1. William H. Brown & Christopher S. Foote
Organic Chemistry
William H. Brown & Christopher S. Foote

2. Carbohydrates
Chapter 25
Chapter 24

3. Carbohydrates
Carbohydrate: a polyhydroxyaldehyde or polyhydroxyketone, or a substance that gives these compounds on hydrolysis
Monosaccharide: a carbohydrate that cannot be hydrolyzed to a simpler carbohydrate
they have the general formula CnH2nOn, where n varies from 3 to 8
aldose: a monosaccharide containing an aldehyde group
ketose: a monosaccharide containing a ketone group

4. Monosaccharides
Monosaccharides are classified by their number of carbon atoms

5. Monosaccharides There are only two trioses
often aldo- and keto- are omitted and these compounds are referred to simply as trioses; although this designation does not tell the nature of the carbonyl group, it at least tells the number of carbons

6. Monosaccharides
Glyceraldehyde contains a stereocenter and exists as a pair of enantiomers

7. Fischer Projections
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

8. D,L Monosaccharides
In 1891, Emil Fischer made the arbitrary assignments of D- and L- to the enantiomers of glyceraldehyde

9. D,L Monosaccharides According to the conventions proposed by Fischer
D-monosaccharide: a monosaccharide that, when written as a Fischer projection, has the -OH on its penultimate carbon on the right
L-monosaccharide: a monosaccharide that, when written as a Fischer projection, has the -OH on its penultimate carbon on the left

10. D,L Monosaccharides
Here are the two most common D-aldotetroses and the two most common D-aldopentoses

11. D,L Monosaccharides
And the three common D-aldohexoses

12. Physical Properties
Monosaccharides are colorless crystalline solids, very soluble in water, but only slightly soluble in ethanol
sweetness relative to sucrose:

13. Cyclic Structure
Monosaccharides have hydroxyl and carbonyl groups in the same molecule and exist almost entirely as five- and six-membered cyclic hemiacetals
anomeric carbon: the new stereocenter resulting from cyclic hemiacetal formation
anomers: carbohydrates that differ in configuration at their anomeric carbons

14. Haworth Projections Haworth projections
five- and six-membered hemiacetals are represented as planar pentagons or hexagons, as the case may be, viewed through the edge
most commonly written with the anomeric carbon on the right and the hemiacetal oxygen to the back right
the designation - means that -OH on the anomeric carbon is cis to the terminal -CH2OH; - means that it is trans

15. Haworth Projections

16. Haworth Projections
six-membered hemiacetal rings are shown by the infix -pyran-
five-membered hemiacetal rings are shown by the infix -furan-

17. Conformational Formulas
five-membered rings are so close to being planar that Haworth projections are adequate to represent furanoses

18. Conformational Formulas
for pyranoses, the six-membered ring is more accurately represented as a strain-free chair conformation

19. Conformational Formulas
if you compare the orientations of groups on carbons 1-5 in the Haworth and chair projections of -D-glucopyranose, you will see that in each case they are up-down-up-down-up respectively

20. Mutarotation
Mutarotation: the change in specific rotation that occurs when an  or  form of a carbohydrate is converted to an equilibrium mixture of the two

21. Mutarotation

22. Formation of Glycosides
Glycoside: a carbohydrate in which the -OH of the anomeric carbon is replaced by -OR
methyl -D-glucopyranoside (methyl -D-glucoside)

23. Glycosides
Glycosidic bond: the bond from the anomeric carbon of the glycoside to an -OR group
Glycosides are named by listing the name of the alkyl or aryl group attached to oxygen followed by the name of the carbohydrate with the ending -e replaced by -ide
methyl -D-glucopyranoside
methyl -D-ribofuranoside

24. N-Glycosides
The anomeric carbon of a cyclic hemiacetal also undergoes reaction with the N-H group of an amine to form an N-glycoside
N-glycosides of the following purine and pyrimidine bases are structural units of nucleic acids

25. N-Glycosides

26. Reduction to Alditols
The carbonyl group of a monosaccharide can be reduced to an hydroxyl group by a variety of reducing agents, including NaBH4 and H2/M

27. Oxidation to Aldonic Acids
The -CHO group can be oxidized to -COOH

28. Oxidation to Aldonic Acids
among the mild oxidizing agents used for this purpose is Tollens’ solution; if the test is done properly, silver metal precipitates as a silver mirror

29. Oxidation to Aldonic Acids
2-Ketoses are also oxidized by these reagents
under the conditions of the oxidation, 2-ketoses equilibrate with isomeric aldoses

30. Oxidation to Uronic Acids
Enzyme-catalyzed oxidation of the terminal -OH group gives a -COOH group

31. Oxidation by HIO4
Periodic acid cleaves the C-C bond of a glycol

32. Oxidation by HIO4
it also cleaves -hydroxyaldehydes

33. Oxidation by HIO4
and -hydroxyketones

34. Oxidation by HIO4
Oxidation of methyl -D-glucoside consumes 2 moles of HIO4 and produces 1 mole of formic acid, which indicates 3 adjacent C-OH groups

35. Oxidation by HIO4
this is evidence that methyl -D-glucoside is a pyranoside

36. Glucose Assay
The analytical procedure most often performed in the clinical chemistry laboratory is the determination of glucose in blood, urine, or other biological fluid
this need stems from the high incidence of diabetes in the population

37. Glucose Assay
The glucose oxidase method is completely specific for D-glucose

38. Glucose Assay the enzyme glucose oxidase is specific for -D-glucose
molecular oxygen, O2, used in this reaction is reduced to hydrogen peroxide H2O2
the concentration of H2O2 is determined experimentally, and is proportional to the concentration of glucose in the sample
in one procedure, hydrogen peroxide is used to oxidize o-toluidine to a colored product, whose concentration is determined spectrophotometrically

39. Ascorbic Acid (Vitamin C)
L-Ascorbic acid (vitamin C) is synthesized both biochemically and industrially from D-glucose

40. Ascorbic Acid (Vitamin C)
L-Ascorbic acid is very easily oxidized to L-dehydroascorbic acid. Both are physiologically active and are found in most body fluids

41. Maltose
From malt, the juice of sprouted barley and other cereal grains

42. Lactose The principle sugar present in milk
about 5 - 8% in human milk, 4 - 5% in cow’s milk

43. Sucrose
Table sugar, obtained from the juice of sugar cane and sugar beet

44. Starch Starch is used for energy storage in plants
it can be separated into two fractions; amylose and amylopectin; each on complete hydrolysis gives only D-glucose
amylose is composed of continuous, unbranched chains of up to 4000 D-glucose units joined by -1,4-glycoside bonds
amylopectin is a highly branched polymer of D-glucose. Chains consist of units of D-glucose joined by -1,4-glycoside bonds and branches created by -1,6-glycoside bonds

45. Glycogen Glycogen is the reserve carbohydrate for animals
like amylopectin, glycogen is a nonlinear polymer of D-glucose units joined by -1,4- and -1,6-glycoside bonds bonds
the total amount of glycogen in the body of a well-nourished adult is about 350 g (about 3/4 of a pound) divided almost equally between liver and muscle

46. Cellulose
Cellulose is a linear polymer of D-glucose units joined by -1,4-glycoside bonds
it has an average molecular weight of 400,000 g/mol, corresponding to approximately 2800 D-glucose units per molecule
both rayon and acetate rayon are made from chemically modified cellulose

47. Acidic Polysaccharides
Hyaluronic acid: an acidic polysaccharide present in connective tissue, such as synovial fluid and vitreous humor

48. Acidic Polysaccharides
Heparin
its best understood function is as an anticoagulant

49. Prob 25.11
Which are D-monosaccharides? Which are L-monosaccharides?

50. Prob 25.20
Convert each Haworth projection to an open-chain form and then to a Fischer projection. Name each monosaccharide.

51. Prob 25.21
Convert each chair conformation to an open-chain form and then to a Fischer projection. Name each monosaccharide.

52. Prob 25.24
Draw the cyclohexane ring in topiramate in its more stable chair conformation. Which groups are axial and which are equatorial? Draw the cyclic structure after hydrolysis of all amide, ester, and acetal bonds. Name the monosaccharide unit in topiramate.

53. Prob 25.30
One pathway for the metabolism of glucose is this enzyme-catalyzed reaction. Show that is can be regarded as two enzyme-catalyzed keto-enol tautomerizations.

54. Prob 25.31
Describe the type of reaction involved in each step in the biochemical synthesis of L-fucose.

55. Prob (cont’d)
Steps 4-5 are repeated here

56. Prob 25.38
Name the two monosaccharide units in trehalose. Is trehalose a reducing sugar? Does it undergo mutarotation?

57. Prob 25.39
Name the three monosaccharide units in raffinose.

58. Prob 25.40
From what monosaccharide is laetrile derived? Assign an R or S configuration to the stereocenter bearing the -CN group. Draw structural formulas for the products of hydrolysis of laetrile in aqueous acid.

59. Prob 25.43
Draw a chair conformation for the a- and b-pyranose forms of this monosaccharide and for the chair conformation of the disaccharide formed of joining two units of the pyranose form by a b-1,4-glycosidic bond.

60. Prob 25.44
(a) Alginic acid is a polymer of D-mannuronic acid in the pyranose form joined by b-1,4-glycosidic bonds. Draw the repeating unit.
(b) Pectic acid is a polymer of D-galacturonic acid in the pyranose form joined by a-1,4-glycosidic bonds. Draw the repeating unit.

61. Prob 25.45

62. Prob 25.46
Name each monosaccharide unit and describe each glycosidic bond.

63. Prob 25.49
Keratin sulfate is an important component of the cornea of the eye. From what monosaccharides is keratin sulfate derived? Describe the glycosidic bond.

64. Carbohydrates
End Chapter 25