Download 22A - chemistry

Chapter 22
Carbohydrates
Carbohydrates

Fun Facts:


Photosynthesis converts more than
100 billion metric tons of CO2 and H20
into carbohydrates annually.
Non-photosynthetic cells can make
there own glucose from amino acids,
fats and other breakdown products.
Carbohydrates

Fun Facts 2

Mole Ratios 1C, 2H, 1O




Empirical Formula = CH2O
monosaccharides have from 3 to 8
carbons
aldose: linear sugar with an aldehyde
group
ketose: linear sugar with a ketone group
Carbohydrates

Fun Facts 3

Three classes of carbohydrates

Monosaccharides


Disaccharides


3 to 8 carbons with carbonyl and alcohol FG
2 monosaccharides connected with a ketal
or acetal connection
Polysaccharides

Multiple ketal or acetal connections
Monosaccharides

Monosaccharides are classified by
their number of carbon atoms
Name
Formula
Triose
Tetrose
Pentose
C3 H6 O3
C4 H8 O4
Hexose
Heptose
Octose
C5 H1 0 O 5
C6 H1 2 O 6
C7 H1 4 O 7
C8 H1 6 O 8
Monosaccharides

And they differ by the type of
carbonyl present


Aldehyde
Ketone
Monosaccharides

There are only two trioses
CHO
CH2 OH
CHOH
C= O
CH2 OH
Glyceraldehyde
(an aldotriose)

CH2 OH
D ihydroxyacetone
(a ketotriose)
often aldo- and keto- are omitted and these
compounds are referred to simply as trioses
Monosaccharides

Glyceraldehyde, the simplest aldose,
contains a stereocenter and exists as a
pair of enantiomers
CHO
CHO
H
C
OH
CH2 OH
HO
C
H
CH2 OH
Monosaccharides

Fischer projection: a two dimensional
representation for showing the configuration of
tetrahedral stereocenters


horizontal lines represent bonds projecting forward
vertical lines represent bonds projecting to the rear
CHO
H
C
OH
CH2 OH
con vert to
a Fischer
projection
CHO
H
OH
CH2 OH
D,L Monosaccharides

Emil Fischer decided on of D- and Lassignments for the enantiomers of
glyceraldehyde


D-monosaccharide: the -OH is on the right
L-monosaccharide: the -OH is on the left
CHO
H
OH
CHO
HO
H
CH2 OH
CH2 OH
D-Glyceraldehyde
L-Glyceraldehyde
[]25 = +13.5°
[]25 = -13.5°
D
D
D,L Monosaccharides

the most common D-tetroses and D-pentoses
CHO
H
OH
H
OH
CH2 OH
D -Erythros e
CHO
HO
H
H OH
CHO
H
OH
H
OH
H
OH
CH2 OH
D -Threose
CH2 OH
D-Rib os e
CHO
H
H
H
OH
H
OH
CH2 OH
2-Deoxy-D -rib os e
D,L Monosaccharides

the three common D-hexoses
H
HO
H
H
CHO
OH
H
OH
OH
CH2 OH
D-Gl u co s e
H
HO
HO
H
CHO
OH
H
H
OH
CH2 OH
D-Gal acto se
CH2 OH
C=O
HO
H
H OH
H OH
CH2 OH
D -Fru c tos e
Amino Sugars

Amino sugars contain an -NH2 group in place
of an -OH group
CHO
H NH2
HO H
H OH
H OH
CH2 OH
CHO
H2 N 2 H
HO H
H OH
H OH
CH2 OH
CHO
H NH2
HO H
HO 4 H
H OH
CH2 OH
H
HO
H
H
CHO O
NHCCH3
H
OH
OH
CH2 OH
D -Glucosamine D -Man nosamine D -Galactosamine N-Acetyl-D (C-2 stereoisomer (C-4 stereois omer glu cosamine
of D -glu cosamine of D -glucos amin e)
Cyclic Structure

Aldehydes and ketones react with alcohols to
form hemiacetals

cyclic hemiacetals form readily as five- or sixmembered ring
O
4
1
H
red raw to show
-OH an d -CHO
clos e to each oth er
O-H
4-Hyd roxypentanal
1
4
O
H
C
H
O
H
O-H
O
A cyclic hemiacetal
Haworth Projections

