CHAPTER 23 LIPIDS 23.1 INTRODCTION s are compounds of biological origin that dissolve poler solvents. s are defined by the physical operation that we use te them.
Dec 26, 2015
CHAPTER 23 LIPIDS
23.1 INTRODCTION
Lipids are compounds of biological origin that dissolve in nonopoler solvents.
Lipids are defined by the physical operation that we use to isolate them.
Lipids include a variety of structure types, For example
H2C
HC
H2C
O C R
O C R'
O C R''
O
O
O
CH3
OH
CH(CH3)2
CH2OH
CH3 CH3
CH3
CH3
A fat or oil (ÓÍ»òÖ¬£©
Menthol(±¡ ºÉ´¼)
Vitamin A(άÉúËØ A£©
H2C
HC
H2C
O C R
O C R'
O P OCH2CH2N+(CH3)3
O
O
O
O-
H
HH3C
H3C
H
H
H
HO
CH3
Cholesterol (µ¨ ¹Ì ´¼)
lecithin(ÂÑÁ×Ö¬)
23.2 FATTY ACIDS AND TRIACYLGLYCEROLS
Triacylglycerols are the fats and oils of plant or animal origin.
Oils: Triacylglycerols that are liquids at room temperature. Fats: Triacylglycerols that are solids at room temperature.
Same triacylglycerols: all three acyl groups in triacylglycerols are the same. mixed triacylglycerols: the acyl groups in triacylglycerols are different.
Hydrolysis of a fat or oil produced a mixture of fatty acids.
H2C
HC
H2C
O C R
O C R'
O C R''
O
O
O
A fat or oil (ÓÍ»òÖ¬£©
H2C
HC
H2C
OH
OH
OH
+
RCOOH
R'COOH
R''COOH
(1) OH- / H2O, heat
(2) H3O+
Glycerol( ±ûÈý́ ¼)
Fatty acids(Ö¬·¾Ëᣩ
Most of fatty acids have unbrached chains and they have an even number of carbon atoms.
The double bonds in unsaturated fatty acids are all cis and not conjugated. Many naturally occurring fatty acids contain two or three double bonds. Triple bond rarely occur in fatty acids.
Saturated fatty acids have relatively high points and unsaturated fatty acids have relatively low points.
Triacylglycerols made up of large saturated fatty acids have high melting points and are solid in room temperature, vice versa.
23.2A HYDROGENATION OF TRIACYLGLYCEROLS
Solid commercial cooking fats are manufactured by partialhydrogenation of vegetable oils. Completed hydrogenationof the oil is very hard and brittle. One commercial advantageof partial hydrogenation is to give the fat a longer shelf-life.
23.2B BIOLOGICAL FUNCTION OF TRIACYLGLYCEROLS
The primary function of triacylglycerols in animal is as an energy reserve.
All of the saturated triacylglycerols of the body, and some of the unsaturated ones, can be synthesized from carbohydrates andproteins.
23.2C SAPONIFICATION OF TRIACYLGLYCEROLS
Alkaline hydrolysis of triacylglcerols produces glycerol and a mixture of salts of long-chain carboxylic acids.
H2C
HC
H2C
O C R
O C R'
O C R''
O
O
O
H2C
HC
H2C
OH
OH
OH
+
RCOO-Na+
R'COO-Na+
R''COO-Na+
Glycerol( ±ûÈý́ ¼)
Sodium carboxylates (ôÈËáÄÆÑΣ©
+ 3NaOHH2O
These salts of long-chain carboxylic acids are soaps and this saponification reaction is the way most soaps are manufactured.
Soaps are almost completely miscible with water. Soaps micellesin water are usually spherical clusters of carboxylate ions that are dispersed throughout the aqueous phase with their negativelycharged carboxylate groups at the surface and with their nonpolar hydrocarbon chains on the interior.
Thus soap solution are able to separate the dirt particles because their hydrocarbon chains can “dissolve” in the oil layer.
Synthetic detergents function in the same way as soaps; they havelong nonpolar alkane chains with polar groups at the end.
CH3(CH2)nCH2SO2O-Na+ CH3(CH2)nCH2OSO2O-Na+
CH(CH2)nCH2CH3+Na-OO2S
CH3
Sodium alkylbenzenesulfonates (Íé»ù±½»ÇËáÄÆÑΣ©
Sodium alkyl sulfates (Íé»ùÁòËáÄÆÑΣ©
Sodium alkanesulonates (Íé»ù»ÇËáÄÆÑΣ©
Synthesis of detergents offer an advantage over soaps; they function well in “hard” water.
