© 2011 Pearson Education, Inc. 1 Organic Chemistry 6 th Edition Paula Yurkanis Bruice Chapter 27 The Organic Chemistry of Lipids

© 2011 Pearson Education, Inc. 2 Lipids are soluble in nonpolar organic compounds and have a variety of structures and functions:

© 2011 Pearson Education, Inc. 3 Common Naturally Occurring Fatty Acids

© 2011 Pearson Education, Inc. 4 The double bonds in naturally occurring fatty acids have the cis configuration. Double bonds in naturally occurring unsaturated fatty acids are separated by one methylene group. Polyunsaturated fatty acids have more than one double bond. Fatty acids, a major group of lipids, are carboxylic acids with long hydrocarbon chains.

© 2011 Pearson Education, Inc. 5 Unsaturated fatty acids have lower melting points than saturated fatty acids

© 2011 Pearson Education, Inc. 6 Waxes Are High-Molecular-Weight Esters

© 2011 Pearson Education, Inc. 7 Fats and Oils A simple triacylglycerol has three identical fatty acid components. A mixed triacylglycerol has two or three different fatty acid components. The three OH groups of glycerol are esterified with fatty acids.

© 2011 Pearson Education, Inc. 8 Fats are triacylglycerols existing as solid or semisolid state at room temperature:

© 2011 Pearson Education, Inc. 9 Oils are liquid triacylglycerols:

© 2011 Pearson Education, Inc. 10 Some or all of the double bonds of polyunsaturated oils can be reduced by catalytic hydrogenation (Section 4.12) Catalytic hydrogenation is used to convert oils to fats (e.g., vegetable oil to margarine). This process also isomerizes double bonds from cis to trans, resulting in unhealthy trans fats.

© 2011 Pearson Education, Inc. 11 Oxidation of Polyunsaturated Fats and Oils by O 2

© 2011 Pearson Education, Inc. 12 Phosphoacylglycerols The terminal OH group of glycerol is esterified with phosphoric acid. They are the major components of cell membranes.

© 2011 Pearson Education, Inc. 13 The most common phosphoacylglycerols in membranes are phosphodiesters. The alcohols most commonly used to form the second ester group are ethanolamine, choline, and serine.

© 2011 Pearson Education, Inc. 14 Phosphoacylglycerols form membranes by arranging themselves into a lipid bilayer:

© 2011 Pearson Education, Inc. 15 Sphingolipids They contain an amino alcohol called sphingosine instead of glycerol: Sphingolipids are the major lipid component in the myelin sheath, the insulator of nerve cells axons

© 2011 Pearson Education, Inc. 16 Two of the Most Common Kinds of Sphingolipids

© 2011 Pearson Education, Inc. 17 Prostaglandins are synthesized from arachidonic acid. They are responsible for regulating a variety of physiological responses. Prostaglandins They are classified using the formula PGX, where X designates the functional groups of the five-membered ring.

© 2011 Pearson Education, Inc. 18 Blood pressure Clotting Fever Pain Labor Sleep–wake cycle Examples of prostaglandins and physiological processes they regulate:

© 2011 Pearson Education, Inc. 19 Prostaglandin endoperoxide synthase catalyzes the conversion of arachidonic acid to PGH 2. There are two forms of this enzyme: production under normal physiological conditions and in response to inflammation. The enzyme has a cyclooxygenase activity and a hydroperoxidase activity.

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© 2011 Pearson Education, Inc. 21 Aspirin (acetylsalicyclic acid) inhibits cyclooxygenase activity:

© 2011 Pearson Education, Inc. 22 Other anti-inflammatory drugs also compete with arachidonic acid or the peroxy radical for the enzyme’s binding site:

© 2011 Pearson Education, Inc. 23 Terpenes contain carbon atoms in multiples of five. They are made by joining five-carbon isoprene units. Terpenes Oxygen-containing terpenes are sometimes called terpenoids. They are a diverse class of lipids.

© 2011 Pearson Education, Inc. 24 The Isoprene Rule

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© 2011 Pearson Education, Inc. 26 Recognizing the Isoprene Subunit Zingiberene, oil of ginger Has three isoprene units

© 2011 Pearson Education, Inc. 27 Squalene, a triterpene, is a precursor of steroid molecules:

© 2011 Pearson Education, Inc. 28 Lycopene and  -carotene are tetraterpenes called carotenoids:

© 2011 Pearson Education, Inc. 29 Vitamin A Is a Terpene

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© 2011 Pearson Education, Inc. 31 Isopentenyl pyrophosphate is the starting point for biosynthesis of terpenes:

© 2011 Pearson Education, Inc. 32 The Conversion of Mevalonic Acid into Mevalonyl Phosphate an S N 2 reaction a second S N 2 Review Sections 26.2 and 26.3

© 2011 Pearson Education, Inc. 33 Isoprene Biosynthesis: Claisen Condensation Starred carbon can be 14 C Claisen condensation joins two acetates

© 2011 Pearson Education, Inc. 34 Isoprene Biosynthesis: Second Claisen Condensation

© 2011 Pearson Education, Inc. 35 Isoprene Biosynthesis: Leaving Group Elaboration

© 2011 Pearson Education, Inc. 36 Isoprene Biosynthesis: Elimination and Isomerization Isopentenyl pyrophosphate Dimethylallyl pyrophosphate

© 2011 Pearson Education, Inc. 37 Both isopentyl pyrophosphate and dimethylallyl pyrophosphate are needed for the biosynthesis of terpenes

© 2011 Pearson Education, Inc. 38 Formation of geranyl pyrophosphate: Terpene Biosynthesis

© 2011 Pearson Education, Inc. 39 Geranyl Pyrophosphate Formation with 14 C-Labels

© 2011 Pearson Education, Inc. 40 Many monoterpenes can be synthesized from geranyl pyrophosphate:

© 2011 Pearson Education, Inc. 41 Formation of Farnesyl Pyrophosphate

© 2011 Pearson Education, Inc. 42 Formation of Squalene, the Precursor of Cholesterol

© 2011 Pearson Education, Inc. 43 Hormones are chemical messengers. Many hormones are steroids. Steroids are nonpolar compounds and are lipids. Steroids Steroids contain a tetracyclic ring system.

© 2011 Pearson Education, Inc. 44 Structural Features of Steroids

© 2011 Pearson Education, Inc. 45 Methyl groups at C-10 and C-13 are called angular methyl groups In steroids, the B, C, and D rings are trans fused:

© 2011 Pearson Education, Inc. 46 Those  on the opposite side of the plane of the ring system are  -substituents. Substituents on the same side of the steroid ring system as the angular methyl groups are  -substituents. The A and B rings are also trans fused in most naturally occurring steroids:

© 2011 Pearson Education, Inc. 47 Cholesterol Is a Steroid The most abundant member of the steroid family in animals The precursor of all other steroids More rigid than other membrane lipids

© 2011 Pearson Education, Inc. 48 Examples of Steroids

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© 2011 Pearson Education, Inc. 50 Examples of Synthetic Steroids