Organic Chemistry 6 th Edition Paula Yurkanis Bruice

1. Chapter 27 The Organic Chemistry of Lipids Organic Chemistry 6th Edition Paula Yurkanis Bruice

2. Lipids are soluble in nonpolar organic compounds and have a variety of structures and functions:

3. Common Naturally Occurring Fatty Acids

4. Fatty acids, a major group of lipids, are carboxylic • acids with long hydrocarbon chains. • Polyunsaturated fatty acids have more than one double bond. • 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.

5. Unsaturated fatty acids have lower melting points than saturated fatty acids

6. Waxes Are High-Molecular-Weight Esters

7. Fats and Oils • The three OH groups of glycerol are esterified with fatty acids. • A simple triacylglycerol has three identical fatty acid components. • A mixed triacylglycerol has two or three different fatty acid components.

8. Fats are triacylglycerols existing as solid or semisolid state at room temperature:

9. Oils are liquid triacylglycerols:

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.

11. Oxidation of Polyunsaturated Fats and Oils by O2

12. Phosphoacylglycerols • They are the major components of cell membranes. • The terminal OH group of glycerol is esterified with • phosphoric acid.

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.

14. Phosphoacylglycerols form membranes by arranging themselves into a lipid bilayer:

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

16. Two of the Most Common Kinds of Sphingolipids

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

18. Examples of prostaglandins and physiological processes they regulate: • Blood pressure • Clotting • Fever • Pain • Labor • Sleep–wake cycle

19. Prostaglandin endoperoxide synthase catalyzes the conversion of arachidonic acid to PGH2. • 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.

21. Aspirin (acetylsalicyclic acid) inhibits cyclooxygenase activity:

22. Other anti-inflammatory drugs also compete with arachidonic acid or the peroxy radical for the enzyme’s binding site:

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

24. The Isoprene Rule

26. Recognizing the Isoprene Subunit • Zingiberene, oil of ginger • Has three isoprene units

27. Squalene, a triterpene, is a precursor of steroid molecules:

28. Lycopene and b-carotene are tetraterpenes called carotenoids:

29. Vitamin A Is a Terpene

31. Isopentenyl pyrophosphate is the starting point for biosynthesis of terpenes:

32. The Conversion of Mevalonic Acid into Mevalonyl Phosphate an SN2 reaction a second SN2 Review Sections 26.2 and 26.3

33. Isoprene Biosynthesis: Claisen Condensation • Starred carbon can be 14C • Claisen condensation joins two acetates

34. Isoprene Biosynthesis: Second Claisen Condensation

35. Isoprene Biosynthesis: Leaving Group Elaboration

36. Isoprene Biosynthesis: Elimination and Isomerization Isopentenyl pyrophosphate Dimethylallyl pyrophosphate

37. Both isopentyl pyrophosphate and dimethylallyl pyrophosphate are needed for the biosynthesis of terpenes

38. Terpene Biosynthesis Formation of geranyl pyrophosphate:

39. Geranyl Pyrophosphate Formation with 14C-Labels

40. Many monoterpenes can be synthesized from geranyl pyrophosphate:

41. Formation of Farnesyl Pyrophosphate

42. Formation of Squalene, the Precursor of Cholesterol

43. Steroids • Steroids are nonpolar compounds and are lipids. • Hormones are chemical messengers. • Many hormones are steroids. • Steroids contain a tetracyclic ring system.

44. Structural Features of Steroids

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

46. The A and B rings are also trans fused in most naturally occurring steroids: • Substituents on the same side of the steroid ring system as the angular methyl groups are b-substituents. • Thoseon the opposite side of the plane of the ring • system are a-substituents.

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

48. Examples of Steroids

50. Examples of Synthetic Steroids