23.2D REACTIONS OF THE CARBOXYL GROUP OF FATTY ACIDS
Fatty acids undergo reactions typical of carboxylic acids.they reactwith LiAlH4 to form alcohols, with alcohols and mineral acid toform esters, with thionyl chloride to form acyl chlorides:
RCH2COOH
(1)LiAlH4, diethyl ether
(2) H2O
CH3OH, H+
SOCl2Pyridine
RCH2CH2OH
RCH2COOCH3
RCH2COCl
23.2E REACTIONS OF THE ALKYL CHAIN OF SATURATED FATTY ACIDS
Fatty acids undergo specific halogenation when they are treatedwith bromine or chlorine in the presence of phosphorus.
RCH2COOH +(1) X2, P4
(2) H2ORCHXCOOH + HX
23.2F REACTIONS OF THE ALKENYL CHAIN OF UNSATURATED FATTY
The double bonds of the carbon chains of fatty acids undergo characteristic alkene addition reactions.
CH3(CH2)nCH=CH(CH2)mCO2H
H2
Ni
Br2CCl4
(1) OsO4(2) NaHSO3
HBr
CH3(CH2)nCH2 CH2(CH2)mCO2H
CH3(CH2)nCHBrCHBr(CH2)mCO2H
CH3(CH2)nCHOH CHOH(CH2)mCO2H
CH3(CH2)nCH2CHBr(CH2)mCO2H
CH3(CH2)nCHBrCH2(CH2)mCO2H+
23.3 TERPENES AND TERPENOIDS
Hydrocarbons known generally as terpenes and oxygen-containingcompounds called terpenoids are the most important constitutentsof essential oils.
Most terpenes have skeletons of 10,15,20 or 30 carbon atoms and are classified in the following way.
10
15
20
30
Monoterpenes
Sesquiterpenes
Diterpenes
Triterpenes
Recognition of the isoprene unit as a component of the structure of terpenes has been a great aid in elucidating their structures.
Many terpenes also have isoprene units linked in rings, and others(terpenoids) contain oxygen.
H2C
H2CCH
CH2
CHC
CH2
CCH3H3C
H2C
H2CCH
CH
C
H2CC
CH
H2C
CH3 CH2
CH
CCH3H3C
CH3
or
or
OH
Limonene(ÄûÃÊÓ;«)
-Pinene(ËÉÝÆ)
Geraniol (Ïã Ò¶́ ¼)
Menthol (±¡ ºÉ´¼)
The carotenes are tetraterpenes. They can be thought of as two diterpenes linked in tail-to-tail fashion.
CH3
CH3
CH3
CH3
H3C
H3C
CH3CH3
CH3H3C
-Carotene(ºú ÂÞ²· ËØ)
CH3
CH3
CH3
CH3
H3C
H3C
CH3CH3
CH3H3C
-Carotene(ºú ÂÞ²· ËØ)
CH3
CH3
CH3
CH3
H3C
H3C
CH3CH3
CH3H3C
-Carotene(ºú ÂÞ²· ËØ)
The catotenes all can be converted to vitamin A by enzymes in the liver.
23.3A NATURAL RUBBER
The isoprene units of natural rubber are all linked in a head-to-tailfashion and all of the bonds are cis.
CH2
H3C H
CH2
H3C
H2C CH2
H
H2C
H3C H
CH2etc etc
Narura rubber(ÌìÈ»Ï𽺣©
Pure rubber is soft and tacky, so it must be vulcanized by heatingwith sulfur. A reaction takes place that produces cross-links between the cis-polyisoprene chains and makes the robber much harder.
23.4 STEROIDS
Steroids are important “biological regulators” that nearly always show dramatic physiological effects when they are administered to living organisms.
23.4A ATRUCTURE AND SYSTEMATIC NOMENCLATURE OF STEROIDS
Steroids are derivatives of the following perhydrocyclopentanophenanthrene ring system
CH3
CH31
2
3
45
6
7
89
10
11
12
13
14 15
1617
18
19
A B
C D
RCH3
CH3
HH
12
3 45
67
8910
1112
13
1415
16
17
1819
A BC D
all ring junctions are trans
In most steroids the B, C and C, D ring junctions are trans. The A, B ring junction may be either cis or trans.
1
2
34
56
7
8910
1112
13
14 1516
17
18
19
A
BC D
A, B ring junctions is cis
RCH3
H
CH3
H
Angular methyl groups: The methyl groups that are attached at points of ring junction
β substituents: other groups that lie on the same general side of the Molecule as the angular methyl groups.
α substituents: groups that lie on the bottom.
