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Transcript of 17 17-1 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Introduction to Organic...
1717
17-1Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Introduction to Introduction to Organic Organic
ChemistryChemistry2 ed2 ed
William H. BrownWilliam H. Brown
1717
17-2Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
LipidsLipids
Chapter 17Chapter 17
1717
17-3Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
LipidsLipids• LipidsLipids: a heterogeneous class of naturally
occurring organic compounds classified together on the basis of common solubility properties• insoluble in water• soluble in aprotic organic solvents including diethyl
ether, methylene chloride, and acetone
• Lipids include• triglycerides, phospholipids, prostaglandins, and fat-
soluble vitamins• cholesterol, steroid hormones, and bile acids
1717
17-4Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
TriglyceridesTriglycerides• TriglycerideTriglyceride: an ester of glycerol with three fatty
acids
A triacylglycerol
(a triglyceride)
C H2
O - C R
O
O
O
C H2
O - C R ' '
1 . N a O H , H2
O
2 . H C l , H2
O
C H2
O H
C H2
O H
1,2,3-Propanetriol
(Glycerol, glycerin)
+
R C O2
H
R ' C O2
H
R ' ' C O2
H
Fatty acids
H O C H
R ' C O - C H
1717
17-5Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Fatty AcidsFatty Acids• Fatty acidFatty acid: a long, unbranched chain carboxylic
acid, most commonly of 12 - 20 carbons, derived from hydrolysis of animal fats, vegetable oils, or the phospholipids of biological membranes
• In the shorthand notation for fatty acids• the number of carbons and the number of double
bonds in the chain are shown by two numbers, separated by a colon
1717
17-6Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Fatty AcidsFatty Acids
20:4
18:3
18:2
18:1
16:1
20:0
18:0
16:0
14:0
12:0
Carbon Atoms/
Double Bonds
mp
(°C)
Common
Name
-49
-11
-5
16
1
77
70
63
58
44
arachidonic acid
linolenic acid
linoleic acid
oleic acid
palmitoleic acid
arachidic acid
stearic acid
palmitic acid
myristic acid
lauric acid
1717
17-7Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Fatty AcidsFatty Acids• Among the fatty acids most abundant in plants
and animals• nearly all have an even number of carbon atoms, most
between 12 and 20, in an unbranched chain• the three most abundant are palmitic (16:0), stearic acid
(18:0), and oleic acid (18:1)• 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
1717
17-8Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Fatty AcidsFatty Acids• Stearic and linolenic acids
1717
17-9Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
TriglyceridesTriglycerides• Physical properties of triglycerides depend on
their fatty acid components• melting point increases as the number of carbons in
their 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 oilsoils
• triglycerides rich in saturated fatty acids are generally semisolids or solids at room temperature and are called fatsfats
• The lower melting points of triglycerides rich in unsaturated fatty acids are related to differences in their three-dimensional shape
1717
17-10Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
TriglyceridesTriglycerides• A saturated triglyceride
1717
17-11Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
TriglyceridesTriglycerides• Triglycerides rich in saturated fatty acids:
• saturated hydrocarbon chains can lie parallel and there are strong dispersion forces between their chains
• they pack into well-ordered, compact crystalline forms and have melting points above room temperature
• Triglycerides rich in saturated fatty acids:• because of the cis configuration of their double bonds,
their hydrocarbon chains have a less ordered structure• dispersion forces between hydrocarbon chains are
weaker; these triglycerides have melting points below room temperature
1717
17-12Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Soaps and DetergentsSoaps and Detergents• Natural soaps are prepared by boiling lard or
other animal fat with NaOH, in a reaction called saponification (Latin, sapo, soap)
Sodium soaps
1,2,3-Propanetriol
(Glycerol; Glycerin)
+
saponification+
O
C H O H
C H2
O H
C H2
O H
3 N a O H
3 R C O-
N a+
A triacylglycerol
(a triglyceride)
C H2
O - C R
O
O
O
C H2
O - C R
R C O - C H
1717
17-13Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Soaps and DetergentsSoaps and Detergents• Soaps clean by acting as emulsifying agents
• the long hydrophobic hydrocarbon chains of soaps are insoluble in water and tend to cluster in such a way as to minimize their contact with water
