LIPIDS

They constitute he most abundant fraction of lipids and are present both in plants and in animals as energy storage.

Fats, oils, waxes

Esters of fatty acid

“fatty acids" are carboxylic acids of long unbranched chain, with evennumber of C atoms, saturated or unsaturated, with a number of C atomsusually from 12 to 20.

A lipid is defined as a naturally occurring organic compound that is insoluble inwater, but soluble in nonpolar organic solvents. Therefore, they include many typesof compounds.

Lipids: structurally different compounds, related to each other by a shared physical property, that is solubility in nonpolar or scarcely polar solvents (Hydrocarbons, chloroform, diethyl ether)

Fats and oils are triglycerides or triacylglycerols, both terms meaning “triesters of glycerol (1,2,3-propanetriol).

Waxes: simple ester of fatty acids with long chained alcohols.

CH3(CH2)14CO2(CH2)29CH3O

O

Example:

triacontyl hexadecanoate (bee wax)

CH2CHCH2

OHOHOH

CH2CHCH2

OO

ORO

R'O

R"O

glycerol1,2,3-propanetriol

R, R', R" may be equal or different, saturated or unsaturated

R CO

from 12 to 20 C

Saturated fatty acids are solid at room temperature (grease), because zig-zaghydrocarbon chains can fit compactly together, resulting in high van derWaals attractions.

Searic acid (octadecanoic acid)

CH2CH3CH2CH2 CCH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2 OH

O

Example:

O

OH

linolenic acid (9,12,15-ottadecatrienoic acid)

CH H

CH2CH3C C

CH2C

H H

CH2C

CH2 CCH2CH2CH2CH2CH2CH2

C

OH

OH H

191215

The presence of cis double bonds prevents the formation of neat, compactlattices and chains tend to coil and liquid at room temperature (oil)

Example:

O

OH912

15

CH2CHCH2

OHOHOH

CH2CHCH2

OO

OC

C

CRO R'

O

R"O

O C R"O

-

CROO-

C R'O

O-

glycerol

NaOH

Na+

+Na+

Na+H2O

Basic hydrolysis give glycerol and carboxylates of fatty acids (soaps)

In an organism, ingested fats are hydrolyzed into mono- and diglycerids, fatty acids, and glycerol, all absorbed hrough the intesinal wall.

CH2 OCORCH OCORCH2OCOR

CH2 OHCH OCORCH2OCOR

CH2 OHCH OHCH2 OCOR

CH2 OHCH OHCH2OH

H2Oenzymes + + + RCO2H

diglyceride monoglyceride glycerol fatty acid

Soaps are characterized by a polar head (carboxylate anion) and long nonpolar chains.

CO2-

Soaps in water do not dissolve, but aggregate giving micelles, clusters of hydrocarbonchains with their ionic heads facing the water. They do not dissolve, but the solutionlooks homogeneous.

grease

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2OH2O

H2O

H2OH2O

The soap micelles emulsify oily dirt, including it in the nonpolar core of micelle.

Detergents (synthetic solfonates) work in the same way

SO3- Na

+

Phospholipids

Phospholipids are lipids that contain phpsphate ester groups. They are of different types.Phosphoglycerids: they are closely related to the fats and oils. Thesecompounds usually contain fatty-acid esters at two positions ofglycerol with a phpsphate ester a the third position

R' contains a positive charge

such as, for exsmple:

CH2CH2 N(CH3)3O+

choline

They can be found almost exclusively in cell membranes

OO CO

CH2 N(CH3)3

CH2

CH

CH2O

O PO O

O CH2C

-+

polar head nonpolar tails

CH2CHCH2

OO

ORO

RO

PO

OHO R'

phosphatidylcholine (a lecitin)

Fosfatidiletanolammina (una cefalina)

C R

CH2 N(CH3)3O P O

OO

CH2

CH2

COCO

O

OCH2

HR+

-L

C R

CH2 NH3O P O

OO

CH2

CH2

COCO

O

OCH2

HR+

-

Lecithins and cephalins are two types of phpsphoglyceride hat are found in the brain, nerve cells, and liver of animals and are aldo found in food (egg yolks, wheat germ, yeast, soybeans, etc.)

phosphatidylethanolamine (a cholin)

CHCH2

OHN

OR'

HH

R"R',R" = HR' = COR, R" = H

R'= COR, R"= glycoside glycosphingolipidsceramidessphingosine

CHCH2

OHN

O PO

OO

H

OR"

N(CH3)3+

-sphingomyelin

Component of membranes and of myelinic coating of nervous cells

Sphingolipids

Example:

Sphyngomyekin is a phosphate ester of a long-chain allyl alcohol with an amide side chain.

Terpenes

All terpenes contain a number of C atoms multiple of 5. Sequences of 4 Cs + 1C in the side chain are repeated

The 5 carbon atoms structure is said “isoprene unit”: the end closer o the methyl branch is called “head”, the other end is indicated as “tail”.

headtail

The name “isoprene unit” derives from isoprene (methylbutadiene); acually, the unit involved in the biogenetic process is isopentenyl pyrophosphate

OO PO

OOP

O

O isoprenemethylbutadiene

-- -

isopentenyl pyrophosphateSimplest terpenes contain two isoprene units.

The odorous components of plants that can be separated from other plant materials by steam distillation are called essenial oils. Many essential oils are used in perfumes. Most essential oils are mixtures of terpenes, a class of natural products found in both plants and animals.

GLOSSARYó Terpenes with TWO isoprene units (C10) are monoterpenes.ó Terpenes with THREE isoprene units (C15) are sesquiterpenes.