D-Glucose forms these cyclic hemiacetals
1
CHO
H
OH
HO
H
H
H
red raw to sh ow th e -OH
on carbon-5 close to the
aldeh yd e on carbon-1
OH
5
OH
H
CH2 OH
D -Glucose
CH 2 OH
5
OH
H
O
H
OH H C1
HO
H
CH2 OH
O OH (  )
H
H
OH H
HO
H
H OH
-D -Glucopyranose
(-D -Glucose)
OH
CH2 OH anomeric
carb on
OH
H
H
+
OH H
HO
OH(  )
H OH
-D -Glucopyranose
( -D -Glucos e )
Haworth Projections





a five- or six-membered cyclic hemiacetal is
represented as a planar ring
groups lie either above or below the plane
the new carbon stereocenter is called an
anomeric carbon
stereoisomers that differ in configuration
only at the anomeric carbon are called
anomers
the anomeric carbon of an aldose is C-1; that
of the most common ketoses is C-2
Haworth Projections

Terminology of carbohydrate chemistry,



 means that the anomeric -OH is on the same
side of the ring as the terminal -CH2OH
 means that the anomeric -OH is on the side of
the ring opposite the terminal -CH2OH
a six-membered hemiacetal ring is called a
pyranose, and a five-membered hemiacetal ring
is called a furanose
Haworth Projections


aldopentoses also form cyclic hemiacetals
the most prevalent forms of D-ribose and
other pentoses in the biological world are
furanoses
HOCH2
H
H
H
O
H
HOCH2
H
OH ()
O
H
OH ()
H
H
OH
OH
OH
H
-2-D eoxy-D -ribofuranose
-D -Ribofuranose
(-2-D eoxy-D -rib os e)
(-D -Rib os e)
Haworth Projections
D-fructose also forms a five-membered
cyclic hemiacetal

HOCH2
5
1
O
H HO
CH2 OH
2
OH( )
H
HO
H
 -D -Fructofuranose
( - D -Fructos e)
1
2
CH2 OH
C=O
HO
H
H
OH
H 5 OH
CH2 OH
D -Fru ctose
HOCH2
5
O
H HO
H
OH ( )
2
CH2 OH
HO
H
1
 - D -Fru ctofu ran os e
(- D -Fructose)
Mutarotation

Mutarotation: the equilibrium
interconversion of - and -anomers
in aqueous solution
Chair Conformations Pg 475

Lets leave this out. I will be
very happy if you can draw
Fisher and Hayworth forms.
Physical Properties

Monosaccharides are colorless crystalline
solids, very soluble in water

sweetness relative to sucrose:
S w eetness
Relative to
Carbohydrate
S ucrose
fructos e
1.74
sucrose (tab le sugar) 1.00
honey
0.97
glu cose
0.74
maltose
0.33
galactos e
0.32
lactose (milk su gar)
0.16
S w eetness
Relative to
Artificial
Sw eetener
S ucrose
saccharin
450
acesu lfame-K
200
aspartame
180
Chemical Properties

Monosaccharides

Hemiacetal into acetal – glycosidic bond



A glycosidic bond slows mutarotation to snails pace.
Acid is needed to break acetal or ketal
Aldose’s reduce Cu2+, Fe3+, and cold MnO4

Only works with the linear aldehyde form
Hemiacetals are in equilibrium with aldehyde form



Called reducing sugars
Glycosides cannot reduce these
Carbonyl can be reduced
Formation of Glycosides