• the polar hydrophilic carboxylate groups tend to remain in contact with the surrounding water molecules
• driven by these two forces, soap molecules spontaneously cluster into micelles
1717
17-14Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Soaps and DetergentsSoaps and Detergents• MicelleMicelle: 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 fat stains, the nonpolar parts of the soap micelles “dissolve” nonpolar dirt molecules and they are carried away in the polar wash water
1717
17-15Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Soaps and DetergentsSoaps and Detergents• Soaps form water-insoluble salts when used in
water containing Ca(II), Mg(II), and Fe(III) ions (hard waterhard water)
+
+
A sodium soap
(soluble in water as micelles)
Calcium salt of a fatty acid
(insoluble in water)
2 C H3
( C H2
)1 4
C O2
- N a
+C a
2 +
[ C H3
( C H2
)1 4
C O2
-]
2C a
2 +2 N a
+
1717
17-16Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Synthetic DetergentsSynthetic 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 alkylbenzene sulfonates (LAS)
1717
17-17Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Soaps and DetergentsSoaps and Detergents
• Also added to detergent preparations are• foam stabilizers• bleaches• optical brighteners
Dodecylbenzene
Sodium 4-dodecylbenzenesulfonate
(an anionic detergent)
C H3
( C H2
)1 0
C H2
C H3
( C H2
)1 0
C H2
S O3
- N a
+
1 . H2
S O4
2 . N a O H
1717
17-18Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
ProstaglandinsProstaglandins• ProstaglandinsProstaglandins: a family of compounds that have
the 20-carbon skeleton of prostanoic acid
Prostanoic acid
19
2018
17
16
15
14
13
7
89
10
1112
6
5
4
3
2
1
CO2
H
1717
17-19Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
ProstaglandinsProstaglandins• 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
Arachidonic acid
1514
89
11 12
6 5
CO 2 H
1717
17-20Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
ProstaglandinsProstaglandins• among the prostaglandins synthesized from
arachidonic acid are
15
9
11
PGF2 α
C O 2 H
H O
H O
H O H
PGE2
11
9
15
H O
C O2
H
H O H
O
1717
17-21Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
ProstaglandinsProstaglandins• Research on the involvement of PGs in
reproductive physiology has produced several clinically useful derivatives• 15-Methyl-PGF2α is used as a therapeutic abortifacient
15
9
11
15- Methyl-PGF2 α
extra methyl group
-15at carbon
CO 2 H
HO
HO
HO CH 3
1717
17-22Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
ProstaglandinsProstaglandins• the PGE1 analog, misoprostol, is used for prevention of
ulceration associated with the use of aspirin-like NSAIDs
1615
Misoprostol
PGE 1
1516
CO2
CH3
HO
O
HO
CH3
HO HHO
O
CO2
H
1717
17-23Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
SteroidsSteroids• SteroidsSteroids: a group of plant and animal lipids that
have this tetracyclic ring structure
A B
C D
1717
17-24Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Common FeaturesCommon Features
• the fusion of rings is trans and each atom or group of atoms at a ring junction is axial
• the pattern of atoms or groups of atoms along the ring junctions is nearly always trans-anti-trans-anti-trans
• the steroid system is nearly flat and quite rigid• many have axial methyl groups at C-10 and C-13
H
CH3
H
H
CH3
H
1717
17-25Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
CholesterolCholesterol
H3
C
HO
H3
C
H H
H
1717
17-26Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
AndrogensAndrogens• Androgens - male sex hormones
• synthesized in the testes• responsible for the development of male secondary sex
characteristics
AndrosteroneTestosterone
O
H
OH
H
H 3 C H
H
H3
C H3
C
H
HH 3 C
H
O
HO
1717
17-27Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Anabolic SteroidsAnabolic Steroids• Among the synthetic anabolic steroids are
Stanozolol
Methandrostenolone
17
2
1
A
O
C H3
O H
H
H3
C H
H
H3
C
H3
C
H
HH3
C
H
O H
C H3
N
N
HH
1717
17-28Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
EstrogensEstrogens• Estrogens - female sex hormones
• synthesized in the ovaries• responsible for the development of female secondary
sex characteristics and control of the menstrual cycle
Progesterone Estrone
H3
C
H
HH3
C
H
C=O
H
O
CH3
O
HO
H
H
H
H3
C
1717
17-29Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Synthetic EstrogensSynthetic Estrogens• Progesterone-like analogs are used in oral
contraceptives"Nor" refers to the absence
of a methyl group here.