ó Terpenes with SIX isoprene units (C30) are triterpenes.

ó Terpenes with FOUR isoprene units (C20) are diterpenes.

ó Terpenes with EIGHT isoprene units (C40) are tetraterpenes.

Generally, terpenes are constructed by the head-to-tail joining of isoprene units. However, head-to-head and tail-to-tail are also present.

tail

myrcenehead

tail

head a-pinene

limonene

(lemon)

10 C: two isoprene units monoterpene

zingiberene(ginger)

15 C: three isoprene units sesquiterpene

examples

myrcene(laurel)

10 C: two isoprene units monoterpene (head-to-tail)

a-pinene(conifers)

10 C: two isoprene units monoterpene

b-Carotene

tail-to-tail junction C 40: tetraterpene

H2OC H

OH

CO2HCO2H CH2

O H

OHCO2H CH2

OOH

Gibberelline A13

20 C: diterpene (considered a terpene, even if with only 18 C)growth hormone in plants

gibberellic acid

OH

squalene

biosynthesis

cholesterol

C 30: triterpene

biosynthesized by dimerization of two sesquiterpene (C 15) units

a steroid

C 40: tetraterpene

phytoene

SteroidsPolycycles with the structure of cyclopentanoperhydrophenanthrene

A B

C D1

2

34 5

67

8910

1112 13

14 15

16

17

Often methyl groups are present in 10 (number 19)and in 13 (number 18), called angular methylgroups; a C chain may be present in 17 (numbersfrom 20 on)

Tridimensional structure of steroids depends on the type of ring junction

Junctions between B and C rings and between C and D rings are ALWAYS transJunction between A and B rings may be either trans or cis

A B

bicyclo[4.4.0]decane (decalin)

Reference compound:

A and B rings are numbered first, then C ring and finally D ring are numbered, followed by side chains, if any

H

HHH

H

HH

H

H

H HH

H

H

HH

H

H

HHH

H

H

H

H

H

H

H HH

H

H

HH

H

H

2.5 Å

trans-decalineall chair boat-chair

H

H

H

H

H

H

H

H

HHH

H

HH

HH

H

H

2.17 Å

cis-decaline

Tridimensional structure of steroids:

CH3CH3 R

H

CH3CH3 R

H

5-a

b face

a face5-b

Steroids with trans A-B junction are called “5-a”, those with cis junction are indicated with “5-b”.

Systematic names of steroids are based on the saturated tetracyclic alkane with the same skeleton of C atoms

Nomenclature of steroids

C1-C27 CHOLESTANEC1-C24 CHOLANEC1-C21 PREGNANEC1-C19 ANDROSTANEC1-C18 ESTRANE

12

34 5 6

78910

1112

1314 15

1617

18

1920

2122

2324

2526

27

Deviations from thes base-skeletons is indicated with a prefix

Substituents and double bonds are indicated with respective prefixes and suffixes,together the number of thiddlee position they occupy and eventually the indication aor b (if they are below or above, respectively, the middle plane of the steroid).

Examples:

O

O

O

OH

Nandrolonesemisystematic:19-nortesterone (nor = missing)systematic: 17b-hydroxy-4-estren-3-one

progesteronC 21: 4-pregnen-3,20-dione

O Cholesterol5-cholesten-3b-ol

Cholesterol is the only steroidabundant in vertebrated, but has nohormonal activity

OH

CO2HCH3

CH3

H

OH

CO2H

lithocolic acid3a-hydroxy-5b-cholan-24-oic acid

OH ergosterol

sterol of yeast, gives Vitamin D2when irradiated

O

O

O

OHOH

cortisone

Hormone of adrenal cortex, used for treatment of arthritis

ProstaglandinsThey are carboxylic acids with 20 Cs and a ring. Together with tromboxanes and leucotrienes, thei costituite the group of eicosanoidd (from eicosanoic)acid

CO2H1

2

3

4

5

6

789

10

11 1213

14

15

16

17

1820

19

Prostaglandins are involved in stimulation or inhibition of smooth muscle;in regulatione of gastric secretion; in regulation of blood pressure; inregulation of muscle of respiration; intervene in inflammatory, nervous, andreproduttive processes.

Nomenclatura use semisysthematic names

Nomenclature delle prostaglandins

1. Three capital letters are used; the first two are PG (for prostaglandin), the third indicates how the cyclopentane ring is substituted.

Prostanoic acid

R'

C5H11HOO

O

O

PGG

R'

R"

O

O

PGH

O

R"OH

CH2CH2CH2CO2H

PGI

I tromboxanes are indicated with lettersTX leucotrienesi with letters LT O

R'

R"O

TXAOH

OHR'

R"TXB

OR'

R"

OR'

R"

OR'

R"

OR'

R"OH

OHR'

R"OH

OHR'

R"OPGA PGB PGC PGD PGE PGF

more important

2.C9 configuration is indicated with subscript a (below the plane or b (above the plane)

CO2H CO2H

O O

a chain 1

2

3

4

56

7R'= or135

6

7

4 2

w chain R"= 1314 15 16

17

18

19

20or 13

14 15 16

17 18

19

20

Side chain linked to C8 is called a chain; Side chain linked to C 12 is calledw chain; double bonds may be present in side chains: their number isindicated with a subscript

3.

OH

OH

OH

CO2HCO2H

OH

O

OHProstaglandin E1 Prostaglandin F2a

OH

CO2H

O H

H

H

H

O

Trombossano A2

CO2H

OH

O

OH

prostaciclina

CO2HH S

H OH

NH

OCO2H

NH2Leucotriene D4