1. Copyright © 2014 by John Wiley & Sons, Inc. All rights reserved.
Chapter 22
Carbohydrates
Created By
Prof. Gary F. Porter, Ph.D.
Copyright © 2014 by John Wiley & Sons, Inc. All rights reserved.

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Table of Contents
Introduction
Monosaccharides
Mutarotation
Glycosidic Formation
Other Reactions of Monosaccharides
Oxidation Reactions of Monosaccharides
Reduction of Monosaccharides: Alditols
Reactions of Monosaccharides with Phenylhydrazine: Osazone
Synthesis of Monosaccharides
Degradation of Monosaccharides
11. The D Family of Aldoses
12. Disaccharides
13. Polysaccharides
14. Other Biologically Important Sugars
15. Sugars that Contain Nitrogen
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1. Introduction
1a. Classification of Carbohydrates
Carbohydrates
Are polyhydroxyl aldehydes and ketones in the monomeric form and
Exist in hemiacetal and acetal forms.
Sugars are
Monosaccharides - 1 monomeric unit
Disaccharides - 2 monomeric units)
Oligosaccharides - 3 to 10 monomeric units
Polysaccharides - more than 10 monomeric units
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2. Monosaccharides
2A. Classification of Monosaccharides
Aldose - contains an aldehyde group
Ketose - contains a ketone group
Triose - contains 3 carbons
Tetrose - contains 4 carbons
Aldopentose - contains an aldehyde & 5 carbons
Ketohexose - contains a ketone & 6 carbons
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5. 2A. Classification of Monosaccharides
Practice Problem 22.1
How many chirality centers are contained in (a) the aldotetrose and (b) the ketopentose above? (c) How many stereoisomers would you expect from each general structure?
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2. Monosaccharides
2B. D- and L- Designations of Monosaccharides Identify the molecule which has a chirality center.
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2. Monosaccharides
2B. D- and L- Designations of Monosaccharides
Two enantiomeric forms of glyceraldehyde exist. We designate D- and L- for these trioses.
D-Form L-Form
Note: These designations give no indication of their dexo- vs. levorotatory nature.
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2. Monosaccharides
2B. D- and L- Designations of Monosaccharides
Note which carbon determines the D- & L- designations
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9. 2B. D- and L- Designations of Monosaccharides
Practice Problem 22.2
Identify a three-dimensional formula for the above and designate each as a D- or L- sugar.
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10. 2C. Structural Formulas for Monosaccharides
Fischer projections are useful for monosaccharide analysis.
Note the two orientations of the blue oxygens below.
Haworth formulas are useful because monosaccharides exist in the cyclic form.
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11. 2C. Structural Formulas for Monosaccharides
Formulas 6 and 7 illustrate the three-dimensional configurations of the molecules.
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12. 2C. Structural Formulas for Monosaccharides
These diastereomers
Differ only at the hemiacetal carbon, and
Are the α and β anomers of D-glucose.
Ketoses form cyclic acetals with the same two anomeric forms.
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3. Mutarotation
The α and β anomers are in equilibrium. The value of that equilibrium is the mutarotation value.
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3. Mutarotation
This equilibrium favors the more stable β anomer.
This shift in equilibrium is called the anomeric effect.
Note: The open-chair form is negligible at equilibrium.
This equilibrium favors the more stable α anomer.
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4. Glycosidic Formation
Formation of glycosidic bonds are
Acid-catalyzed and
Include the addition of methanol.
Note: The acid catalyzed addition of methanol on salicin produces aspirin.
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4. Glycosidic Formation
Hydrolysis of a glycosidic bond
Does not react in base, and
Is acid-catalyzed.
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5. Other Reactions of Monosaccharides
5A. Enolization, Tautomerization, and Isomerization
Base facilitates isomerization of monosaccharides.
Enolization creates epimers.
D-Glucose to D-Mannose
Tautomerization creates structural isomers.
D-Glucose to D-Fructose
Note: Formation of a glysoside prevents enolization.
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5. Other Reactions of Monosaccharides
5A. Enolization, Tautomerization, and Isomerization
Tautomerization creates structural isomers
D-Glucose to D- Fructose
Note: Formation of a glycoside prevents enolization
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5. Other Reactions of Monosaccharides
5C. Formation of Ethers
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5. Other Reactions of Monosaccharides
5C. Formation of Ethers
Exhaustive Methylation
SN2 Mechanism
Base-catalyzed
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5. Other Reactions of Monosaccharides
5D. Conversions to Esters
Base-catalyzed with pyridine or sodium acetate
Treat with excess acetic anhydride
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5. Other Reactions of Monosaccharides
5E. Conversion to Cyclic Acetals
Are acid-catalyzed (H2SO4),
Needs vicinal (adjacent) hydroxyls,
Produces acetonides from acetone.
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6. Oxidation Reactions of Monosaccharides
Benedict’s Reagent: Reducing Sugars
Aldoses & Ketose are reducing sugars.
Anomeric methylated Aldoses & Ketoses are non-reducing sugars.
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24. 22.6 Oxidation Reactions of Monosaccharides
Benedict’s Reagent: Reducing Sugars
Gives a positive test for Aldoses & Ketoses, and
Gives a negative test for Non-reducing sugars.
