inhibitor IINon-inhibitor0.8881
Renal organic cation transporterNon-inhibitor0.6704
CYP450 2C9 substrateNon-substrate0.7245
CYP450 2D6 substrateNon-substrate0.9081
CYP450 3A4 substrateSubstrate0.7666
CYP450 1A2 substrateInhibitor0.9108
CYP450 2C9 substrateNon-inhibitor0.9071
CYP450 2D6 substrateNon-inhibitor0.9231
CYP450 2C19 substrateInhibitor0.8209
CYP450 3A4 substrateNon-inhibitor0.8156
CYP450 inhibitory promiscuityLow CYP Inhibitory Promiscuity0.5528
Ames testNon AMES toxic0.9109
BiodegradationNot ready biodegradable0.9319
Rat acute toxicity1.8021 LD50, mol/kg Not applicable
hERG inhibition (predictor I)Weak inhibitor0.7619
hERG inhibition (predictor II)Non-inhibitor0.601
ManufacturersNot Available
PackagersNot Available
Dosage formsNot Available
PricesNot Available
PatentsNot Available
Experimental Properties
melting point239 °CPhysProp
water solubility1.41 mg/L (at 25 °C)YALKOWSKY,SH & DANNENFELSER,RM (1992)
Predicted Properties
Water Solubility0.0133 mg/mLALOGPS
pKa (Strongest Acidic)9.41ChemAxon
pKa (Strongest Basic)-6ChemAxon
Physiological Charge0ChemAxon
Hydrogen Acceptor Count2ChemAxon
Hydrogen Donor Count1ChemAxon
Polar Surface Area37.3 Å2ChemAxon
Rotatable Bond Count0ChemAxon
Refractivity79.93 m3·mol-1ChemAxon
Polarizability30.55 Å3ChemAxon
Number of Rings4ChemAxon
Rule of FiveYesChemAxon
Ghose FilterYesChemAxon
Veber's RuleYesChemAxon
MDDR-like RuleYesChemAxon
Mass Spec (NIST)Not Available
SpectraMS1D NMR
Synthesis ReferenceNot Available
General Reference
  1. Sawicki MW, Erman M, Puranen T, Vihko P, Ghosh D: Structure of the ternary complex of human 17beta-hydroxysteroid dehydrogenase type 1 with 3-hydroxyestra-1,3,5,7-tetraen-17-one (equilin) and NADP+. Proc Natl Acad Sci U S A. 1999 Feb 2;96(3):840-5. Pubmed
External Links
ATC CodesNot Available
AHFS CodesNot Available
PDB Entries
FDA labelNot Available
MSDSNot Available
Drug InteractionsNot Available
Food InteractionsNot Available


1. Estradiol 17-beta-dehydrogenase 1

Kind: protein

Organism: Human

Pharmacological action: unknown


Name UniProt ID Details
Estradiol 17-beta-dehydrogenase 1 P14061 Details


  1. Overington JP, Al-Lazikani B, Hopkins AL: How many drug targets are there? Nat Rev Drug Discov. 2006 Dec;5(12):993-6. Pubmed
  2. Imming P, Sinning C, Meyer A: Drugs, their targets and the nature and number of drug targets. Nat Rev Drug Discov. 2006 Oct;5(10):821-34. Pubmed
  3. Berman HM, Westbrook J, Feng Z, Gilliland G, Bhat TN, Weissig H, Shindyalov IN, Bourne PE: The Protein Data Bank. Nucleic Acids Res. 2000 Jan 1;28(1):235-42. Pubmed

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Drug created on June 13, 2005 07:24 / Updated on September 16, 2013 17:17