Treatment of a monosaccharide with an
alcohol gives an acetal
anomeric
CH2 OH
carbon
O OH
H
+
H
H
+ CH3 OH
OH H
-H2 O
HO
H
glycos idic
H OH
CH2 OH
bond
-D -Glu copyran os e
O OCH3
H
(-D -Glu cose)
H
+
OH H
H
HO
CH2 OH
OH
H
H
OH H
HO
OCH3
H OH
H OH
Methyl -D -glu copyran os ide Methyl -D -glu copyran os ide
(Methyl -D -glu coside)
(Methyl -D -glucos ide)
Glycosides




a cyclic acetal derived of a
monosaccharide is called a glycoside
the bond from the anomeric carbon to the
-OR group is called a glycosidic bond
mutarotation is VERY SLOW in a
glycoside
glycosides are stable in water and
aqueous base, but like other acetals, are
hydrolyzed in aqueous acid to an alcohol
and a monosaccharide
Oxidation to Aldonic Acids



the aldehyde group of an aldose is oxidized under
basic conditions to a carboxylate anion
the oxidation product is called an aldonic acid
reducing sugar (it reduces the oxidizing agent)
H
O
C
HO
CH2 OH
O
HO
OH
OH
 - D -Glucopyranose
( - D -Glucos e)
H
HO
H
H
O-
O
C
OH oxidizin g
H
OH
agent
H
HO
H
OH
b asic
H
OH
OH solution
H
OH
CH2 OH
CH2 OH
D -Glu cose
D -Glu conate
Oxidation to Uronic Acids

Enzyme-catalyzed oxidation of the primary
alcohol at C-6 of a hexose yields a uronic acid

enzyme-catalyzed oxidation of D-glucose, for
example, yields D-glucuronic acid
CHO
enzymeH
OH
catalyzed
HO
H
oxidation
H
OH
H
OH
CH2 OH
D -Glu cose
H
HO
H
H
CHO
OH
H
OH
OH
COOH
COOH
HO
HO
D -Glucu ronic acid
(a u ronic acid )
O
OH
OH
Reduction to Alditols

The carbonyl group can be reduced to a
hydroxyl group by NaBH4 and H2/Pd

HO
HO
the reduction product is called an alditol
CH2 OH
O
OH
OH
-D -Glucop yranose
CHO
H OH
HO H
NaBH4
H OH
H OH
CH2 OH
D -Glu cose
CH2 OH
H OH
HO H
H OH
H OH
CH2 OH
D -Glucitol
(D -Sorbitol)
Reduction to Alditols



sorbitol is found in the plant world in many
berries and in cherries, plums, pears, apples,
seaweed, and algae
it is about 60 percent as sweet as sucrose
these three alditols are also common in the
biological world
CH OH
2
CH2 OH
H
OH
H
OH
CH2 OH
Erythritol
HO
HO
H
H
H
H
OH
OH
CH2 OH
D -Mannitol
CH2 OH
H
OH
HO
H
H
OH
CH2 OH
Xylitol
D-Glucuronic Acid



D-glucuronic acid exists in the plants and animals
in humans, it is an important component of the
acidic polysaccharides of connective tissues
it is used to detoxify foreign phenols and alcohols; in
the liver, these compounds are converted to
glycosides of glucuronic acid and excreted in the
urine
COOHO
HO
HO
O
O
OH
Propofol
A u rin e-s olu ble glucuronide
Phosphate Esters

Mono- and diphosphoric esters are intermediates
in metabolism of monosaccharides

the first step in glycolysis is conversion of D-glucose to
-D-glucose 6-phosphate
H
HO
H
D -Glucos e 6-phosp hate
H
CHO
OH
H
OH
OH O
CH2 O-P-O
O
O
O P O
O
CH2
HO
HO
O
HO
OH
Disaccharides

Sucrose


most abundant disaccharide
sucrose is a nonreducing sugar (why)
CH2 OH
OH
1
HO
HO
OH
HO
OH
O
O
HO 2
CH2 OH
1
OH
HOCH2
a unit of -D glu copyran os e
CH2 OH
O
HOCH2
O
HO
OH
1
O
a unit of -D fructofuranose
2
1
CH2 OH
Disaccharides

Lactose



lactose is the principal sugar present in milk
it consists of D-galactopyranose bonded by a -1,4glycosidic bond to carbon 4 of D-glucopyranose
lactose is a reducing sugar (why)
CH2 OH
OH
O
OH
CH2 OH
O
OH
4
OH
OH
CH2 OH
-1,4-glycosid ic bond
O
4
O
1
OH
OH
HO
1
OH
O
HO
CH2 OH
O
OH
OH
Disaccharides

Maltose



present in malt
two D-glucopyranose joined by an -1,4-glycosidic bond
maltose is a reducing sugar (Why)
1
HOCH2 O
HO
OH
CH2 OH
4
O
OH
OH
HO
O OH
HO
HO
-1,4-glycosid ic
b on d
CH2 OH
O
1
OH 4 CH2 OH
O
O
HO
OH
OH
Polysaccharides

Polysaccharide: lots of monosaccharide
units


Also called glycans
Can be  or  linked anomers


One we can digest “”
The other we cannot “”
Polysaccharides - 

Starch: an energy storage polymer of Dglucose found in plants



starch can be separated into amylose and
amylopectin
amylose is D-glucose units joined by -1,4-bonds
Amylopectin - D-glucose units joined by -1,4
bonds; at branch points, new chains every 24 to
30 units are started by -1,6-glycosidic bonds
Polysaccharides - 

Glycogen is the energy-reserve
carbohydrate for animals


glycogen - glucose units joined by -1,4- and
-1,6-glycosidic bonds (branches occur every
8 to 12 residues - more compact than starch)
the total amount of glycogen in the body of a
well-nourished adult human is about 350 g,
divided almost equally between liver and
muscle
Polysaccharides - 

Why Store sugar as starch or glycogen?

Osmolarity



Individual sugars would be 0.4 M
Polymers (mostly insoluable) 10-8 M
Cells would burst with water running into
the to equilibrate osmotic pressure!
Polysaccharides - 

Cellulose is a linear polysaccharide of Dglucose units joined by -1,4-glycosidic bonds




it has an average molecular weight of 400,000
g/mol, approximately 2200 glucose units
cellulose molecules act like stiff rods and align
themselves side by side into well-organized waterinsoluble fibers in which the OH groups hydrogen
bond with each other rather than water.
this arrangement of parallel chains in bundles gives
cellulose fibers their high mechanical strength
it is also the reason why cellulose is insoluble in
water
Polysaccharides - 

Cellulose (cont’d)

animals cannot digest cellulose




no contain -glucosidases, enzymes that catalyze
hydrolysis of -glucosidic bonds
we have only -glucosidases; hence we can digest
starch and glycogen
many bacteria and microorganisms have glucosidases and can digest cellulose
termites have such bacteria in their intestines
and can use wood as their principal food
Acidic Polysaccharides

Acidic polysaccharides: contain carboxyl
groups and/or sulfuric ester groups


play important roles in the structure and function
of connective tissues
there are a large number of highly specialized
forms of connective tissue


such as cartilage, bone, synovial fluid, skin, tendons,
blood vessels, intervertebral disks, and cornea
most connective tissues are made up of collagen,
a structural protein, in combination with a variety
of acidic polysaccharides
Acidic Polysaccharides

Hyaluronic acid

Found in embryonic tissues, synovial fluid,
lubricant of joints in the body, and the
vitreous of the eye
D -glucu ronic acid
N-Acetyl-D -glu cosamine
-
4
HO
COO
4
O HO
O
1
CH2 OH
O
1
3
NH
C
H3 C
O
The rep eating unit of h yalu ronic acid
3
OH
O
Acidic Polysaccharides

Heparin: a heterogeneous mixture of variably
sulfonated polysaccharide chains, ranging in
molecular weight from 6,000 to 30,000 g/mol
N -acetyl-D -glu cos amin e
OSO3
CH2
O
HO
D -glucuronic acid
-
D -glucosamine
O
NH
O C O
HO
CH3
OH
CH2
-
COO
O
O
OH - O S
3
L-id uronic acid
D -glucosamine
O
O
NH
O
SO3 - HO
O
O
HO
COO- OSO 3
OSO3 CH2
O
NH
O
SO3 -
Acidic Polysaccharides

Heparin (cont’d)



heparin is synthesized and stored in mast
cells of various tissues, particularly the
liver, lungs, and gut
the best known and understood of its
biological functions is its anticoagulant
activity
it binds strongly to antithrombin III, a
plasma protein involved in terminating the
clotting process
Carbohydrates
End
Chapter 19