# Stilbestrol

Stilbestrol, or stilboestrol, also known as 4,4'-dihydroxystilbene or 4,4'-stilbenediol, is a stilbenoid nonsteroidal estrogen and the parent compound of a group of more potent nonsteroidal estrogen derivatives that includes, most notably, diethylstilbestrol (DES). The term "stilbestrol" is often used incorrectly to refer to DES, but they are not the same compound.
Stilbestrol itself is an active estrogen but is less potent than DES and other derivatives.

## Stilbestrol derivatives

The stilbestrol estrogenic drugs include the following:
* Acefluranol (an antiestrogen)
* Benzestrol (technically not a stilbestrol derivative due to its elongated central chain, but a very close analogue and grouped with the stilbestrol estrogens in any case)
* Bifluranol
* Dienestrol
** Dienestrol acetate
* Diethylstilbestrol (commonly, but erroneously shortened to simply “stilbestrol”)
** Diethylstilbestrol diacetate
** Diethylstilbestrol dilaurate
** Diethylstilbestrol dipalmitate
** Diethylstilbestrol dipropionate
** Diethylstilbestrol disulfate
** Diethylstilbestrol monobenzyl ether
** Dimestrol (dianisylhexene, diethylstilbestrol dimethyl ether, dimethoxydiethylstilbene)
** Fosfestrol (diethylstilbestrol diphosphate)
** Furostilbestrol (diethylstilbestrol difuroate)
** ICI-85966 (diethylstilbestrol bis[di(2-chloroethyl)carbamate)
** Mestilbol (diethylstilbestrol monomethyl ether)
* Dimethylstilbestrol
* Hexestrol (dihydrodiethylstilbestrol)
** Diaethiphenum (hexestrol bis(2-diethylaminoethyl) ether) (a coronary vasodilator)
** Hexestrol diacetate
** Hexestrol dicaprylate
** Hexestrol diphosphate
** Hexestrol dipropionate
** Phenestrol (hexestrol bis[4-[bis(2-chloroethyl)amino]phenylacetate)
* Methestrol (promethestrol; dimethylhexestrol)
** Methestrol dipropionate (promethestrol dipropionate)
* Pentafluranol
* Terfluranol
Of the stilbestrol estrogens, diethylstilbestrol, hexestrol, and benzestrol are the most well-known.

