# 30.7: Prostaglandins

Some of the most recent and exciting developments in the field of natural products are related to the compounds known as prostaglandins. All are oxygenated unsaturated derivatives of prostanoic acid, which is a $$\ce{C_{20}}$$ fatty acid in which there is a cyclopentane ring formed by connecting the $$\ce{C_8}$$ and $$\ce{C_{12}}$$ positions:

There are two main types of prostaglandins that differ in the oxygen function at $$\ce{C_9}$$, which is a carbonyl in Series E (PGE) and hydroxyl in Series F (PGF). Examples follow:

Prostaglandins are found in low concentrations distributed in a large number of organs, tissues, and body fluids of mammals. They exhibit a broad spectrum of physiological activity and are remarkably potent. Their precise biological role is not entirely clear, but they are known to induce strong contractions of smooth muscle tissue (lungs, uterus) and to lower blood pressure and sodium levels. Prostaglandins also have been implicated in the control of pituitary hormones released from the hypothalamus, and in the incidence of "pain" as a response to fever and inflammation. In fact, the analgesic property of aspirin possibly may result from the inhibition of prostaglandin biosynthesis. Although prostaglandins are not yet in extensive clinical use, their wide-ranging physiological effects hold promise that they will become useful drugs for the treatment of high blood pressure, thrombosis, respiratory disease, hypertension, ulcers, and in the regulation of fertility in both men and women.

A number of brilliant total syntheses of natural prostaglandins have been developed and these also have provided a number of interesting prostaglandin analogs. The biosynthesis of prostaglandins proceeds by oxygenation at $$\ce{C_{11}}$$ of unsaturated fatty acids. This is followed by cyclization (probably as the result of a radical addition mechanism) to a bicyclic peroxide. Cleavage of the peroxide ring leads to prostaglandins: