CARBOHYDRATESAlso called sugars, they are the most abundant group of biomolecules. Theyhave important biological functions, associated with their formation, theirproperties (alone or in combination with other biomolecules) and theirdecomposition.

From K.P.C.Vollhardt, Organic Chemistry

sucrose

Sugar cane

Carbohydrates are formed by plants from CO2 during photosynthesis. They supply almost all C to living organisms.

Historically the name derives from the empirical formula Cm(H2O)n

Today the term saccharide is replacing the term sugar

polyhydroxyaldheydes and polyhydroxyketones

They are polyfunctional compounds

They are divided into simple sugars (monosaccharides) and complex sugars (disaccharides, oligosaccharides, polysaccharides), composed of the union of several monosaccharides

MONOSACCHARIDES they are not hydrolyzedDISACCHARIDES they are hydrolyzed to 2 units of monosaccharides

OLIGOSACCHARIDES they are hydrolyzed to 3 ÷ 10 units of monosaccharides

POLISACCHARIDES they are hydrolyzed to more than 10 units monosaccharides

NOMENCLATURE

The systematic nomenclature of monosaccharides requires the suffix -ose

monose

a monose with aldheyde function is called aldose a monose with ketone function is called ketose

The number of C atoms (usually 3 to 11) is indicated by a prefix before the suffix -ose

tri-, tetra-, penta-, hexa-, hepta-, etc.

aldohexose means: monose with 6 C atoms and aldehyde function

ketopentose means: monose with 5 C atoms and ketone function

Simplest aldose: 2,3-dihydroxypropanal (glyceric aldehyde) OHH

CH2

CHO

OHaldotriose

simplest ketose: 1,3-dihydroxypropanone (1,3-dihydroxyacetone) C O

CH2

CH2

OH

OH

ketotriose

Aldoses with C atoms from 4 to 6 have trivial names still used by IUPAC. Some ketoses have trivial names

Ketoses are often referred to with the suffix -ulose

hexulose means: ketose with 6 carbon atoms

The suffix -ulose can be preceded by the prefix indicating how many are the C atoms,which is the position of the carbonyl and which is the configuration of the C atoms, thatis indicated with the name of the corresponding aldose.

the most common ketoses are 2-ketoses, therefore the number 2 is often omitted

Fischer notation is used to write monoses

OHHCH2OH

OHHOHHOHH

CHO

CH2OHOHH

CHO

OHHHOH

CHO

CH2OH

OHHOHH

CHO

CH2OH

CH2OHOHHOHHOHH

CHO

CH2OHOHHOHHHOH

CHO

CH2OHOHHHOHOH

CHO

CH2OHOHHHOHHO

CHO

OHHCH2OH

OHHOHHHOH

CHO

OHHCH2OH

OHHOH HH OHCHO

OHHCH2OH

OHHOH HOH H

CHO

OHHCH2OH

OH HOH HOH H

CHO

OHHCH2OH

OH HOHHOHH

CHO

O115HCH2OH

OH HOHH

OH HCHO

OHHCH2OH

OH HOH H

OHHCHO

D-glyceraldehydealdotriose

D-erythrose D-threose

aldotetroses

aldopentoses

D-ribose D-arabinose D-xylose D-lyxose

D-allose D-altrose D-glucose D-mannose D-gulose D-idose D-galactose D-talosealdohexoses

ALDOSES

Mnemonic rule: all altruist gladly make gum in gallon tanks

OHHCH2OH

OHHOHHO

CH2OH

CH2OHO

CH2OH

OHO

CHO

CH2OH

CH2OHOHHOHHO

CH2OH

CH2OHOHHHOHO

CH2OH

OHHCH2OH

OHHOH H

OCH2OH

OHHCH2OH

OH HOHHO

CH2OH

OHHCH2OH

OH HOH H

OCH2OH

dihydroxyacetoneketotriose

D-erythrulose

ketotetrose

ketopentoses

D-ribulose D-xylulose

D-psycose D-fructose D-sorbose D-tagatose

ketohexoses

KETOSES

L-monoses are MIRROR IMAGES of the corresponding D-monoses

OHHCH2OH

OHHOH HH OHCHO

OH HCH2OH

OH HOHHHOH

CHO

D-glucose L-glucose

CH2OHOHHHOHOHH

CHO

CH2OHOH HH OHOH H

CHO

D-xylose L-xylose

Some natural sugars do not have the carbonyl group and are called alditols They are named replacing the suffix -ose with the suffix -itol.