### Mechanism of action

The stilbestrol estrogens bind with high affinity to both ERα and ERβ.
vte Affinities of estrogen receptor ligands for the ERα and ERβ :
| Ligand | Other names | Relative binding affinities (RBA, %)$^a$ | Relative binding affinities (RBA, %)$^a$ | Absolute binding affinities (K$_i$, nM)$^a$ | Absolute binding affinities (K$_i$, nM)$^a$ | Action |
| Ligand | Other names | ERα | ERβ | ERα | ERβ | Action |
| Estradiol | E2; 17β-Estradiol | 100 | 100 | 0.115 (0.04–0.24) | 0.15 (0.10–2.08) | Estrogen |
| Estrone | E1; 17-Ketoestradiol | 16.39 (0.7–60) | 6.5 (1.36–52) | 0.445 (0.3–1.01) | 1.75 (0.35–9.24) | Estrogen |
| Estriol | E3; 16α-OH-17β-E2 | 12.65 (4.03–56) | 26 (14.0–44.6) | 0.45 (0.35–1.4) | 0.7 (0.63–0.7) | Estrogen |
| Estetrol | E4; 15α,16α-Di-OH-17β-E2 | 4.0 | 3.0 | 4.9 | 19 | Estrogen |
| Alfatradiol | 17α-Estradiol | 20.5 (7–80.1) | 8.195 (2–42) | 0.2–0.52 | 0.43–1.2 | Metabolite |
| 16-Epiestriol | 16β-Hydroxy-17β-estradiol | 7.795 (4.94–63) | 50 | ? | ? | Metabolite |
| 17-Epiestriol | 16α-Hydroxy-17α-estradiol | 55.45 (29–103) | 79–80 | ? | ? | Metabolite |
| 16,17-Epiestriol | 16β-Hydroxy-17α-estradiol | 1.0 | 13 | ? | ? | Metabolite |
| 2-Hydroxyestradiol | 2-OH-E2 | 22 (7–81) | 11–35 | 2.5 | 1.3 | Metabolite |
| 2-Methoxyestradiol | 2-MeO-E2 | 0.0027–2.0 | 1.0 | ? | ? | Metabolite |
| 4-Hydroxyestradiol | 4-OH-E2 | 13 (8–70) | 7–56 | 1.0 | 1.9 | Metabolite |
| 4-Methoxyestradiol | 4-MeO-E2 | 2.0 | 1.0 | ? | ? | Metabolite |
| 2-Hydroxyestrone | 2-OH-E1 | 2.0–4.0 | 0.2–0.4 | ? | ? | Metabolite |
| 2-Methoxyestrone | 2-MeO-E1 | <0.001–<1 | <1 | ? | ? | Metabolite |
| 4-Hydroxyestrone | 4-OH-E1 | 1.0–2.0 | 1.0 | ? | ? | Metabolite |
| 4-Methoxyestrone | 4-MeO-E1 | <1 | <1 | ? | ? | Metabolite |
| 16α-Hydroxyestrone | 16α-OH-E1; 17-Ketoestriol | 2.0–6.5 | 35 | ? | ? | Metabolite |
| 2-Hydroxyestriol | 2-OH-E3 | 2.0 | 1.0 | ? | ? | Metabolite |
| 4-Methoxyestriol | 4-MeO-E3 | 1.0 | 1.0 | ? | ? | Metabolite |
| Estradiol sulfate | E2S; Estradiol 3-sulfate | <1 | <1 | ? | ? | Metabolite |
| Estradiol disulfate | Estradiol 3,17β-disulfate | 0.0004 | ? | ? | ? | Metabolite |
| Estradiol 3-glucuronide | E2-3G | 0.0079 | ? | ? | ? | Metabolite |
| Estradiol 17β-glucuronide | E2-17G | 0.0015 | ? | ? | ? | Metabolite |
| Estradiol 3-gluc. 17β-sulfate | E2-3G-17S | 0.0001 | ? | ? | ? | Metabolite |
| Estrone sulfate | E1S; Estrone 3-sulfate | <1 | <1 | >10 | >10 | Metabolite |
| Estradiol benzoate | EB; Estradiol 3-benzoate | 10 | ? | ? | ? | Estrogen |
| Estradiol 17β-benzoate | E2-17B | 11.3 | 32.6 | ? | ? | Estrogen |
| Estrone methyl ether | Estrone 3-methyl ether | 0.145 | ? | ? | ? | Estrogen |
| ent-Estradiol | 1-Estradiol | 1.31–12.34 | 9.44–80.07 | ? | ? | Estrogen |
| Equilin | 7-Dehydroestrone | 13 (4.0–28.9) | 13.0–49 | 0.79 | 0.36 | Estrogen |
