17β-Dihydroequilin

17β-Dihydroequilin
Clinical data
Other names	β-Dihydroequilin; Δ7-17β-Estradiol; 7-Dehydro-17β-estradiol; Estra-1,3,5(10),7-tetraen-3,17β-diol; NSC-12170
Routes of; administration	By mouth
Drug class	Estrogen
Identifiers
	IUPAC name (9S,13S,14S,17S)-13-Methyl-6,9,11,12,14,15,16,17-octahydrocyclopenta[a]phenanthrene-3,17-diol;
CAS Number	3563-27-7;
PubChem CID	11954027;
ChemSpider	10128322;
UNII	WXG88DST4R;
ChEBI	CHEBI:62851;
ChEMBL	ChEMBL121458;
CompTox Dashboard (EPA)	DTXSID40871892 ;
ECHA InfoCard	100.020.576
Chemical and physical data
Formula	C18H22O22
Molar mass	590.352 g·mol−1
3D model (JSmol)	Interactive image;
	SMILES C[C@]12CC[C@H]3C(=CCC4=C3C=CC(=C4)O)[C@@H]1CC[C@@H]2O;
	InChI InChI=1S/C18H22O2/c1-18-9-8-14-13-5-3-12(19)10-11(13)2-4-15(14)16(18)6-7-17(18)20/h3-5,10,14,16-17,19-20H,2,6-9H2,1H3/t14-,16+,17+,18+/m1/s1; Key:NLLMJANWPUQQTA-UBDQQSCGSA-N;

17β-Dihydroequilin is a naturally occurring estrogen sex hormone found in horses as well as a medication.[1][2] As the C3 sulfate ester sodium salt, it is a minor constituent (1.7%) of conjugated estrogens (CEEs; brand name Premarin).[1] However, as equilin, with equilin sulfate being a major component of CEEs, is transformed into 17β-dihydroequilin in the body, analogously to the conversion of estrone into estradiol, 17β-dihydroequilin is, along with estradiol, the most important estrogen responsible for the effects of CEEs.[1]

Pharmacology

Pharmacodynamics

17β-Dihydroequilin is an estrogen, or an agonist of the estrogen receptors (ERs), the ERα and ERβ.[1] In terms of relative binding affinity for the ERs, 17β-dihydroequilin has about 113% and 108% of that of estradiol for the ERα and ERβ, respectively.[1] 17β-Dihydroequilin has about 83% of the relative potency of CEEs in the vagina and 200% of the relative potency of CEEs in the uterus.[1] Of the equine estrogens, it shows the highest estrogenic activity and greatest estrogenic potency.[1]

Like CEEs as a whole, 17β-dihydroequilin has disproportionate effects in certain tissues such as the liver and uterus.[1] Equilin, the second major component of conjugated estrogens after estrone, is reversibly transformed into 17β-dihydroequilin analogously to the transformation of estrone into estradiol.[1] However, whereas the balance of mutual interconversion of estrone and estradiol is largely shifted in the direction of estrone, it is nearly equal in the case of equilin and 17β-dihydroequilin.[1] As such, although 17β-dihydroequilin is only a minor constituent of CEEs, it is, along with estradiol, the most important estrogen relevant to the estrogenic activity of the medication.[1]

Composition of conjugated estrogens and properties of constituents
Compound	Synonym	Proportion (%)	Relative potency in the vagina (%)	Relative potency in the uterus (%)	RBA for ERα (%)	RBA for ERβ (%)	ERα / ERβ RBA ratio
Conjugated estrogens	–	100	38	100	–	–	–
Estrone	–	49.1–61.5	30	32	26	52	0.50
Equilin	Δ⁷-Estrone	22.4–30.5	42	80	13	49	0.26
17α-Dihydroequilin	Δ⁷-17α-Estradiol	13.5–19.5	0.06	2.6	41	32	1.30
17α-Estradiol	–	2.5–9.5	0.11	3.5	19	42	0.45
Δ⁸-Estrone	–	3.5–3.9	?	?	19	32	0.60
Equilenin	Δ^6,8-Estrone	2.2–2.8	1.3	11.4	15	20–29	0.50–0.75
17β-Dihydroequilin	Δ⁷-17β-Estradiol	0.5–4.0	83	200	113	108	1.05
17α-Dihydroequilenin	Δ^6,8-17α-Estradiol	1.2–1.6	0.018	1.3	20	49	0.40
17β-Estradiol	–	0.56–0.9	100	?	100	100	1.00
17β-Dihydroequilenin	Δ^6,8-17β-Estradiol	0.5–0.7	0.21	9.4	68	90	0.75
Δ⁸-17β-Estradiol	–	Small amounts	?	?	68	72	0.94
Notes: All listed compounds are present in conjugated estrogen products specifically in the form of the sodium salts of the sulfate esters (i.e., as sodium estrone sulfate, sodium equilin sulfate, etc.). Sources: See template.