22.6 Oxidation Reactions of Monosaccharides
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6. Oxidation Reactions of Monosaccharides
Tollens’ Reagent: Reducing Sugars
(Aldoses vs. Ketoses)
Gives a positive test for Aldoses, and
Gives a negative test for Ketoses.
Aldehyde + Ag+(NH3)2HO- Carboxylate + Ag(↓)
Clear Soln. Mirrored Silver Surface
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6. Oxidation Reactions of Monosaccharides
Practice Problem 22.6 How might you distinguish between α-D-glucopyranose (i.e., D-glucose), methyl α-D-glucopyranoside, and α-D-fructofuranose.
Sugars
Benedict's Test
Tollens’ Test
α-D-glucopyranose
Pos. or Neg.
Me α-D-glucopyranoside
α-D-fructofuranose
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6. Oxidation Reactions of Monosaccharides
6B. Bromine Water:
The Synthesis of Aldonic Acid
Selectively oxidizes Aldehydes,
Gives a positive Test for Aldose,
and
Gives a negative test for Ketose.
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6. Oxidation Reactions of Monosaccharides
6C. Nitric Acid Oxidation: Aldaric Acids
Oxidizes both –CHO and –CH2OH groups,
Forms –COOH groups.
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6. Oxidation Reactions of Monosaccharides
6D. Periodate Oxidations: Oxidative Cleavage of Polyhydroxyl Compounds
Mechanism
Stoichiometric cleavage
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6. Oxidation Reactions of Monosaccharides
6D. Periodate Oxidations: Oxidative Cleavage of Polyhydroxyl Compounds
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6. Oxidation Reactions of Monosaccharides
Practice Problem 22.9
What products would you expect to be formed when each of the following compounds is treated with an appropriate amount of periodic acid? How many molar equivalents of HIO4 would be consumed in each case?
Practice Problem 22.10
Show how periodic acid could be used to distinguish between an aldohexose and a ketohexose. What products would you obtain from each, and how many molar equivalents of HIO4 would be consumed?
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7. Reduction of Monosaccharides: Alditols
Reduction with NaBH4
Practice Problem 22.11
(a) Would you expect D-glucitol to be optically active? (b) Write Fischer projection formulas for all of the D-aldohexoses that would yield optically inactive alditols.
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8. Reactions of Monosaccharides with
Phenylhydrazine: Osazone
Osazone
The product is called a phenylasozone.
Substitutions occur on C-1 and C-2.
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8. Reactions of Monosaccharides with
Phenylhydrazine: Osazone
Epimers
Differ in chirality at a single carbon.
i.e., D-Glucose & D-Mannose
Osazone Formation
Results in loss of chirality at C2.
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9. Synthesis of Monosaccharides
Kiliani-Fischer Synthesis:
Carbons in sugar chain are lengthened.
Epimers are produced.
Practice Problem 22.13
Cyanohydrin
Hydrolysis
Lactone forms
(a) What are the structures of L-(+)-threose and L-(+)-erythrose? (b) What aldotriose would you use to prepare them in a Kiliani–Fischer synthesis?
Reduction
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10. Degradation of Monosaccharides
The Ruff Degradation:
Reduces the carbon chain by one carbon, and
Is an oxidative decarboxylation.
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The D Family of Aldoses
Most naturally occurring aldoses belong to the D-family
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Disaccharides
12A. Sucrose
Is ordinary table sugar.
Is found in photosynthetic plants.
Glucose
(as an α-pyranose)
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Disaccharides
12B. Maltose
Is a hydrolysis product from starch.
Glucose
(as an α-pyranose)
Glucose
(as an α-pyranose)
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Disaccharides
12C. Cellobiose
Is a hydrolysis product from cellulose.
Glucose
(as an α-pyranose)
Glucose
(as an α-pyranose)
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Disaccharides
12D. Lactose
Is present in mammalian milk.
Galactose
(as an α-pyranose)
Glucose
(as an α-pyranose)
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Polysaccharides
Polysaccharides are sugar units that are linked by glycosidic (acetal) bonds.
Homopolysaccharides
Are polymers with a single type of monosaccharide,
With glucose monomeric units are glucans, and
With galactose monomeric units are galactans.
Heteropolysaccharides
Are polymers containing more than one type of monosaccharide building block.
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Polysaccharides
13A. Starch
Is found in plants.
Stores glucose for energy.
All α-links.
Amylose = Linear structure.
Amylopectin = Branched structure.
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Polysaccharides
13B. Glycogen
Is found in animals.
Stores glucose for energy.
Has more α (1→6) branching than starch
Branched structure only.
All α-links.
α-1,4 chains with α-1,6 branch points.
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Polysaccharides
13C. Cellulose
Is found in plants.
Is a structural sugar.
All β-links.
Linear structure only.
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Other Biologically Important Sugars
Ribose and 2-Deoxyribose are
Found in RNA and DNA respectively.
Uronic Acids found in sulfonated polysaccharide called heparin.
Heparin is important in controlling blood clotting.
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15. Sugars that Contain Nitrogen
15A. Glycosamine
Anomeric hydrogens are replaced by nitrogen.
Nucleoside has Ribose and 2-Deoxyribose bonded to a nitrogenous ring system.
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15. Sugars that Contain Nitrogen
15B. Amino sugars have non-anomeric hydrogens replaced by nitrogen.
β-D-glucosamine is found in chitin.
NAG & NAM is found in bacterial cell walls.
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49.  END OF CHAPTER 22  Ch 49