| Equilenin | 6,8-Didehydroestrone | 2.0–15 | 7.0–20 | 0.64 | 0.62 | Estrogen |
| 17β-Dihydroequilin | 7-Dehydro-17β-estradiol | 7.9–113 | 7.9–108 | 0.09 | 0.17 | Estrogen |
| 17α-Dihydroequilin | 7-Dehydro-17α-estradiol | 18.6 (18–41) | 14–32 | 0.24 | 0.57 | Estrogen |
| 17β-Dihydroequilenin | 6,8-Didehydro-17β-estradiol | 35–68 | 90–100 | 0.15 | 0.20 | Estrogen |
| 17α-Dihydroequilenin | 6,8-Didehydro-17α-estradiol | 20 | 49 | 0.50 | 0.37 | Estrogen |
| Δ$^8$-Estradiol | 8,9-Dehydro-17β-estradiol | 68 | 72 | 0.15 | 0.25 | Estrogen |
| Δ$^8$-Estrone | 8,9-Dehydroestrone | 19 | 32 | 0.52 | 0.57 | Estrogen |
| Ethinylestradiol | EE; 17α-Ethynyl-17β-E2 | 120.9 (68.8–480) | 44.4 (2.0–144) | 0.02–0.05 | 0.29–0.81 | Estrogen |
| Mestranol | EE 3-methyl ether | ? | 2.5 | ? | ? | Estrogen |
| Moxestrol | RU-2858; 11β-Methoxy-EE | 35–43 | 5–20 | 0.5 | 2.6 | Estrogen |
| Methylestradiol | 17α-Methyl-17β-estradiol | 70 | 44 | ? | ? | Estrogen |
| Diethylstilbestrol | DES; Stilbestrol | 129.5 (89.1–468) | 219.63 (61.2–295) | 0.04 | 0.05 | Estrogen |
| Hexestrol | Dihydrodiethylstilbestrol | 153.6 (31–302) | 60–234 | 0.06 | 0.06 | Estrogen |
| Dienestrol | Dehydrostilbestrol | 37 (20.4–223) | 56–404 | 0.05 | 0.03 | Estrogen |
| Benzestrol (B2) | – | 114 | ? | ? | ? | Estrogen |
| Chlorotrianisene | TACE | 1.74 | ? | 15.30 | ? | Estrogen |
| Triphenylethylene | TPE | 0.074 | ? | ? | ? | Estrogen |
| Triphenylbromoethylene | TPBE | 2.69 | ? | ? | ? | Estrogen |
| Tamoxifen | ICI-46,474 | 3 (0.1–47) | 3.33 (0.28–6) | 3.4–9.69 | 2.5 | SERM |
| Afimoxifene | 4-Hydroxytamoxifen; 4-OHT | 100.1 (1.7–257) | 10 (0.98–339) | 2.3 (0.1–3.61) | 0.04–4.8 | SERM |
| Toremifene | 4-Chlorotamoxifen; 4-CT | ? | ? | 7.14–20.3 | 15.4 | SERM |
| Clomifene | MRL-41 | 25 (19.2–37.2) | 12 | 0.9 | 1.2 | SERM |
| Cyclofenil | F-6066; Sexovid | 151–152 | 243 | ? | ? | SERM |
| Nafoxidine | U-11,000A | 30.9–44 | 16 | 0.3 | 0.8 | SERM |
| Raloxifene | – | 41.2 (7.8–69) | 5.34 (0.54–16) | 0.188–0.52 | 20.2 | SERM |
| Arzoxifene | LY-353,381 | ? | ? | 0.179 | ? | SERM |
| Lasofoxifene | CP-336,156 | 10.2–166 | 19.0 | 0.229 | ? | SERM |
| Ormeloxifene | Centchroman | ? | ? | 0.313 | ? | SERM |
| Levormeloxifene | 6720-CDRI; NNC-460,020 | 1.55 | 1.88 | ? | ? | SERM |
| Ospemifene | Deaminohydroxytoremifene | 0.82–2.63 | 0.59–1.22 | ? | ? | SERM |
| Bazedoxifene | – | ? | ? | 0.053 | ? | SERM |
| Etacstil | GW-5638 | 4.30 | 11.5 | ? | ? | SERM |
| ICI-164,384 | – | 63.5 (3.70–97.7) | 166 | 0.2 | 0.08 | Antiestrogen |
| Fulvestrant | ICI-182,780 | 43.5 (9.4–325) | 21.65 (2.05–40.5) | 0.42 | 1.3 | Antiestrogen |
| Propylpyrazoletriol | PPT | 49 (10.0–89.1) | 0.12 | 0.40 | 92.8 | ERα agonist |
| 16α-LE2 | 16α-Lactone-17β-estradiol | 14.6–57 | 0.089 | 0.27 | 131 | ERα agonist |
