Organic Chemistry

1
Organic Chemistry
William H. Brown Christopher S. Foote
2
Lipids

• Chapter 26

3
Lipids

• Lipids a heterogeneous class of naturally
  occurring organic compounds classified together
  on the basis of common solubility properties
• they are insoluble in water but soluble in
  aprotic organic solvents, including diethyl
  ether, methylene chloride, and acetone
• Lipids include
• triglycerides, phospholipids, prostaglandins,
  prostacyclins, and fat-soluble vitamins
• cholesterol, steroid hormones, and bile acids

4
Triglycerides

• Triglyceride an ester of glycerol with three
  fatty acids

5
Fatty Acids

• Fatty acid an unbranched chain carboxylic acid
  derived from hydrolysis of animal fats, vegetable
  oils, or membrane phospholipids
• nearly all have an even number of carbon atoms,
  most between 12 and 20, in an unbranched chain
• the three most abundant are palmitic (160),
  stearic acid (180), and oleic acid (181)
• in most unsaturated fatty acids, the cis isomer
  predominates the trans isomer is rare
• unsaturated fatty acids have lower melting points
  than their saturated counterparts the greater
  the degree of unsaturation, the lower the melting
  point

6
(No Transcript)
7
Triglycerides

• Physical properties depend on the fatty acid
  components
• melting point increases as the number of carbons
  in its hydrocarbon chains increases and as the
  number of double bonds decreases
• triglycerides rich in unsaturated fatty acids are
  generally liquid at room temperature and are
  called oils
• triglycerides rich in saturated fatty acids are
  generally semisolids or solids at room
  temperature and are called fats

8
Triglycerides

• The lower melting points of triglycerides rich in
  unsaturated fatty acids are related to
  differences in their three-dimensional shape
• hydrocarbon chains of saturated fatty acids can
  lie parallel with strong dispersion forces
  between their chains they pack into
  well-ordered, compact crystalline forms and melt
  above room temperature
• because of the cis configuration of the double
  bonds in unsaturated fatty acids, their
  hydrocarbon chains have a less ordered structure
  and dispersion forces between them are weaker
  these triglycerides have melting points below
  room temperature

9
Soaps and Detergents

• Natural soaps are prepared by boiling lard or
  other animal fat with NaOH, in a reaction called
  saponification (Latin, sapo, soap)

10
Soaps and Detergents

• Soaps clean by acting as emulsifying agents
• their long hydrophobic hydrocarbon chains are
  insoluble in water and tend to cluster in such a
  way as to minimize their contact with water
• their polar hydrophilic carboxylate groups, on
  the other hand, tend to remain in contact with
  the surrounding water molecules
• driven by these two forces, soap molecules
  spontaneously cluster into micelles

11
Soaps and Detergents

• micelle a spherical arrangement of organic
  molecules in water clustered so that their
  hydrophobic parts are buried inside the sphere
  and their hydrophilic parts are on the surface of
  the sphere and in contact with water
• when soap is mixed with water-insoluble grease,
  oil, and fats, the nonpolar parts of the soap
  micelles dissolve these nonpolar dirt molecules
  and they are carried away in the polar wash water

12
Soaps and Detergents

• Soaps form water-insoluble salts when used in
  water containing Ca(II), Mg(II), and Fe(III) ions
  (hard water)

13
Synthetic Detergents

• The design criteria for a good detergent are
• a long hydrocarbon tail of 12 to 20 carbons
• a polar head group that does not form insoluble
  salts with Ca(II), Mg(II), or Fe(III) ions
• The most widely used synthetic detergents are the
  linear alkylbenzenesulfonates (LAS)

14
Soaps and Detergents

• Also added to detergent preparations are
• foam stabilizers
• bleaches
• optical brighteners

15
Prostaglandins

• Prostaglandins a family of compounds that have
  the 20-carbon skeleton of prostanoic acid

16
Prostaglandins

• Prostaglandins are not stored in tissues as such,
  but are synthesized from membrane-bound 20-carbon
  polyunsaturated fatty acids in response to
  specific physiological triggers
• one such polyunsaturated fatty acid is
  arachidonic acid

17
Prostaglandins

• among the prostaglandins synthesized
  biochemically from arachidonic acid are

18
Prostaglandins

• Research on the involvement of PGs in
  reproductive physiology has produced several
  clinically useful derivatives
• 15-methyl-PGF2? is used as a therapeutic
  abortifacient

19
Prostaglandins

• the PGE1 analog, misoprostol, is used to prevent
  the ulceration associated with the use of
  aspirin-like NSAIDs

20
Eicosanoids

• The prostaglandins are members of an even larger
  family of compounds called eicosanoids, all of
  which contain 20 carbons and are derived from
  polyunsaturated fatty acids

21
Eicosanoids

• Leukotrienes are found primarily in white blood
  cells. One function is constriction of smooth
  muscles, especially those of the lungs

22
Steroids

• Steroids a group of plant and animal lipids that
  have this tetracyclic ring structure
• The features common to the ring system of most
  naturally occurring steroids are illustrated on
  the next screen

23
Steroids

• the fusion of rings is trans and each atom or
  group at a ring junction is axial
• the pattern of atoms or groups along the ring
  junctions is nearly always trans-anti-trans-anti-t
  rans
• the steroid system is nearly flat and quite rigid
• most have have axial methyl groups at C-10 and
  C-13

24
Cholesterol
25
Androgens

• Androgens - male sex hormones
• synthesized in the testes
• responsible for the development of male secondary
  sex characteristics

