August 06, 2018
I was a pioneer in natural product synthesis.
What molecule am I?

Equilenin is a steroidal estrogen originally isolated from the urine of pregnant mares. It was discovered by French researchers A. Girard and co-workers in 1932. The naturally occurring form is the (+)-isomer shown here. It should not be confused with equilin, in which the B ring of equilenin is monohydrogenated.

Among equilenin’s claims to fame is that it was the first complex natural product to be totally synthesized in the laboratory. The feat was accomplished in 1939 by W. E. Bachmann, Wayne Cole, and A. L. Wilds at the University of Michigan (Ann Arbor). The next year, the trio followed up with the total synthesis of the three non-natural stereoisomers of equilenin.

Equilenin, equilin, and several other conjugated equine estrogens (CEEs) are the components of Premarin*, a drug introduced by Wyeth (Philadelphia; now part of Pfizer) in 1941–42. Premarin is a hormone therapy primarily used to treat hot flashes, vaginal burning and dryness experienced by postmenopausal women who have undergone hysterectomies. But Premarin’s many adverse side effects caused it to be replaced by estradiol (Molecule of the Week for November 4, 2013) in some parts of the world.

CEEs are also used to treat some cancers; but ironically, equilenin and other CEEs are also suspected of causing cancer.

*From pregnant mare urine.

Equilenin fast facts

CAS Reg. No. 517-09-9
Molar mass 266.33 g/mol
Empirical formula C18H18O2
Appearance Pale beige crystals or powder
Melting point

258–259 ºC

Water solubility ≈1.5 mg/L

Equilenin hazard information

GHS classification**: carcinogenicity, category 2
H351— Suspected of causing cancer Chemical Safety Warning

**Globally Harmonized System of Classification and Labeling of Chemicals. Explanation of pictograms.

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