Organic Lecture Series

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Organic Lecture Series •• 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

2 Organic Lecture Series • Lipids include –triglycerides, phospholipids, prostaglandins, prostacyclins, and fat-soluble vitamins –cholesterol, hormones, and bile acids

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Organic Lecture Series TriglyceridesTriglycerides •• Triglyceride:Triglyceride: an ester of glycerol with three fatty acids

O CH OCR O 2 CH 2 OH RCOOH 1. NaOH, H2 O R' COCH O HOCH + R'COOH 2 . HCl, H O 2 CH OH R' ' COOH CH 2 OCR'' 2 A triglyceride 1,2,3-Propanetriol Fatty acids (Glycerol, glycerin)

4 FattyFatty acidacid Organic Lecture Series • Fatty acid: a 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 (16:0), stearic acid (18:0), and oleic acid (18:1)

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FattyFatty acidacid Organic Lecture Series

–the three most abundant are palmitic (16:0), stearic acid (18:0), and oleic acid (18:1) –In this labeling system: (carbon #:alkene #)

palmitate (16:0) oleate (18:1) O O CH 2 OC(CH2 ) 14CH3 stearate (18:0) CH3 (CH2 )7 CH= CH( CH2 )7 COCH O CH 2 OC(CH2 ) 16CH3

6 FattyFatty acidacid Organic Lecture Series –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

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Organic Lecture Series TriglyceridesTriglycerides

• 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

8 Organic Lecture Series TriglyceridesTriglycerides –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

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Organic Lecture Series TriglyceridesTriglycerides – example: a triglyceride derived from one molecule each of palmitic acid, oleic acid, and stearic acid, the three most abundant fatty acids in the biological world

palmitate (16:0) oleate (18:1) O O CH 2 OC(CH2 ) 14CH3 stearate (18:0) CH3 (CH2 )7 CH= CH( CH2 )7 COCH O CH 2 OC(CH2 ) 16CH3

10 Soaps and Detergents Organic Lecture Series • Natural soaps are prepared by boiling lard or other animal fat with NaOH, in a reaction called saponification (Latin, sapo, soap)

O CH OCR O 2 saponification RCOCH + 3NaOH O CH2 OCR CH2 OH O - + A triglyceride CHOH + 3RCO Na (a triester of glycerol) Sodium soaps CH2 OH 1,2,3-Propanetriol (Glycerol; Glycerin)

COO-Na+

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Organic Lecture Series 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

12 Organic Lecture Series – a soap micelle: nonpolar (hydrophobic) hydrocarbon chains cluster in the inside and polar (hydrophilic) carboxylate groups lie on the surface

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Organic Lecture Series 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

14 Organic Lecture Series Prostaglandins • Prostaglandins: a family of compounds that have the 20-carbon skeleton of prostanoic acid

5 3 1 9 7 8 6 4 2 COOH 10

11 12 14 16 18 20 13 15 17 19 Prostanoic acid

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Prostaglandins Organic Lecture Series • 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 (notice the all cis configurations)

9 8 6 5 COOH

11 12 14 15 Arachidonic acid 16 9 8 6 5 Organic Lecture Series COOH

11 12 14 15 Arachidonic acid

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Organic Lecture Series Prostaglandins • Research on the involvement of PGs in reproductive physiology has produced several clinically useful derivatives

–(15S)-15-methyl-PGF2α is used as a therapeutic abortifacient extra methyl group HO at carbon-15 9 COOH

15 11 HO HO CH3

(15S)-15-Methyl-PGF2α 18 Organic Lecture Series Prostaglandins the PGE1 analog, misoprostol, is used to prevent the ulceration associated with the use of aspirin-

like NSAIDs* O COOH

PGE1 16 15 HO HO H

O COOCH Misoprostol 3 HO CH3

16 HO 15

*Non-Steroidal Anti-Inflamatory Drugs 19

Organic Lecture Series • Steroids: a group of plant and animal lipids that have this tetracyclic ring structure:

CD

AB

• The features common to the ring system of most naturally occurring steroids are:

20 Steroids Organic Lecture Series

– 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-trans CH3 CH3 H

H H H 21

Organic Lecture Series Cholesterol is the Precursor for Families of Steroids

bile acids (e.g., cholic acid)

sex hormones (e.g., and estrone) cholesterol mineralocorticoid hormones (e.g., aldosterone)

glucocorticoid hormones (e.g., cortisone)

22 Organic Lecture Series Synthetic Anabolic Steroids – a way to increase the testosterone concentration is to use a “prohormone”, which the body converts to testosterone; for example “andro” HO OH H C H3 C 3 CH3 H3 C CH3 H H3 C H HH HH O O H Methandrostenolone Methenolone O

OC(CH2 )8 CH3 H C O H3 C 3

H CH 3 H3 C H

HH H H O O decanoate 4-Androstene-3,17-dione (andro) 23

Organic Lecture Series Synthetic Estrogens

• Progesterone-like analogs are used in oral contraceptives HO H C CCH "Nor" refers to the absence 3 of a methyl group here. H H The methyl group is present in ethindrone H H

CH3 O H C C= O Norethindrone 3 H

H3 C H

H H O Progesterone 24 Organic Lecture Series Cholesterol

H3 C H C 3 H

H H HO

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Biosynthesis of Steroids Organic Lecture Series

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 Stage 2: synthesis of cholesterol Stage 3: conversion of cholesterol to other steroids

bile acids (e.g., cholic acid) sex hormones (e.g., testosterone and estrone) cholesterol mineralocorticoid hormones (e.g., aldosterone)

glucocorticoid hormones (e.g., cortisone) 26 Organic Lecture Series Biosynthesis of Cholesterol O HO CH O 3 - CH3 -C-S-CoA O OH Acetyl Coenzyme A (R)-Mevalonate

3- OP2 O6 Isopentenyl pyrophosphate Details C10terpenes (C10) Geranyl pyrophosphate

C15and C20 terpenes (C15) Farnesyl pyrophosphate

C30terpenes (C30) Squalene

Cholesterol 27

Organic Lecture Series

Isopentenyl Dimethylallyl pyrophosphate pyrophosphate

Geranyl pyrophosphate

Details

28 Organic Lecture Series

Squalene Oxide

O

4-ring closures Form the ABCD ring system HO 29

Organic Lecture Series H H Loss of proton; 2 hydride and 2 methyl group shifts gives H CH3 Lanosterol CH3 HO H

CH3

CH3 Lanosterol HO 30 Organic Lecture Series H

CH3

SEVERAL CH3 Lanosterol STEPS HO

H3 C H C 3 H

H H HO cholesterol 31

Organic Lecture Series

O HO CH O 3 - CH3 -C-S-CoA O OH Details Acetyl Coenzyme A (R)-Mevalonate

3- OP2 O6 Isopentenyl pyrophosphate

C10terpenes (C10) Geranyl pyrophosphate

C15and C20 terpenes (C15) Farnesyl pyrophosphate

C30terpenes (C30) Squalene Lanosterol

Cholesterol 32 Organic Lecture Series O Equivalent to a O O Claisen condensation SCoA SCoA O Acetoacetyl CoA

SCoA Acetyl CoA O O H 3 C OH

O SCoA

β -h ydroxy-β -m ethylg lutaryl CoA HMG-CoA 33

Organic Lecture Series O H C OH O 3 β -hydroxy-β -m ethylglutaryl CoA HMG-CoA O SCoA

NADPH + 2H+ HMG-CoA reductase

CoASH + 2NADP+ This is inhibited by the "statin" drugs

O OH H 3 C OH

Mevalonate O 34 Organic Lecture Series

Atorvastatin Lipitor

Simvastatin Zocor Lovastatin Mevacor

Pravastatin Pravacol 35