Lecture 13

FATTY ACIDS and Steroids

Convener

Dr. Fawaz Aldabbagh

Lipids – water insoluble compoundsExcess carbohydrate (high energy foods) are stored as lipids, called fats.No definite structural grouping – include fats, oils, waxes, steroids + derivativesUses – Insulation, protection, help maintain correct body temperature, covering of nerve fibres + major structural material in cells

Two major groups – Saponifiable lipids and Non-Saponifiable lipids

Fatty Acids – naturally occurring long chain carboxylic acids

Unbranched carbon chain with an even number of carbon atoms

Long-chain fatty acids – 12-26 carbons are found in meat and fishMedium-chain fatty acids – 6-10 carbonsShort-chain fatty acids – less than 6 are found in dairy products

H

CH

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

O

OH

Hexadecanoic ac id (palmitic ac id)

COOH

H3C (CH2)14 C

O

OH

This is an example of a saturated fatty acid

COOH

Monounsatuarated

HH

Polyunsatuarated – have a carbon chain in which two or more DBs are present

COOH

linolenic acid

linoleic acid

COOH

These are Essential Fatty Acids

Fats and Oils are Esters

CH2

CH

CH2

OH

OH

OH

Glycerol

1,2,3-Propanetriol

Triacylglycerol (triglyceride)

CH2OC

CHO

CH2O

O

R

C R

O

C R

O

+ 3 NaOH

H2C

C

OH

OH

H2C OH

Glycerol

C

C

C

C R

OC R

O

O

R O Na

+

Sodium Carboxylate Soaps

H O

H

H O C

O

R

OH

H

H

H

H

H

H

H

H

H

H

axial

equatorial

cis-Decalin

equatorial

equatorial

trans-Decalin

H2C

H2CCH2

CH

H2C

CH2

CH2

CH2

H2CFused Bicyclic

Systems

cis is the same sidetrans opposite sides

H

H

axial

equatorial

axial

equatorial

Steroids can be isolated from the lipid fractions of animals and plants

Most show dramatic physiological effects when administered

A B

C DCH3

CH3

1

2

34

56

7

8

9

1112

1314

15

16

17

18

19

10

CH3

CH3

HOH

HH

H

H

Cholestanol

HO

all trans-junctions (equatorial-equatorial)

Cholestanolequatorial

CH3

H

CH3

H

H3C

CH3

CH3

HO Cholesterol

Isolated from nearly all animal tissuesGallstones are particularly rich in cholesterol Intermediate in the biosynthesis of other steroids

8 stereocenters28 = 256 possible isomeric forms

Sex Hormones1. The female sex hormones (estrogens)2. The male sex hormones (androgens)3. The pregnancy hormones (progrestins)

CH3

H

H H

O Progesterone

C O

CH3

CH3

CH3

H

H H

O Testosterone

OH

CH3

OHCH3

H

H H

HO

4 tonnes of sow overies gave 12 mg of estradiol

Estradiol

CH3

H H

HO

Ergosterol

CH3

CH3

H3C

H

CH3

H

HO

Vitamin D2

CH3

H3C

H

CH2

UV light

Sun-light helped to cure ricketsErgosterol was isolated from yeastAnd was found to be highly active