17alpha

17alpha is a designation that can refer to several different scientific concepts, most commonly within the fields of chemistry and steroidology. In organic chemistry, it refers to a specific stereochemical configuration at the 17th carbon atom of a molecule, particularly when that molecule possesses a steroid nucleus. The 'alpha' (α) designation indicates that a substituent at the 17th position is oriented below the plane of the steroid ring system. This stereochemistry is crucial in determining the biological activity and pharmacological properties of many steroid compounds.

For example, in the context of hormones and synthetic steroids, 17alpha-hydroxyprogesterone is a key intermediate in the synthesis of various steroid hormones. Similarly, 17alpha-ethinylestradiol, a synthetic estrogen, is commonly used in oral contraceptives and hormone replacement therapy. The precise arrangement of atoms around the 17th carbon can drastically alter how a molecule interacts with biological receptors and enzymes. Therefore, distinguishing between 17alpha and 17beta isomers is fundamental in understanding steroid chemistry and pharmacology. The 'beta' (β) designation, conversely, indicates a substituent oriented above the plane of the steroid ring system.