ALDITOLS

OHHCH2OH

H OHHOHOH

CH2OHH

It is present in apples, plums and red berries and finds industrial application as sweetener

NOTICE: Although there is not a more oxidized ending, this alditol is still considered as D-, because it maintains the structure of D-glucoseD-glucitol (D-sorbitol)

NOTICE: if the missing group is replaced by H, the substractive prefix is sufficient. Otherwise, the replacing group must be named

example:

CH2OHOHHOHHHH

CHO

CH2OHOHHOHHOHH

CHO

D-ribose

reference compound

2-desoxy-D-ribose

When an hydroxyl group is missing the SUBTRACTIVE NOMENCLATURE is used. The prefix de(s) indicates that the named group is missing from the reference compound.

OHHCH2OH

OHHOH HH NH2

CHO

D-glucosamineOHH

CH2OH

OHHOH HH OHCHO

D-glucose

2-amino-2-desoxy-D-glucose

ATTENTION! The name 2-amino-D-glucose means that the amino group replaces H (as usual) at position 2 of glucose

OHHCH2OH

OHHOH HNH2 OHCHO

Present in many aminoglycosidic antibiotics

reference compound

CYCLIC FORMS OF MONOSESFormulae considered insofar do not explain all the properties of monoses.

D-glucose exists in two different crystalline form named, a and b that, dissolvedin water, show different optical rotations, when immediately measured. However,with time the values change, converging toward the same value (mutarotation).

a-D-glucose mixture at equilibrium b-D-glucose[a]D +112∞ +52.7∞ +19∞

The carbonyl group of aldoses and ketoses reacts with an alcoholic–OH, giving a stable cyclic hemiacetal .

O

O

COH

CHOHCHOHCHOHCHOHCH2OH

5-membered cyclic hemiacetal FURANOSE

PYRANOSE

furane

pyrane

6-membered cyclic hemiacetal....

Which OH?

Generally, furanosidic rings form rapidly (kinetic control), whereas pyranosidic ringsare more stable and are predominant at the equilibrium (thermodinamic control)

Why D-glucose crystallizes in two form?

C ONu: the formation of cyclic hemiacetal generates anew chiral C, called anomeric carbon

Upon cyclization, TWO diastereomers originate

Diastereomers differing only for the configuration of anomeric C are called

anomers

Mutarotation is the consequence of the rapidly estabilished equilibrium in solution of the two cyclic anomers with the open molecule

a-D-glucoseKa

b-D-glucoseKb

OHHCH2OH

OHHOH HH OHCHO

Different notations can be used to represent the cyclic anomers.

1. Fischer formulaeThe Fisher projection of the open chain is maintained. Also the new chiral C has bonds projected in the form of a cross; O maintains the same position as OH relative to the carbon chain. Bonds appear deformed

COH

CH2OHOH

COH H

CH2OH

OC OHH

CH2OH

O

1

23

45

1 1

Da anomer b anomer

The anomer with the O bridge and the anomeric –OH are on the same side ofthe C atoms chan is called a; b is the anomer where they lay on opposite sides.

COH

OHCH2OH

C OHH

CH2OH

O

COH H

CH2OH

O

1

23

4

5

1 1

Da anomer b anomer6

5 5

Furanosidic form

Pyranosidic form

Analogous is the representation for ketoses:

CH2OH

C O

OHCH2OH

CH2COH

CH2OH

OHO

CH2 C OH

CH2

OH

OOH

CH2COH

CH2

OH

OOH

CH2 C OHOHO

CH2OH

1

23

45

6....

a anomer

D

a anomer

b anomer

b anomer

C 6 is not chiral, but the oxygen bridge is conventionally located on the right of the chain

COH

CH2OHOH

C OHH

CH2OH

OCOH H

CH2OH

O

1

2345

1 1

a anomerL b anomer

Naming a and b anomers follows the same rules: the anomer is called a when anomeric OH and oxygen bridge lay on the same side with respect to the C atoms chain (b when anomeric OH and oxygen bridge lay on opposite sides with rispect the chain).

If the OH acting as the nucleophile is on the left of the C atoms chain in the Fischer projection of the open form, the oxygen bridge must be written on the left side.