When α and β designation are applied to the hydrogen atom at position 5,the ring system in which the A, B ring junction istrans become the 5 α series; and the ring system in which the A, B ring junction is cis becomes the 5 β series.
In systematic nomenclature of the R group at position 17 determines the base name of an individual steroid.
RHH3C
H
H
H
CH3
H
17
18
19
For example:
-H -CH2CH3
-CH(CH3)CH2CH2CH3
Androstane (ÐÛ(çÞ)Íé )
Pregnane (ÔÐÍé )
Cholane (µ¨Íé )
20 21
20 21 22 23 24
CH2CH3HH3C
H
H
H
CH3
H
17
18
19
O
5 -Pregnan-3-one (5 -ÔÐ-3-Íé £©
CH(CH3)(CH2)3CH(CH3)2HH3C
H
H
H
CH3
H
17
18
19
O
5 -Cholest-1-en-3-one(5 -µ¨ -1-Ï©-3-Íé £©
The following two examples illustrate the way these base names are used.
23.4B CHOLESTEROL
Cholesterol can be isolated by extraction of nearly all animal tissues.part of the difficulty in assigning an absolute structure to cholesterol is that cholesterol contains eight tetrahedral. For example:
C
H
HH3C
H3C
H
H
HHO
CH3
H
Cholesterol is known to serve as an intermediate in the biosynthesisof all of the steroids of the body.
23.4C SEX HORMONES
The sex hormones can be classified into three major groups:(1) The female sex hormones, or setrogens.(2) The male sex hormones, or androgens.(3) The pregnancy hormones, or progestins.
H3C
H
H
H
HO
OHH3C
H
H
H
HO
O
Estrone(´Æ¼¤ËØͪ )
Estradiol (´Æ¶þ´¼)
The first sex hormone to be isolated was an estrogen, estrone.
The examples of the second sex hormones:
H3C
H
H
H
O
OH3C
H
H
H
HO
OH
Anfrosterone (ÐÛçÞͪ )
Testosterone (غÍè ¼¤ËØ)
H
CH3 H3C
Testosterone and estradiol are the chemical compounds from which “maleness” and “femaleness” are derived. The differ of their structure is slightly.
Progesterone and norethindrone are the most important progestin.
H3C
H
H
H
O
COCH3
H3C
Progesterone (»ÆÌå ͪ )
23.4D ADRENOCORTICAL HORMONES
H3C
H
H
H
O
OH
H3C
Norethindrone (Ȳŵͪ )
C CH
At least 28 different hormones have isolated from the adrenal cortex.Included in this group are the following two steroids:
H3C
H
H
H
O
COCH2OH
H3C
Cortisone (¿ÉµÄËÉ)
OH H3C
H
H
H
O
COCH2OH
H3C
OHHO
Cortisol(Ç⻯¿ÉµÄËÉ£©
O
Most of adrenocortical steroids have an oxygen at position 11. cortisol is the major hormone synthesized by the human adrenal cortex.
23.4E D VITAMINS
The following reaction can produce vitamin D2. The photochemical reaction that takes place is one in which the dienoid ring B ofergosterol opens to produce a conjugated triene.
H3C
H
HO
H3C
H3C
H
HO
CH2UV light,room tempreature
Vitamin D2 (άÉúËØD2£©
23.4F OTHER STRUCTURE
Digitoxigenin is a cardiac aglycone that can be isolated by hydrolysis of digitalis.
Cholic acid is the most abundant acid obtained from the hydrolysis of human or oxbile.
H3C
H
H
H
HO
H3C
OH
H
H
HO
CH
H
CH3 H3C
H
OO
Digitoxigenin(ÑóµØ»Æ¶¾ÜÕÅä»ù)
HOH
HO
CH2CH2COOHH3C
Cholic acid (µ¨Ö Ëᣩ
Stigmasterol is a widely occurring plant steroid that is obeainedcommercially from soybean oil
Diosgenin is obtained from a Mexican vine, cabeza de negro,Genus Dioscorea. It is used as the starting material for a commercial synthesis of cortisone and sex hormones.
H3C
H
H
H
HO
H3C
OH
H
H
HO
CH3
H3C
O
O
CH3
H3C
Stigmasterol diosgenin(ÊíÝ÷ÔíÜÕÅä»ù)
23.4G REACTIONS OF STEROIDS
The stereochemistry of steroid reactions is often quite complex. It is strongly influenced by the steric hindrance presented at the β faceof the molecular methyl groups. But many reagent react preferentiallyrelatively at the α face (the formula on next page).
