26.7 Terpenes: The isoprene Rule 1025 present at this position in the various PGEs. The subscript numerals in their abbreviated names indicate the number of double bonds Prostaglandins are believed to arise from unsaturated Czo-carboxylic acids such as Arachidonic acid gets its arachidonic acid(see Table 26.1). Mammals cannot biosynthesize arachidonic acid name from arachidic acid directly. They obtain linoleic acid (Table 26. 1)from vegetable oils in their diet and extend d Czo fatty at the carbon chain of linoleic acid from 18 to 20 carbons while introducing two more dou- ble bonds. Linoleic acid is said to be an essential fatty acid, forming part of the dietary (Arachis hypogaea)oil requirement of mammals. Animals fed on diets that are deficient in linoleic acid grow poorly and suffer a number of other disorders, some of which are reversed on feeding them vegetable oils rich in linoleic acid and other polyunsaturated fatty acids. One func tion of these substances is to provide the raw materials for prostaglandin biosynthesis PROBLEM 26.6 Arachidonic acid is the biosynthetic precursor to PGE2. The struc. tures of PGE,(see Figure 26.5)and PGE, are identical except that PGE, has one more double bond than PGE. Suggest a reasonable structure for PGE,. Physiological responses to prostaglandins encompass a variety of effects. Some prostaglandins relax bronchial muscle, others contract it. Some stimulate uterine con- tractions and have been used to induce therapeutic abortions. PGE, dilates blood vessel and lowers blood pressure; it inhibits the aggregation of platelets and offers promise as a drug to reduce the formation of blood clots The long-standing question of the mode of action of aspirin has been addressed in terms of its effects on prostaglandin biosynthesis. Prostaglandin biosynthesis is the body's response to tissue damage and is manifested by pain and inflammation at the affected site. Aspirin has been shown to inhibit the activity of an enzyme required for prostaglandin formation. Aspirin reduces pain and inflammation-and probably fever as well-by reducing prostaglandin levels in the body Much of the fundamental work on prostaglandins and related compounds was car ried out by Sune Bergstrom and Bengt Samuelsson of the Karolinska Institute(Sweden) and by Sir John Vane of the Wellcome Foundation( Great Britain). These three shared the Nobel Prize for physiology or medicine in 1982. Bergstrom began his research on prostaglandins because he was interested in the oxidation of fatty acids. That research led to the identification of a whole new class of biochemical mediators prostaglandi research has now revealed that other derivatives of oxidized polyunsaturated fatty acid structurally distinct from the prostaglandins, are also physiologically important. These fatty acid derivatives include, for example, a group of substances known as the leukotrienes, which have been implicated as mediators in immunological processes 26.7 TERPENES: THE ISOPRENE RULE The word"essential"as applied to naturally occurring organic substances can have two different meanings. For example, as used in the previous section with respect to fatty acids, essential means""necessary "Linoleic acid is an"essential"fatty acid; it must be included in the diet in order for animals to grow properly because they lack the ability to biosynthesize it directly. Essential"is also used as the adjective form of the noun "essence " The mixtures of substances that make up the fragrant material of plants are called essential oils because they contain the essence, that is, the odor, of the plant. The study of the composition of essential oils ranks as one of the oldest areas of organic chemical research. Very often, the principal volatile component of an essential oil belongs to a class of chemical sub stances called the terpenes Back Forward Main MenuToc Study Guide ToC Student o MHHE Website26.7 Terpenes: The Isoprene Rule 1025 present at this position in the various PGEs. The subscript numerals in their abbreviated names indicate the number of double bonds. Prostaglandins are believed to arise from unsaturated C20-carboxylic acids such as arachidonic acid (see Table 26.1). Mammals cannot biosynthesize arachidonic acid directly. They obtain linoleic acid (Table 26.1) from vegetable oils in their diet and extend the carbon chain of linoleic acid from 18 to 20 carbons while introducing two more dou￾ble bonds. Linoleic acid is said to be an essential fatty acid, forming part of the dietary requirement of mammals. Animals fed on diets that are deficient in linoleic acid grow poorly and suffer a number of other disorders, some of which are reversed on feeding them vegetable oils rich in linoleic acid and other polyunsaturated fatty acids. One func￾tion of these substances is to provide the raw materials for prostaglandin biosynthesis. PROBLEM 26.6 Arachidonic acid is the biosynthetic precursor to PGE2. The struc￾tures of PGE1 (see Figure 26.5) and PGE2 are identical except that PGE2 has one more double bond than PGE1. Suggest a reasonable structure for PGE2. Physiological responses to prostaglandins encompass a variety of effects. Some prostaglandins relax bronchial muscle, others contract it. Some stimulate uterine con￾tractions and have been used to induce therapeutic abortions. PGE1 dilates blood vessels and lowers blood pressure; it inhibits the aggregation of platelets and offers promise as a drug to reduce the formation of blood clots. The long-standing question of the mode of action of aspirin has been addressed in terms of its effects on prostaglandin biosynthesis. Prostaglandin biosynthesis is the body’s response to tissue damage and is manifested by pain and inflammation at the affected site. Aspirin has been shown to inhibit the activity of an enzyme required for prostaglandin formation. Aspirin reduces pain and inflammation—and probably fever as well—by reducing prostaglandin levels in the body. Much of the fundamental work on prostaglandins and related compounds was car￾ried out by Sune Bergström and Bengt Samuelsson of the Karolinska Institute (Sweden) and by Sir John Vane of the Wellcome Foundation (Great Britain). These three shared the Nobel Prize for physiology or medicine in 1982. Bergström began his research on prostaglandins because he was interested in the oxidation of fatty acids. That research led to the identification of a whole new class of biochemical mediators. Prostaglandin research has now revealed that other derivatives of oxidized polyunsaturated fatty acids, structurally distinct from the prostaglandins, are also physiologically important. These fatty acid derivatives include, for example, a group of substances known as the leukotrienes, which have been implicated as mediators in immunological processes. 26.7 TERPENES: THE ISOPRENE RULE The word “essential” as applied to naturally occurring organic substances can have two different meanings. For example, as used in the previous section with respect to fatty acids, essential means “necessary.” Linoleic acid is an “essential” fatty acid; it must be included in the diet in order for animals to grow properly because they lack the ability to biosynthesize it directly. “Essential” is also used as the adjective form of the noun “essence.” The mixtures of substances that make up the fragrant material of plants are called essential oils because they contain the essence, that is, the odor, of the plant. The study of the composition of essential oils ranks as one of the oldest areas of organic chemical research. Very often, the principal volatile component of an essential oil belongs to a class of chemical sub￾stances called the terpenes. Arachidonic acid gets its name from arachidic acid, the saturated C20 fatty acid isolated from peanut (Arachis hypogaea) oil. Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website