2. Haworth formulaeTo write a cyclic monose according to Haworth projections, the rules are as in the following.

a. The ring is represented as a pentagon or a hexagon, drawing them as planar andviewd in perspective. The other bonds are drawn above and below the plane, asvertical segments.

b. The furanosidic ring is oriented so that O occupies the upper vertex with theanomeric C (C1 for aldoses and C2 for ketoses) on the right of it.

c. The pyanosidic ring is oriented so that O occupies the upper right vertex, withthe anomeric C on its right

O

Ofuranosidic anomeric C C1 in aldoses

C2 in ketoses

pyranosidic anomeric C C1 in aldosesC2 in ketoses

Better representation of cyclic structure

Guidelines to convert Fischer formulas into Haworth formulas

For example: a anomer C OHH

CH2OHH

O

C OHH

CH2 H

O

OH

234

1

D6

5

234

1

65

Ø Write the Fischer formula so that all bonds out of the ring lay horizontally, on the left and on the right of the C chain.

ATTENTION! In doing so, be careful to move -CH2OH in the horizontal bond without changing the configuration of the chiral C

Ø All the bonds that in Fisher formula lay horizontally on the left of the C chain must be wtitten above the ring plane in the Haworth notation (and all the bonds on the right must be written below).

C OHH

CH2 H

O

OH

OCH2OH

H

OH

H234

1

65 23

4

5

6

1

NOTICE: following the procedure correctly, the terminal –CH2OH is up in the D series, down in the L series.

OCH2OH

HO

CH2OH

H

D LIn a anomer: CH2OH and OH are always opposite O

CH2OH

H

OH

H OCH2OH

HOH

D, a L, a

Example:CC OHOHH

OH HH OHCH2OH

H

OH

Write the anomers of the aldohexose on the right

Unless otherwise indicated, both pyranosidic AND furanosidic forms must be written

CC OHOHH

OH HH OHCH2OH

H

OH1

23

45

6

....

DH

C OHH

CH2OH

OHHOHH

H

O

OHH

COH H

CH2OH

OHOH

H

O

O

23

4

1

6

5

+ 23

4

1

6

5

ab

HOH

C OHH

CH2OH

OHHOHH

H

OHOH

COH H

CH2OH

OHHOHH

H

O23

4

1

6

5

+

23

4

1

6

5

ba

CHOH

C OHH

CH2OH

OHHOHHO

H CHOH

COH H

CH2OH

OHHOHHO

H

23

4

1

6

5

23

4

1

6

5HOH

C OHH

CH2

OHHOHH

H

O

OHHOH

COH H

CH2

OHHOHH

H

O

OH

234

1

6

5

234

1

65

OH

CH OH

H

OH

HOH

H

CH2

OHOH

OH

CH OH

H

OH

HOH

H

CH2

OHOHb a

OCH2OH

HOH

HOH

H

OH

HOH

H OCH2OH

HOH

HOH

H

OH

H

OH

H23

4

5

6

1

ba

3. Conformational formulas

Piranosidic forms are six-membered rings: the representation closest to the real molecule uses the chair conformations.

OO

Guidelines to pass from Haworth formulas to conformational formulas.ü Groups up in Haworth formula must be written as either axial or equatorial bond, depending on which is above the average ring plane in the chair conformation.

example:

OCH2OH

HOH

HOH

H

OH

HOH

H

H

HCH2OHH

OH

OH OHHH

OHO

OH

OHH

OH

HHH

OH

OH

CH2OH

23

145

6

1

234

5

6

123

45

6

Each pyranose exist in two chair conformations that interconvert: equilibrium is shifted toward the chair with less 1,3-diaxial interactions. Especially important is the -CH2OH, position, beause it is the bulkiest group. Moreover, it is linked to C5 (C-O bond shorter than C-C bond).

OO 1

41

44C1 1C4

1,3-interactions 1,3-interaction

1,3-interaction 1,3-interactions

The two anomers are indicated with 4C1 and 1C4, where C stays for chair , the superscript left number indicates the C above the ring medium plane, the subscript right number indicates the C below the ring medium plane.

OH

OHO

OHOH

CH2OHOH

OH

OHO

OHOH

CH2OH

OHCHOH

OOH CH

OH

CH2

a-D-glucopiranose b-D-glucopiranose b-D-galattopiranose

CH2OH

OH OHOHOH

O

CH2OH

OH

OHOHOH

O

a-D-idopiranose a-D-altropiranose

D-hexapyranoses generally prefer 4C1 conformation.