| 16α-Iodo-E2 | 16α-Iodo-17β-estradiol | 30.2 | 2.30 | ? | ? | ERα agonist |
| Methylpiperidinopyrazole | MPP | 11 | 0.05 | ? | ? | ERα antagonist |
| Diarylpropionitrile | DPN | 0.12–0.25 | 6.6–18 | 32.4 | 1.7 | ERβ agonist |
| 8β-VE2 | 8β-Vinyl-17β-estradiol | 0.35 | 22.0–83 | 12.9 | 0.50 | ERβ agonist |
| Prinaberel | ERB-041; WAY-202,041 | 0.27 | 67–72 | ? | ? | ERβ agonist |
| ERB-196 | WAY-202,196 | ? | 180 | ? | ? | ERβ agonist |
| Erteberel | SERBA-1; LY-500,307 | ? | ? | 2.68 | 0.19 | ERβ agonist |
| SERBA-2 | – | ? | ? | 14.5 | 1.54 | ERβ agonist |
| Coumestrol | – | 9.225 (0.0117–94) | 64.125 (0.41–185) | 0.14–80.0 | 0.07–27.0 | Xenoestrogen |
| Genistein | – | 0.445 (0.0012–16) | 33.42 (0.86–87) | 2.6–126 | 0.3–12.8 | Xenoestrogen |
| Equol | – | 0.2–0.287 | 0.85 (0.10–2.85) | ? | ? | Xenoestrogen |
| Daidzein | – | 0.07 (0.0018–9.3) | 0.7865 (0.04–17.1) | 2.0 | 85.3 | Xenoestrogen |
| Biochanin A | – | 0.04 (0.022–0.15) | 0.6225 (0.010–1.2) | 174 | 8.9 | Xenoestrogen |
| Kaempferol | – | 0.07 (0.029–0.10) | 2.2 (0.002–3.00) | ? | ? | Xenoestrogen |
| Naringenin | – | 0.0054 (<0.001–0.01) | 0.15 (0.11–0.33) | ? | ? | Xenoestrogen |
| 8-Prenylnaringenin | 8-PN | 4.4 | ? | ? | ? | Xenoestrogen |
| Quercetin | – | <0.001–0.01 | 0.002–0.040 | ? | ? | Xenoestrogen |
| Ipriflavone | – | <0.01 | <0.01 | ? | ? | Xenoestrogen |
| Miroestrol | – | 0.39 | ? | ? | ? | Xenoestrogen |
| Deoxymiroestrol | – | 2.0 | ? | ? | ? | Xenoestrogen |
| β-Sitosterol | – | <0.001–0.0875 | <0.001–0.016 | ? | ? | Xenoestrogen |
| Resveratrol | – | <0.001–0.0032 | ? | ? | ? | Xenoestrogen |
| α-Zearalenol | – | 48 (13–52.5) | ? | ? | ? | Xenoestrogen |
| β-Zearalenol | – | 0.6 (0.032–13) | ? | ? | ? | Xenoestrogen |
| Zeranol | α-Zearalanol | 48–111 | ? | ? | ? | Xenoestrogen |
| Taleranol | β-Zearalanol | 16 (13–17.8) | 14 | 0.8 | 0.9 | Xenoestrogen |
| Zearalenone | ZEN | 7.68 (2.04–28) | 9.45 (2.43–31.5) | ? | ? | Xenoestrogen |
| Zearalanone | ZAN | 0.51 | ? | ? | ? | Xenoestrogen |
| Bisphenol A | BPA | 0.0315 (0.008–1.0) | 0.135 (0.002–4.23) | 195 | 35 | Xenoestrogen |
| Endosulfan | EDS | <0.001–<0.01 | <0.01 | ? | ? | Xenoestrogen |
| Kepone | Chlordecone | 0.0069–0.2 | ? | ? | ? | Xenoestrogen |
| o,p'-DDT | – | 0.0073–0.4 | ? | ? | ? | Xenoestrogen |
| p,p'-DDT | – | 0.03 | ? | ? | ? | Xenoestrogen |
| Methoxychlor | p,p'-Dimethoxy-DDT | 0.01 (<0.001–0.02) | 0.01–0.13 | ? | ? | Xenoestrogen |
| HPTE | Hydroxychlor; p,p'-OH-DDT | 1.2–1.7 | ? | ? | ? | Xenoestrogen |
| Testosterone | T; 4-Androstenolone | <0.0001–<0.01 | <0.002–0.040 | >5000 | >5000 | Androgen |
| Dihydrotestosterone | DHT; 5α-Androstanolone | 0.01 (<0.001–0.05) | 0.0059–0.17 | 221–>5000 | 73–1688 | Androgen |
| Nandrolone | 19-Nortestosterone; 19-NT | 0.01 | 0.23 | 765 | 53 | Androgen |
