Steroids are a class of naturally occurring organic substances that are of great importance in biology, medicine, and chemistry. The steroid group includes all the sex hormones, adrenal cortical hormones, bile acids, and sterols of vertebrates, the molting hormones of insects, and many other physiologically active substances of animals and plants. Among the synthetic steroids of therapeutic importance are a large number of anti-inflammatory agents, anabolic (growth stimulating) agents, and oral contraceptives. .
All steroids are related to a characteristic molecular structure composed of 17 carbon atoms arranged in four rings conventionally denoted by the letters A, B, C, and D. These four carbon rings are then additionally bonded to 28 hydrogen atoms. This parent structure, named gonane and often referred to as the steroid nucleus, may be modified in a practically unlimited number of ways by removal, replacement, or addition of a few atoms at a time. Hundreds of steroids have been isolated from plants and animals, and thousands more have been prepared by chemical treatment of natural steroids or by synthesis from simpler compounds.
The hormone estrone is usually manufactured from pregnant mares urine, in which it is present almost entirely as the ethereal sulfate. This is hydrolyzed to estrone by acidification of the urine and heating, after previously covering with a layer of immiscible solvent, such as toluene. Estrogens are extracted from the solvent, and the estrone is separated from the other estrogens.
The most potent natural estrogen is estradiol; the less potent estrogens include estrone, estriol, and other oxygenated phenolic steroids. Some species, notably the Equidae, secrete the less active estrogen equilenin. Synthetic estrogens, such as estranol or mestranol (18), commonly used in oral contraceptives and for other therapeutic purposes, have acetylenic atoms and contain triple bonds between carbon atoms.