It is present in ethindrone
Norethindrone
H3
C
H
HH
O
H
H OC C H
1717
17-30Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Glucorticoid HormonesGlucorticoid Hormones• synthesized in the adrenal cortex• regulate metabolism of carbohydrates• decrease inflammation• involved in the reaction to stress
CortisolCortisone
C=O
CH2
OH
O
OH
H
H3
C H
H
H3
C
O HO
H3
C
H
HH3
C
H
C=O
OH
O
CH2
OH
1717
17-31Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Mineralocorticoid Horm.Mineralocorticoid Horm.• synthesized in the adrenal cortex• regulates blood pressure and volume by stimulating the
kidneys to absorb Na+ , Cl-, and HCO3-
Aldosterone
C = O
C H2
O H
O
H
H3
C H
H
C HO
O H
1717
17-32Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Bile AcidsBile 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
H3
C
HO
H3
C
CO2
H
H H
H
HOH
Cholic acid
1717
17-33Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Biosynthesis of SteroidsBiosynthesis of Steroids• all carbon atoms of cholesterol are derived from the
two carbon acetyl group of acetyl-CoA• cholesterol is, in turn, the starting material for the
synthesis of these classes of compounds
Cholesterol
bile acids
(e.g., cholic acid)
sex hormones
(e.g., testosterone and estrone)
mineralocorticoid homones
(e.g., aldosterone)
glucocorticoid hormones
(e.g., cortisone)
1717
17-34Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
PhospholipidsPhospholipids• 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 (16:0), stearic acid (18:0), and oleic acid (18:1)
1717
17-35Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
PhospholipidsPhospholipids• A phosphatidic acid
• Further esterification with a low-molecular weight alcohol gives a phospholipid• among the most common of these low-molecular-
weight alcohols are
C H 2
C H
C H2
- O - P - O-
O
O
O
O
O
O-
glycerol
palmitic acid
stearic acid
1717
17-36Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
PhospholipidsPhospholipidsName and Formula Name of Phospholipid
ethanolamine
+choline
phosphatidylcholine
(lecithin)
phosphatidylethanolamine
(cephalin)
serine
phosphatidylserine
inositol
phosphatidylinositol
N H 3
+
H O
H OO H
O H
O HH O
H O C H 2 C H C O 2
-
H O C H 2 C H 2 N ( C H 3 ) 3
H O C H 2 C H 2 N H 2
1717
17-37Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
PhospholipidsPhospholipids• A lecithin
• in aqueous solution, phospholipids spontaneously form into a lipid bilayer, with a back-to-back arrangement of lipid monolayers
C H2
C H
C H2
O
O
O
O
O P O C H2
C H2
N ( C H3
)3
O
O-
+
palmitic acid
stearic acid
glycerol
choline
1717
17-38Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
A LecithinA Lecithin
1717
17-39Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Biological MembranesBiological Membranes• Fluid mosaic modelFluid mosaic model: a biological membrane
consists of a phospholipid bilayer with proteins, carbohydrates, and other lipids embedded on the surface and in the bilayer• fluidfluid signifies that the protein components of
membranes “float”in the bilayer and can move freely along the plane of the membrane
• mosaicmosaic signifies that the various components of the membrane exist side-by-side, as discrete units rather than combining to form new molecules and ions
1717
17-40Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Fat-Soluble VitaminsFat-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
1717
17-41Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Vitamin AVitamin A• Vitamin A, or retinol, occurs only in the animal
world
• Vitamin A is found in the plant world in the form of a provitamin in a group of pigments called carotenes (tetraterpenes)• enzyme-catalyzed cleavage of -carotene followed by
reduction gives two molecules of vitamin A
CH3
CH3
CH3
CH3
CH3
CH2
OH
Retinol (Vitamin A)
1717
17-42Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Vitamin AVitamin Asite of
cleavage
- Carotene
enzyme-catalyzed cleavage
and reduction in the liver
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
H3
C
H3
C
CH3
CH3
CH3
CH3
CH2
OH
Retinol (Vitamin A)
1717
17-43Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Vitamin AVitamin 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
1717
17-44Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Vitamin AVitamin A
CH3
CH3
CH3
CH 3CH 3
CH=N-opsin11
12
CH3
CH3
CH3
H3
C
CH3
CH=N-opsin
11
12
11-12 cis configuration
light
1717
17-45Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Vitamin DVitamin 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
V itamin D3
HO
1717
17-46Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Vitamin EVitamin E• Vitamin E: a group of compounds of similar
structure• the most active is α-tocopherol
F our isoprene units, joined
head-to-tail, beginning here
and ending at the aromatic ring
V itamin E ( α - )Tocopherol
H3
C
H3
C
H3
C
C H3
O H
OC H
3C H
3
C H3
C H3
1717
17-47Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Vitamin EVitamin E• 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
1717
17-48Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Vitamin KVitamin K• The name of this vitamin comes from the German
word Koagulation, signifying its important role in the blood-clotting process
Vitamin K1
isoprene units
2
O
O
CH3
O
O
CH3
2
O
O
CH3
O
O
CH3
Menadione
(a synthetic
vitamin K analog)
1717
17-49Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
LipidsLipids
End Chapter 17End Chapter 17