26
Anabolic Steroids

• Among the synthetic anabolic steroids are

27
Estrogens

• Estrogens - female sex hormones
• synthesized in the ovaries
• responsible for the development of female
  secondary sex characteristics and control of the
  menstrual cycle

28
Synthetic Estrogens

• Progesterone-like analogs are used in oral
  contraceptives

29
Glucorticoid Hormones

• synthesized in the adrenal cortex
• regulate metabolism of carbohydrates
• decrease inflammation
• involved in the reaction to stress

30
Mineralocorticoid Horm.

• synthesized in the adrenal cortex
• regulate blood pressure and volume by stimulating
  the kidneys to absorb Na, Cl-, and HCO3-

31
Bile Acids

• Synthesized in the liver, stored in the
  gallbladder, and secreted into the intestine
  where their function is emulsify dietary fats and
  aid in their absorption and digestion

32
Biosynthesis of Steroids

• The building block from which all carbon atoms of
  steroids are derived is the two carbon acetyl
  group of acetyl-CoA
• Stage 1 synthesis of isopentenyl pyrophosphate
  from three molecules of acetyl-CoA (Sect 19.4)
• Stage 2 synthesis of cholesterol
• Stage 3 conversion of cholesterol to other
  steroids

33
(No Transcript)
34
Phospholipids

• Phospholipids are the second most abundant group
  of naturally occurring lipids
• they are found almost exclusively in plant and
  animal membranes, which typically consist of 40
  -50 phospholipids and 50 - 60 proteins
• the most abundant phospholipids are derived from
  phosphatidic acid, a molecule in which glycerol
  is esterified with two molecules of fatty acid
  and one of phosphoric acid
• the three most abundant fatty acids in
  phosphatidic acids are palmitic acid (160),
  stearic acid (180), and oleic acid (181)

35
Phospholipids

• A phosphatidic acid
• further esterification with a low-molecular
  weight alcohol gives a phospholipid
• among the most common of these low-molecular-weigh
  t alcohols are

36
Phospholipids

• among the most common of these low-molecular-weigh
  t alcohols are

37
Phospholipids

• A lecithin
• in aqueous solution, phospholipids spontaneously
  form into a lipid bilayer, with a back-to-back
  arrangement of lipid monolayers

38
Biological Membranes

• Fluid mosaic model a biological membrane
  consists of a phospholipid bilayer with proteins,
  carbohydrates, and other lipids embedded on the
  surface and in the bilayer
• fluid signifies that the protein components of
  membranes float in the bilayer and can move
  freely along the plane of the membrane
• mosaic signifies that the various components of
  the membrane exist side by side, as discrete
  units rather than combining to form new molecules
  and ions

39
Fat-Soluble Vitamins

• Vitamins are divided into two broad classes on
  the basis of their solubility
• those that are fat soluble, and hence classified
  as lipids
• those that are water soluble
• The fat-soluble vitamins include A, D, E, and K

40
Vitamin A

• occurs only in the animal world
• found in the plant world in the form of a
  provitamin in a group of pigments called carotenes

41
Vitamin A

• The best understood role of Vitamin A is its
  participation in the visual cycle in rod cells
• the active molecule is retinal (vitamin A
  aldehyde), which forms an imine with an -NH2
  group of the protein opsin to form the visual
  pigment called rhodopsin
• the primary chemical event of vision in rod cells
  is absorption of light by rhodopsin followed by
  isomerization of the 11-cis double bond to the
  11-trans configuration

42
Vitamin A
43
Vitamin D

• A group of structurally related compounds that
  play a role in the regulation of calcium and
  phosphorus metabolism
• the most abundant form in the circulatory system
  is vitamin D3

44
Vitamin E

• Vitamin E is a group of compounds of similar
  structure, the most active of which is
  ?-tocopherol
• In the body, vitamin E functions as an
  antioxidant it traps peroxy radicals of the type
  HOO and ROO formed as a result of oxidation by
  O2 of unsaturated hydrocarbon chains in membrane
  phospholipids

45
Vitamin K

• The name of this vitamin comes from the German
  word Koagulation, signifying its important role
  in the blood-clotting process

46
Prob 26.12

• Account for the detergent properties of each
  compound.

47
Prob 26.15

• Palmitic acid, CH3(CH2)14COOH, is used to
  prepare the hydrocarbon portions of these
  surface-acting germicides and fungicides. Show
  how to convert palmitic acid to
  1-chlorohexadecane (cetyl chloride), and to
  N,N-dimethylhexadecanamine.

48
Prob 26.16

• Calculate the number of grams of epoxyalcohol
  that can be obtained from 100 g of racemic
  epoxyester by this stereospecific
  enzyme-catalyzed hydrolysis.

49
Prob 26.18

• Compare the structural formulas of unoprostone
  and PGF2a.

50
Prob 26.19

• On this and the next two screens are the steps
  in the laboratory synthesis of doxaprost, an
  orally active bronchodilator. Propose reagents to
  bring about each step. Note that the bottom
  reactions on each screen are repeated at the top
  of the following screen.

51
Prob 26.19 (contd)

• Doxoprost (reactions 3 and 4 are repeated here)

52
Prob 26.19 (contd)

• Doxoprost

53
Prob 26.24

• Draw a stereorepresentation of cortisol showing
  the conformation of the five-membered ring and
  each six-membered ring.

54
Prob 26.25

• Knowing what you do about the requirement for
  trans-coplanar ring opening of epoxide rings,
  draw the structural formula of the product formed
  by treating each epoxide with LiAlH4.

55
Prob 26.31

• State the number of cis,trans isomers possible
  for vitamin A.

56

• Lipids

End Chapter 26