HO
CH3 H
H
O
5 ,6 -Epoxycholestan-3 -ol (only product)
HCl
HO
CH3 H
H
O
H
+
+ Cl-
6HO
CH3 H
H
OH
5
Cl
When the epoxide ring of 5 α ,6 α -Epoxycholestan-3 β -ol is opened,Attack by chloride ion must occur from the β face, but it takes place at the more open 6 position.
H3C
H
H
HHO
CH3
H2, Pt
C6H5COOOH
(1) THF: BH3(2) H2O2, OH-
HO
CH3 H
H
H3
4
5
6HO
CH3 H
H
O
5
HO
CH3 H
H
HOH
5 -Cholestan-3 -ol (85-95%)
5 ,6 -Epoxycholestan-3 -ol (only product)
5 -Cholestane-3 ,6 -diol (78%)
Cholesterol (µ¨ ¹Ì ´¼)
The relative openness of equatorial groups also influences the stereochemical course of steroid reactions.
HO
H H
CH3
OH
H3
4
56
C2H5OOCO
H H
CH3
OH
HC2H5OCOCl
(excess)
23.5 PROSTAGLANDINS
Prostagkandins are C20-carboxylic acids that contain a five-membered ring, at least one double bond, and several oxygen-Containing functional groups. Two of the active prostaglandinsare prostaglandin E2 and prostaglandin F1α.
56CO2H
CH3
O
HO HOH
H
9
11 15
1
20 CH3
HO
HO HOH
HCO2H
Prostaglandin E2 (Ç°ÁÐÏÙËØ E2)
Prostaglandin F1 (Ç°ÁÐÏÙËØ E2)
The biosynthesis of prostaglandins of the 2 series begins with aC20 polyenoic acid, arachidonic acid.
CO2H
CH3
Arachidonic acid (»¨ ÉúËÄÏ©Ëá)
2O2cyclooxygenase
CO2H
CH3
O
OH
O2H
H
(»· ×´ÄÚ¹ý Ñõ»¯Îï £©
PGC2
several steps PGE2 and other prostalandins
23.6 PHOSPHOLIPIDS AND CELL MEMBRANES
Most phospholipids acid are structurally derived from a glycerolderivative known as a phosphatidic acid.
CH2OCOR
CHOCOR'
CH2 O P OH
OH
O
From fatty acid
From phosphoric acid
23.6A PHOSPHATIDES
In a phosphatidic acid, two hydroxyl groups of glycerol are joined
in ester linkages to fatty acids and one terminal hyfroxyl group is
joined in an ester linkage to phosphoric acid.
In phosphatides, the phosphate group of a phosphatidic acid is boundthrough another phosphate ester linkage to one of the following nitrogen-containing compounds.
HOCH2CH2N+(CH3)3 HO- HOCH2CH2NH2
HOCH2
NH3+
H
CO2-
Choline (µ¨¼ï)
2-Aminoethanol (2-°±»ùÒÒ́¼)
L-Serine(L-Ë¿°±Ëá)
The most important phosphatides are the lecithins, cephalins, phosphatidyl serines, and plasmalogens.
H2C
HC
H2C
O C R
O C R'
O P OCH2CH2N+(CH3)3
O
O
O
O-
Lecithins (ÂÑÁ×Ö¬)
H2C
HC
H2C
O C R
O C R'
O P OCH2CH2NH3+
O
O
O
O-
Cephalins (ÄÔÁ×Ö¬)
H2C
HC
H2C
O C R
O C R'
O P OCH2CHNH3+
O
O
O
O-CO2
-
H2C
HC
H2C
OR
O C R'
O P OCH2CH2NH3+
O
O
O-
Plasmalogen (ËõÈ©Á×Ö¬)
phosphatidyl serines (Á×Ö¬õ£Ë¿°±Ëá)
Like soaps and detergents phosphatides “dissolve” in aqueous mediaby forming micelles.
The hydrophilic and hydrophobic portion of phosphaides form a portion of a structure unit that creates an interface between an organic and an aqueous environment.
23.6B DERIVATIVES OF SPJINGODINE
Another important group of lipids is derived from sphingosine.
On hydrolysis, sphingomyelins yield sphingosine, choline, phosphoric acid, and a C24 fatty acid called lignoceric acid.
H3C(H2C)12 H
CHOHH
CHNH2
CH2OH
H3C(H2C)12 H
CHOHH
CHNHCO(CH2)22CH3
CH2OPOCH2CH2N+(CH3)3
O
O
Sphingosine (ÇÊ°±´¼)
Sphingomyelin (ÇÊÁ×Ö¬)
23.7 WAXES
Most waxes are esters of long-chain fatty acids and long-chainalcohols. Waxes are found as protective coatings on the skin,fur, or feathers of animals, and on the leaves and fruits of plants.