Chemistry 102
Lecture 18: Carbohydrate Intro, Monosaccharides, Cyclization of
Monosaccharides
Sections 18.1-18.3 in Blei & Odian 2nd edition
05/13/08
HW#3 is Chapter 18: 14, 20, 26, 32, 42, 44; Chapter 19: 6, 10, 16, 18, 38, 48
Carbohydrates
18.1: Introduction
“Carbohydrate” is an archaic term. Are sugars really hydrates of carbon?
Cn(H2O)m
You could write glucose’s molecular formula C6H12O6 as C6(H2O)6, but the
structure really isn’t one of a simple hydrate (like MgSO47H2O)
CH2OH
OH
O
OH
OH
OH
Even though sugars are not simple hydrates of carbon, the term helps us
interpret their properties:
 Glucose solubility = 1 gm/mL H2O
o Pretty good for an organic molecule of MW = 180
o Syrup!
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The term saccharide, from L. saccarum, meaning sugar – is used for smaller
carbohydrates that give a sweet sensation
Biologic uses of carbohydrates:
 Energy
 Structure
 Cellular Recognition
 Information Storage Transfer
18.2: Monosaccharides
Structure and Nomenclature

Sugars end with –ose

Families of sugars are indicated by the number of C’s

Sugars are either aldoses or ketoses
o Aldose
o Ketose
Problem: Below is the Fischer projection for glucose. Classify it in terms of
the number of carbons and whether it is an aldehyde or a ketone. For
example, D-glyceraldehyde is an aldotriose
CHO
H
CHO
H
HO
OH
H
OH
H
OH
CH2OH
H
OH
D-glyceraldehyde
CH 2OH
D-glucose
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We will be particularly interested in the following monosaccharides

D-glyceraldehyde (D-aldotriose)

D-ribose (D-aldopentose)

D-glucose (D-aldohexose)

D-galactose (D-aldohexose)

D-fructose (D-ketohexose)
D vs. L Monosaccharides & Fischer Projections
CHO
H
CHO
OH
H
CH2OH
OH
CH2OH
(R)-glyceraldehyde
D-glyceraldehyde
Question: Is there any difference between (R)-glyceraldehyde and Dglyceraldehyde?
Question: D-glyceraldehyde in 100 % enantiomeric excess rotates plane
polarized light +13.5o. What would the rotation of plane polarized light for
L-glyceraldehyde in 100 % enantiomeric excess?
Fischer and Haworth projections for

D-ribose (D-aldopentose)
CHO
H
OH
H
OH
H
OH
CH 2OH
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
D-glucose (D-aldohexose)
CHO
H
HO
OH
H
H
OH
H
OH
CH 2OH