| Dehydroepiandrosterone | DHEA; Prasterone | 0.038 (<0.001–0.04) | 0.019–0.07 | 245–1053 | 163–515 | Androgen |
| 5-Androstenediol | A5; Androstenediol | 6 | 17 | 3.6 | 0.9 | Androgen |
| 4-Androstenediol | – | 0.5 | 0.6 | 23 | 19 | Androgen |
| 4-Androstenedione | A4; Androstenedione | <0.01 | <0.01 | >10000 | >10000 | Androgen |
| 3α-Androstanediol | 3α-Adiol | 0.07 | 0.3 | 260 | 48 | Androgen |
| 3β-Androstanediol | 3β-Adiol | 3 | 7 | 6 | 2 | Androgen |
| Androstanedione | 5α-Androstanedione | <0.01 | <0.01 | >10000 | >10000 | Androgen |
| Etiocholanedione | 5β-Androstanedione | <0.01 | <0.01 | >10000 | >10000 | Androgen |
| Methyltestosterone | 17α-Methyltestosterone | <0.0001 | ? | ? | ? | Androgen |
| Ethinyl-3α-androstanediol | 17α-Ethynyl-3α-adiol | 4.0 | <0.07 | ? | ? | Estrogen |
| Ethinyl-3β-androstanediol | 17α-Ethynyl-3β-adiol | 50 | 5.6 | ? | ? | Estrogen |
| Progesterone | P4; 4-Pregnenedione | <0.001–0.6 | <0.001–0.010 | ? | ? | Progestogen |
| Norethisterone | NET; 17α-Ethynyl-19-NT | 0.085 (0.0015–<0.1) | 0.1 (0.01–0.3) | 152 | 1084 | Progestogen |
| Norethynodrel | 5(10)-Norethisterone | 0.5 (0.3–0.7) | <0.1–0.22 | 14 | 53 | Progestogen |
| Tibolone | 7α-Methylnorethynodrel | 0.5 (0.45–2.0) | 0.2–0.076 | ? | ? | Progestogen |
| Δ$^4$-Tibolone | 7α-Methylnorethisterone | 0.069–<0.1 | 0.027–<0.1 | ? | ? | Progestogen |
| 3α-Hydroxytibolone | – | 2.5 (1.06–5.0) | 0.6–0.8 | ? | ? | Progestogen |
| 3β-Hydroxytibolone | – | 1.6 (0.75–1.9) | 0.070–0.1 | ? | ? | Progestogen |
| Footnotes: $^a$ = (1) Binding affinity values are of the format "median (range)" (# (#–#)), "range" (#–#), or "value" (#) depending on the values available. The full sets of values within the ranges can be found in the Wiki code. (2) Binding affinities were determined via displacement studies in a variety of in-vitro systems with labeled estradiol and human ERα and ERβ proteins (except the ERβ values from Kuiper et al. (1997), which are rat ERβ). Sources: See template page. |||||||

### Closely related compounds

Estrogens closely related to the stilbestrols include paroxypropione (a metabolite of diethylstilbestrol) and the anise and fennel-derived compounds anol, dianol, anethole, dianethole, and photoanethole (from which the stilbestrol estrogens were actually originally derived). The triphenylethylene group of estrogenic drugs that includes triphenylethylene itself, estrobin, chlorotrianisene, broparestrol, ethamoxytriphetol, clomifene, tamoxifen, and more recently developed derivatives is also very closely related structurally to the stilbestrols.
Resveratrol is a stilbenoid with estrogenic properties that is not technically a stilbestrol derivative (it is 3,4',5-stilbenetriol).

## Occupational exposure

Occupational exposure to stilbestrol has resulted in gynaecomastia in workers.