Examples of preferred 1C4 conformation:

CH2OH

OH

OHOH

OOH a-L-glucopiranose

Back to D-glucose mutarotation, now it is possible to understand the equilibrium composition: the b anomer has all the groups other than H in equatorial positions.

OH

OHO

OHOH

CH2OH

OHHCH2OH

OHHOH HH OHCHO

CH2OH

OHOHO

OHOH

a-D-glucopiranose b-D-glucopiranose

37.3% 0.002% 62.6%

BUT... substituents with electronegative atom linked at the anomeric C prefer the axial position

O

OHO

OHOH

CH2

R

OH CH2

OH

OOHO

OHOH

RROH, H+

R = Me 66% 34%R = H 34% 64%

L-hexapyranoses, with opposite configuration at C5, generally prefer 1C4 conformation.

Anomeric Effect

Anomers with equatorial ORare destabilized by repulsionof electron pairs (or ofaligned dipoles)

OO

RH

.... ..: O

O

RH

Anomers wih axial OR are stabilized byresonance (hyperconjugation)

Or by overlapping of the non-nondingp orbital of ring O with the antibondingle s* orbital of C1-O1 bond

O

O

RO R

O

1 -

+

OR

Oantibonding s* orbital of C1-O1 bond

O non bondingp orbital legante dell'O

with R=H the equatorial anomer predominates, because OH is more solvated than OR. Therefore OH, taking into account the solvation water molecukes, is bulkier than OR.

All the monoses that can form stable rings (5- and 6-membered) undergo mutarotation

Usually, 5-membered rings form faster, 6-membered rings are more stable and predominates at the equilibrium

example: equilibrium composition of an aqueous solution of D-glucose:

CC OH

OH HOHH

H OHCH2OH

H

OHCHO

HH

OH

H

OH

OH

H

CH2OHOH

OC

HH

OH

OH

HOH

OH H

CH2OHH

OC

HH

OH

OH

HOHOH

H

CH2OHH

CHO

HH

OH

H

OH

OH

H

CH2OH

OH OH

H

OHH

OH

OH

H

H

OH

CH2OHO

HH

OHH

OH

OH

H H

OHCH2OH

1

2

3

45

6

D

+

a-D-glucofuranose b-D-glucofuranose<1% <1%

+

a-D-glucopiranose b-D-glucopiranose36% 64%

REACTIONS OF MONOSES1. Reactions in basic medium

The reaction depends on the basicity of aqueous solution.It is advisable to avoid basic media with monoses.

In mild basic solution:

COH

H OH

R

COH

OH

R

H

COH

HOH

R

CO

H

OR

H

Haldose enol

aldose (of different configutation)

ketose

example: keto-enol tautomerism of glucose

OHHCH2OH

OHHOH HH OH

CHO

OHHCH2OH

OHHOH HOH H

CHO

OHHCH2OH

OHHOH H

OCH2OH

OHHCH2OH

OHHOH HH OH

CHO

D-glucose (57%)

NaOH ~10-2M

35°C, 100 h

D-mannose (3%) D-fructose (28%)D-glucosio

+ +

Monoses that differi inconfiguration of ONLY ONE CHIRAL CARBON are called

EPIMERS D-glucosie and D-mannose are a couple of 2-epimers (they differi only for the C2 configurazion)

in strongly basic media:The ketose (from keto-enol tautomerism) undergoes retro-aldol reaction, followed by aldol condensation, yielding 3- and 4-epimers.

OHHCH2OH

OHHOH HH OH

CHO

OHHCH2OH

OHOH H

OCH2OH

H

Ca(OH)2 1%

OHHCH2OH

COH

COH H

C OCH2OH

-+

C OHHCH2OH

COHH

COHH

C OCH2OH

miscela di prodotti

2. Reactions with alcohols (acetal formation)The monose hemiacetal reacts with alcohols in the presence of anhydrous acid catalyst, yielding acetal.

OCH2 OH

OHO

CH2 OOH

CH3CH3OH, H+

The –OR group is called aglycon

a-b interconversion is blocked. In principle, four different glycosides can be isolated.