D-fructose (D-ketohexose)
CH2OH
O
HO
H
H
OH
H
OH
CH2OH

D-galactose (D-aldohexose)
CHO
H
OH
HO
H
HO
H
H
OH
CH 2OH
Question: What makes each of the above a “D” monosaccharide?
Question: Are fructose and glucose isomers of one another?
Question: Are glucose and galactose enantiomers of one another?
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Amino Sugars
CHO
H
CHO
NH2
HO
H
CHO
NH2
H
N
H
O
H
HO
H
HO
H
OH
HO
H
H
OH
H
OH
H
OH
H
OH
CH2OH
CH2OH
CH2OH
galactosamine
glucosamine
N-acetyl glucosamine
18.3: The Cyclic Structure of Monosaccharides
Hemiacetals vs acetals – cyclic monosaccharides vs. polysaccharides:
Glucose:
Glucose hemiacetal formation
CH2OH
CH2OH
OH
OH
OH
O
O
OH
OH
OH
OH
OH
Acetal formation between 2 glucose molecues
CH2OH
OH
O
OH
CH2OH
OH
OH
O
OH
H+
OH
OH
OH
CH2OH
CH2OH
O
O
OH
OH
+
O
OH
OH
OH
H2O
OH
It is important to recognize which positions are “fixed” and which can
change absolute configuration – look for the hemiacetal motif and recall the
equilibrium between hemiacetal and aldehydes + alcohol
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The anomeric C:  and  designation
Note that cyclized glucose is a pyranose (6C oxygen containing ring)
Conformational representation of glucose (or how to remember the absolute
configuration of substituents in cyclized glucose): with the anomeric carbon
in the  configuration, all of the groups are “trans” to each other
Fructose:
Note that cyclized fructose is a furanose (5C oxygen containing ring)
Ribose:
Examine the Fischer projection of ribose – do you expect it to be a furanose
or pyranose?
Mutarotation:
Pure -D-glucose = +112o  +57o at equilibrium
Pure -D-glucose = +18.7o  +57o at equilibrium
Question: Which of the 2 conformations do you expect to be more stable?
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+57o corresponds to 64% -D-glucose and 36% -D-glucose; only .003% is in
open chain form, but this is enough to make hemiacetals reactive – they are
reducing sugars
The osmotic diuretics mannitol and sorbitol:
CH2OH
CHO
H
HO
CH2OH
OH
HO
H
H
H
HO
H
HO
OH
H
H
OH
H
OH
H
OH
H
OH
H
OH
H
OH
CH2OH
glucose
CH2OH
mannitol
CH2OH
sorbitol
Question: Do you expect sorbitol to undergo mutarotation?
Glucose, sorbitol, aldose reductase, and diabetic cataract formation:
Sorbitol as a sugar substitute for diabetics
Warning: be careful how much sugarless candy you eat!
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Chemistry 102
Lecture 19: Physical and Chemical Properties of Monosaccharides, Disaccharides
Sections 18.4-18.5 in Blei & Odian 2nd edition
05/14/08
18.4: Characteristic Reactions of Monosaccharides
Glycoside Formation
Synonomous with acetal formation; we can “lock” the cyclic form in place by
further reacting a hemiacetal with an alcohol functional group in an acid
environment
CH2OH
OH
O
CH2OH
OH
H+
OH
OH
O
+
O CH3
OH
OH
OH
HOCH3
CH2OH
OH
CH2OH
O
H+
OH
OH
OH
H2O
OH
O
O CH3
+
H2O
OH
OH
The above is glucose being converted to methyl  and -D-glucoside
 The glycosidic bond is from the anomeric C to the OCH3 (methoxy)
group
 This is the same type of reaction that occurs when
monosaccharides are converted to disaccharides
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Oxidation of the Aldehyde Group:
Benedict’s reagent is Cu+2 complexed with the tricarboxylic acid citrate (of
citric acid fame) in alkaline solution:
oxidized
O
Sugar
O
+ Cu+2
Sugar
H
Open Chain
reduced
Cu2O
+
OH
Rusty Red
Blue
Oxidation to Uronic Acids:
OH
OH
O
CH2OH
O
2 NAD+
OH
O-UDP
OH
UDPG Dehydrogenase
OH
O
O-UDP
OH
OH
 The enzyme that oxidizes glucose to glucuronic acid recognizes
glucose when linked to uridine diphosphate
o Interestingly, this is the form used to make glycogen when
there is lot’s of glucose around
 Glucuronic acid linked to N-acetyl glucosamine forms hyaluronic acid,
an important component of connective tissue
 Glucuronic acid links to non-polar compounds to remove them from the
body; an interesting example is the removal of estradiol:
OH
HO
Estradiol
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18.5: Disaccharides
 Disaccharide: 2 Monosaccharides linked via a glycosidic bond
 Oligosaccharide: 6-10 monosaccharides linked by glycosidic bonds
 Polysaccharide: large numbers of monosaccharides linked by glycosidic bonds
Maltose:
2 glucose linked via an -1,4-glycosidic linkage
Question: Is maltose a reducing sugar?
Sucrose:
-D-glucose joined to -D-fructose via an -1,2-glycosidic linkage
Question: Is sucrose a reducing sugar?
Lactose:
-D-galactose joined to D-glucose via an -1,4-glycosidic linkage
Question: Is lactose a reducing sugar?
Question: Amylose is a linear polysaccharide that may contain several
thousand glucose monomers. Is it a reducing sugar?
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Chemistry 102
Lecture 20: Polysaccharides
Sections 18.6 in Blei & Odian 2nd edition
05/15/08
18.6: Polysaccharides
Poly  many
Saccharum  sugar
Starch
Starch = Amylose + Amylopectin
Amylose is unbranched: glucose connected by -1,4-glycosidic linkages
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Amylopectin is a branched polysaccharide: glucose connected by -1,4glycosidic linkages + -1,6-glycosidic linkages
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Glycogen is also branched via -1,6-glycosidic linkages, only to a greater
extent than amylopectin. In the cartoon below, amylopectin is on the left,
glycogen on the right
Glycogen
Glycogen is the major mammalian storage form of glucose.

Ca. 106 units of glucose (like amylopectin)

Ca. 350 g in well nourished individual, split between liver and
muscle)
Question: How many glycogen molecules are there in a well nourished adult?
Question: Given that glucose can only be utilized by taking a glucose off of
the end of an -1,4 linked polysaccharide, does it make sense that glycogen
is more highly branched than amylopectin?
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Cellulose
Cellulose is also unbranched: glucose connected by -1,4-glycosidic linkages
Again, structure is driven by hydrogen bonding; only in this case, optimal Hbonding leads to tremendous interactions between cellulose polymers
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Cellulose microfibrils orient perpendicular to one another in the formation of
the plant cell wall and are cemented with hemicellulose and pectin
 Pectin is primarily -1,4 linked galactouronic acid and is a principal
soluble dietary fiber
 Average molecular weight of cellulose = 4 x 105 or 2,200 glucose units
Question: What is the overriding structural feature that governs the
physical properties of carbohydrates?
Question: Would cellulose be a soluble or insoluble fiber?
Question: Why do paper towels work well absorbing both aqueous and oily
spills?
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An example of a polysaccharide in drug formulation: xanthan gum:
 Bacterial fermentation product
 Usually about 7000 monomers/polymer
 Used as a matrix forming agent; i.e., upon contact with water
forms a hydrated gel that remains sufficiently intact to control
drug release
Question: What is the fundamental basis for “preservatives” in terms of the
physical properties of sugars?
Acidic Polysaccharides
Acidic polysaccharides contain amino sugars, so it is more usual to refer to
them as glycosaminoglycans.
Together with the structural protein collagen, they form a large number of
connective tissues
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Hyaluronic acid

Repeating units of glucuronic acid bonded to N-acetyl-glucosamine via
a -1,3-glycosidic linkage, with the N-acetyl-glucosamine bonded to
the next glucuronic acid via an -1,4-glycosidic bond
o Recall an amino group replaces the hydroxyl at C2 in
glucosamine

3 x 102 to 1 x 105 units, depending on origin

Adds as a shock absorber for cartilage
Question: Why can individuals take glucosamine as the HCl or sulfate salt
when hyaluronic acid is made of N-acetyl-glucosamine?
Perhaps we should eat more bugs for the chitin content: N-acetylglucosamine with -1,4-glycosidic linkages
Heparin
 Variably sulfated polysaccharide chains
 MW 6,000 to 30,000
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 Major clinical anticoagulant, also produced and stored by mast cells
in the body (which makes sense when you consider the need to
recruit cells into areas of inflammation)
 Inhibits many proteins in the coagulation cascade
Not to be confused with hirudin, a protein that binds directly to thrombin
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