Relative oral potencies of estrogens
Estrogen	Type	HF	VE	UCa	FSH	LH	HDL-C	SHBG	CBG	AGT	Liver
Estradiol	Bioidentical	1.0	1.0	1.0	1.0	1.0	1.0	1.0	1.0	1.0	1.0
Estrone	Bioidentical	?	?	?	0.3	0.3	?	?	?	?	?
Estriol	Bioidentical	0.3	0.3	0.1	0.3	0.3	0.2	?	?	?	0.67
Estrone sulfate	Bioidentical	?	0.9	0.9	0.8–0.9	0.9	0.5	0.9	0.5–0.7	1.4–1.5	0.56–1.7
Conjugated estrogens	Natural	1.2	1.5	2.0	1.1–1.3	1.0	1.5	3.0–3.2	1.3–1.5	5.0	1.3–4.5
Equilin sulfate	Natural	?	?	1.0	?	?	6.0	7.5	6.0	7.5	?
Ethinylestradiol	Synthetic	120	150	400	60–150	100	400	500–600	500–600	350	2.9–5.0
Diethylstilbestrol	Synthetic	?	?	?	2.9–3.4	?	?	26–28	25–37	20	5.7–7.5
Notes: Values are ratios, with estradiol as standard (i.e., 1.0). Abbreviations: HF = Clinical relief of hot flashes. VE = Increased proliferation of vaginal epithelium. UCa = Decrease in UCa. FSH = Suppression of FSH levels. LH = Suppression of LH levels. HDL-C, SHBG, CBG, and AGT = Increase in the serum levels of these liver proteins. Liver = Ratio of liver estrogenic effects to general/systemic estrogenic effects (specifically hot flashes relief and gonadotropin suppression). Type: Bioidentical = Identical to those found in humans. Natural = Naturally occurring but not identical to those found in humans (e.g., estrogens of other species). Synthetic = Man-made, does not occur naturally in animals or in the environment. Sources: See template.

Pharmacokinetics

17β-Dihydroequilin has about 30% of the relative binding affinity of testosterone for sex hormone-binding globulin (SHBG), relative to 50% for estradiol.[1] The metabolic clearance rate of 17β-dihydroequilin is 1,250 L/day/m², relative to 580 L/day/m² for estradiol.[1]

Chemistry

17β-Dihydroequilin, or simply β-dihydroequilin, also known as δ⁷-17β-estradiol or as 7-dehydro-17β-estradiol, as well as estra-1,3,5(10),7-tetraen-3,17β-diol, is a naturally occurring estrane steroid and an analogue of estradiol.[1] In terms of chemical structure and pharmacology, equilin (δ⁷-estrone) is to 17β-dihydroequilin as estrone is to estradiol.[1]

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References

Kuhl H (2005). "Pharmacology of estrogens and progestogens: influence of different routes of administration" (PDF). Climacteric. 8 Suppl 1: 3–63. doi:10.1080/13697130500148875. PMID 16112947.
Marc A. Fritz; Leon Speroff (28 March 2012). Clinical Gynecologic Endocrinology and Infertility. Lippincott Williams & Wilkins. pp. 751–. ISBN 978-1-4511-4847-3.

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[pmid16112947-1] Kuhl H (2005). "Pharmacology of estrogens and progestogens: influence of different routes of administration" (PDF). Climacteric. 8 Suppl 1: 3–63. doi:10.1080/13697130500148875. PMID 16112947.

[FritzSperoff2012-2] Marc A. Fritz; Leon Speroff (28 March 2012). Clinical Gynecologic Endocrinology and Infertility. Lippincott Williams & Wilkins. pp. 751–. ISBN 978-1-4511-4847-3.