OOH

OHO

OHCH2OH

CH3

OOH

OH

OOHCH2OH

CH3

O

OHO

OHOH

CH2OH

CH3

OOHO

OHOH

CH2OH

CH3

OH

OHO

OHOH

CH2OH

CHCH

OOH

OH

OHOHCH2OH

O

OHO

OHOH

CH2OH

HH

OOH

OH

OOH

CH2OH

H

H

OHO

OHOH

CH2OH

OOH

OHCH2OH

OH CH3 OH CH3

methyl a-D-glucofuranoside

methyl b-D-glucofuranoside

methyl a-D-glucopiranoside

methyl b-D-glucopiranoside

H+

+

+

- H2O- H2O

++

- H+ - H+

H+H+

- H+ - H+

POLYSACCHARIDESThey are acetals, originating by linking monose units.

A disaccharide is an acetal composed of two units of monosaccharide.This means that at least one of the units is linked through the hemiaceal OH.

Disaccarides are divided in two families:a) the acetal functionality is made with the hemiacetalic OH of one unit and

one alcoholic OH of the second unitglicosylmonose

DISACCHARIDES

glicosylglycoside

b) both units are linked using their hemiacetalic OH.

They are called reducing sugars (the free aldehyde functionality can be oxidized)

They are called non reducing sugars (no free aldehyde functionality present)

Example: 4-O-(b-D-ribofuranosy)-D-glucose One D-ribose unit, in b furanosidic form, is linked to the OH in 4 of D-glucose

OHH

C OHH

CH2OH

OHHHOH

H

OOHH

COH H

CH2OH

OHH

H

OH

C OHH

CH2OH

OHHHOH

H

O

C

OHH

H

CH2OH

OHH

H

OO

4-O-(b-D-ribofuranosyl)-D-glucoseD-glucoseb-D-ribose

- H2O

Glycosylmonoses are named as a derivative of the reductant monose.

Fischer formulas

Haworth formulas

OCH2OH

HH

OHH

OH

OH

H OHHOCH2

OH OH

OHOH OCH2

OH OH

OH OCH2OH

HH

H

OH

OH

H OHH

O

4-O-(b-D-ribofuranosyl)-D-glucose D-glucoseb-D-ribose

- H2O

OCH2

OH OH

OHOHOHOH

OOH OH

CH2

OH CH2

OH

OHOO

OH OHOCH2

OH OH

OH

4-O-(b-D-ribofuranosyl)-D-glucose D-glucoseb-D-ribose

- H2O

the conformation of disaccharide anomeric C remains undetermined, because it undergoes mutarotation (hemiacetal)

Glicosilglicosides are named indicating both units and glycosides and specifying the anomeric configuration.

a-D-ribofuranosyl-b-D-ribofuranosideTwo D-ribose units, in furanose ring, are linked through C 1 of both.

Configurazion of both anomeric C remains fixed (no mutarotation).

Conformational formulas

OHH

COH H

CH2OH

OHH

H

OOHH

CH OH

CH2OH

OHH

H

OOHH

CH O

CH2OH

OHH

H

OOHH

C H

CH2OH

OHH

H

O

b-D-ribosio

- H2O

a-D-ribofuranosyl-b-D-ribofuranosidea-D-ribose

Fischer formulas

OCH2

OH OH

OHOHOCH2

OH OHOH

OHOCH2

OH OH

OH OC

OH OH

OO

b-D-ribose

- H2O

a-D-ribosea-D-ribofuranosyl-b-D-ribofuranoside

or :

OCH2

OH OH

OHOH OCH2

OH OHOH

OH

OCH2

OH OH

OOH

OCH2

OH OH

OH

b a

each monose is the aglycon of the other.

Haworth formulas

SHORTENED NAMING

ó The monose is indicated with the first three letters of the name, except glucose, that is indicated as Glc (or G only) ó Generally, the pyranosidic form is not indicated; hoever, it is better to add p for pyranose, f for furanose. ó Substituents are indicated with additional letters

D-GlcN

examples:

2-amino-2-desoxy-D-glucose

D-GlcA6Et Ethyl D-glucuronate

a-D-Ribf-b-D-Ribf a-D-ribofuranosyl-b-D-ribofuranoside

From two identical hexapyranoses, 11 disaccharides are possible

Prefixes D-, L-, a-, b- precede abbreviations as necessary

DISACCHARIDES MORE PRESENT IN IN NATURE

Maltose4-O-(a-D-glucopyranosyl)-D-glucose

a-D-Glcp-(1 4)-D-Glc

CH2OH

OH

OO

OHOH

CH2OH

OOH

OHOH

From the hydrolysis of starch

CH2

OH

OH

OO

OHOH

CH2OHO

OHOH

OHCellobiose4-O-b-D-glucopyranosyl-D-glucopiranose

b-D-Glcp-(1 4)-D-Glc

From the hydrolysis of cellulose

OHO

OHOH

CH2OH

OH

OO

OHOH

CH2OHLactose4-O-b-D-galactopyranosyl-a-D-glucopiranoseb-D-Galp-(1 4)-D-Glcp

Only In mammals (up to 8.5% in human milk), is obtained commercially as a by-ptoduct in the manufacture of cheese.

