17alphaethinyl

17alphaethinyl refers to a chemical functional group, specifically an ethinyl group (-C≡CH) attached to the 17th carbon atom of a steroid nucleus in the alpha (α) position. This specific structural modification is a common feature in many synthetic steroid hormones, particularly oral contraceptives and hormone replacement therapy drugs.

The introduction of the ethinyl group at the 17α position significantly alters the pharmacological properties of the parent steroid. It increases the oral bioavailability of the steroid by making it more resistant to metabolism in the liver. Without this modification, many steroids would be rapidly broken down in the digestive system and liver, rendering them ineffective when taken orally. The ethinyl group sterically hinders the enzymatic degradation of the steroid, allowing it to reach the bloodstream and exert its intended effects.

This structural change is crucial in the development of synthetic progestins like ethinylestradiol and mestranol, which are widely used in birth control pills. It is also found in other synthetic steroids with various therapeutic applications, including anabolic steroids and corticosteroids. The presence of the 17αethinyl group is a key factor in determining a steroid's potency, duration of action, and route of administration.