OH

O

OH

OHCH2OH O

OHCH2

O OH

OH

OH

Trehalosea-D-glucopyranosyl-a-D-glucopyranosidea-D-Glcp(1 1)-a-D-Glcp

Energy storage in insects and mushrooms (15% of dry weight)present also as a,b and b,b isomers

O

O CH2OH

OH

OHO

OHOH

CH2

CH2 OHOH

OH

21

3

4

5 6

Not written according to Haworth notation

Sucrosea-D-glucopyranosyl-b-D-fructofuranosidea-D-Glcp-(1 2)-b-D-Fruf

Main energy source in plants, soluble in waterIt is used in food industry because, being not reducing sugar, does nor react with amino groups in proteins.

Acid (or enzimatic) hydrolysis produces gluccose and fructose Invert sugar

OH

OHO

OHOH

CH2OH

OCH2OH

HOH

H

H

OHCH2OH

OH

OHO

OHOH

CH2OH

OCH2OH

HOH

H

H

OHCH2OH

Oa

b+ H2O

O

O CH2OH

OH

OHO

OHOH

CH2

CH2OHOH

OH

OCH2OH

HOH

H

H

OHCH2OH

OH

OH

OHO

OH

OH

CH2OH

CH2OH

OH

OHO

OHOH

CH2OH

OHOHO

OHOH

a

b

H2O, H+

orinvertases

+

++

a-D-glucopyranose b-D-glucopyranose

c-D-fruttopyranoseb-D-fructofuranose

18% 32%

16% 34%

[a] + 66.5 + 52.7

- 92,4

- 39.7after hydrolysis

Opt

ical

rota

tion

chan

ges

from

pos

itive

to n

egat

ive

OLIGOSACCHARIDES

tri- and tetra- saccharides occur in nature at concentrations lower than that of disaccharides

OHO

OHOH

CH2

O

O

O CH2OH

OH

OHO

OHOH

CH2

CH2 OHOH

OHraffinose

a-D-Galp-(1 6)-a-D-Glcp-(1 2)-b-D-Fruf

Oligosaccharides can be described with a shortened nomenclature similar to that of monoses.

diffused in plants, by-product of sucrose from molasses of sugar-beet

non reducing sugar

OHO

OHOH

CH2

OCH2

HH

H

O

CH2OH

O

OHO

OHOH

CH2OH

OH

OH

OH

melezitosea-D-Glcp-(1 3)-b-D-Fruf-(2 1)-a-D-Glcp

In honey and in exudation of trees damaged by insects

non reducing sugar

Some cyclic oligosaccharides reached importance in organic chemistry

Cycloheptamaltose: caracterized by a non polar cavity and a polar external surface

O

OH

OHCH2

OH

OO

OH

OH

CH2OH O

O OH

OH

CH2O

O

OHOH

CH2OH

O O

OH

OHCH2OH

O

O

OH

OH

CH2OHO

OO

OHOH

CH2

OH

OH

with 6 units a-cyclodextrine

with 7 units b-cyclodextrinewith 8 units g-cyclodextrine

They can be obtained from starch with the enzyme ceclodetrina transglicolase

OCH3

OCH3

Cl

OCH3Cl

OCH3

Cl

OCH3HOCl

HOCl

b-ciclodextrin

+

96%only product

used in food, cosmetic and pharmaceutical industry

Cyclodextrins can complex small organic molecules, giving “inclusion compounds”, generally crystalline, even if the molecule is volatile. These inclusion compounds show a selectivity different from that of the free molecule.

CH2OHCH2OHCH2OHO

OOH OH

CH2O

OOH OH

OO

OH OHOO

OOH OH

OHetc.

etc.

poly-4-O-(b-D-Gp)Regular polysaccharides (i.e., those constituted by idntical monose units) are indicated adding the suffix -ANE to he name of monose

(1 4)-b-D-glucane

(1 4)-a-D-, (1 6)-a-D-glucane

(1 6)-b-D-glucane

cellulose linear

glycogen

dextrane(in bacterialsecretions)linear

branched

POLYSACCHARIDES

Polysaccharides most common in nature are homopolysaccharides, with a tridimensional structure thaat depends on how monoses are connected.

Ribbon polysaccharides

They are made of several thousands of monoses, with bonds linking monoses almost parallel

Polysaccharides can be described with a shortened nomenclature similar to that of monoses.

examples:

OO

OHOH

CH2

OOO

OHOH

CH2OH

OH

cellulose(1 4)-b-D-glucano

adjacenti glucosidic unities are rotated of 180°; insoluble in water

OOO

OOH

OH

OH OH

O

Glucane in oats is a 1®3, e,e polysaccharide, soluble in water

(1 4)-b-D-xylaneadjacenti xylosidic unities are rotated of 180°.

OO

O

OHCH2

OOO

OH

OHCH2CH3

OH

(1 4)-b-D-mannane

OH

CH2 OH

O CH3

O

CH2OH

OCH3

HH

OH

CH2 OH

O CH3

HH

O

OCH3

CHOHCH2OH

coniferyl alcohol

oxidativepolymerization

(radical reaction)

lignine(representative portion)

Cells of di ripe plants are made of microfibril of cellulose (50%) and xilane(20%) cemented by polymers of coniferyl alcohol (lignine)

Cellulose is the most abundant organic compound on earth. It forms the fibrous component of plant cell walls, together other more flexible ribbon-polysaccharides (xylane and mannane).

OO

OHNHAc

CH2OH

OOO

OHAcHN

CH2OH Chitin(1 4)-2-acetamido-2-desoxi-b-D-glucane

Main component of crustacea shell and insects exoskeleton, It forms rigid sheets, insoluble in water.

Bacterial cell walls contain more than 40% of a peptidoglycane similar to chitin

OO

ONHAc

CH2

OOO

ONHAc

CH2 CH3

HAlaO

OH

OH

Ala

Ala

po

ylsacc

arid

h

n

Peptide

Peptide

Peptide

n = 10-65

very strong network

4) b-D-GlcpNAc(1 4) 3-lactyl b-D-GlcpNAc(1

Polysaccharides "egg-box"

example: pectin

Inserted calcium ions confer the polymers the capability of strong cohesion. Therefore pectins are used as jelling agents in the making of preserves and jellies from fruit .

Ca++ Ca++ Ca++ Ca++ Ca++ Ca++

O

O

O

OH

OHO

OO

O

O

OO

O

H

H

O OO

OH

OHOO

O

O

O

OO

O

H

H

-

-

-

-

.

. ..

. ...

.....

..

..

..

....

..

..... ..

.......

...

...

... .. ......

.. .

..

..

..

...

.... .

....

..

...........

..

Ca++

1,4-Diaxial connections of monose units maintain the connecting bonds psrsllel, but shifted for the length of one monose unit, thus forming hollows bvetween pairs of adjacent monoses. Interactions among atoms of the couple are unfavourable, unless cavities are filled with water or ions

Polymers of galacturonic acid, pectina are found in fruit and in cell walls of several plants.

Helicoidal Polysaccharids

The two connecting bonds have the shape of a VThey tend to form a spiral if hydrogen bonds can exist along the helix axix. In absence of favourable interactions, they present random coils, with continuouslu fluctuating conformations.

usually, they are partially soluble in water.

O

O

O

OH

CH2

H

OH

OO

OHOH

O

O

O

OH

CH2

OOOH

OH

CH2

O

OH OH

CH2

O

O

OH

OHCH2OH

O

O

OHOH

CH2OH

OH

CH2OH OH

OH

hydrogen bond

... ..

gliycogen present in animalsstarch abundant in plants

Starch and glycogen are used as energy storage: hey must form concentrated deposits, but also to be readily available and released, when necessary.

(1 4)-a-D-glucaneStarch is composed of two fractions: amylose and amylopectin

Amylose: long linear chains (1000-2000 units); each coil contains from 4 to 8 glucose units, kept together by hydrogen bonds. The internal hollow tube is hydrophobic. with I2inside the coils, iodine atolms align, giving a dark violet complex

examples:

Amilopectin: 106 glucose units, with branches in position 6 every ca. 20 units. Therefore, extended helicoidal structures are impossible.

amylopectin

a-1,4’-glycosidic bond

a-1,6’-glycosidic bond

glycogen

Glycogen: similar to amylopectin, with branches every 11 units