1. 16 16-1 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Introduction to Organic Chemistry 2 ed William H. Brown

2. 16 16-2 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Carbohydrates Chapter 24 Chapter 16

3. 16 16-3 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Carbohydrates Carbohydrate Carbohydrate: a polyhydroxyaldehyde or polyhydroxyketone, or a substance that gives these compounds on hydrolysis Monosaccharide Monosaccharide: a carbohydrate that cannot be hydrolyzed to a simpler carbohydrate C n H 2n O n n monosaccharides have the general formula C n H 2n O n, where n varies from 3 to 8 aldose aldose: a monosaccharide containing an aldehyde group ketose ketose: a monosaccharide containing a ketone group

4. 16 16-4 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Monosaccharides monosaccharides are classified by their number of carbon atoms

5. 16 16-5 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 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. 16 16-6 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Monosaccharides Glyceraldehyde contains a stereocenter and exists as a pair of enantiomers

7. 16 16-7 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Fischer Projections Fischer projection 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. 16 16-8 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. D,L Monosaccharides In 1891, Emil Fischer made the arbitrary assignments of D- and L- to the enantiomers of glyceraldehyde

9. 16 16-9 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. D,L Monosaccharides According to the conventions proposed by Fischer D-monosaccharide D-monosaccharide: a monosaccharide that, when written as a Fischer projection, has the -OH on its penultimate carbon on the right L-monosaccharide L-monosaccharide: a monosaccharide that, when written as a Fischer projection, has the -OH on its penultimate carbon on the left

10. 16 16-10 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Following are the two most common D-aldotetroses and the two most common D-aldopentoses D,L Monosaccharides

11. 16 16-11 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. D,L Monosaccharides and the three most common D-aldohexoses

12. 16 16-12 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 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 anomeric carbon: the new stereocenter resulting from cyclic hemiacetal formation anomers anomers: carbohydrates that differ in configuration at their anomeric carbons

13. 16 16-13 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 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 -CH 2 OH;  - means that it is trans

14. 16 16-14 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.

15. 16 16-15 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Haworth Projections pyran six-membered hemiacetal rings are shown by the infix -pyran- furan five-membered hemiacetal rings are shown by the infix -furan-

16. 16 16-16 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Conformational Formulas five-membered rings are close to being planar so that Haworth projections are adequate to represent furanoses

17. 16 16-17 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Conformational Formulas for pyranoses, the six-membered ring is more accurately represented as a strain-free chair conformation

18. 16 16-18 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Conformational Formulas compare the orientations of groups on carbons 1-5 in the Haworth and chair representations of  -D-glucopyranose in each case they are up-down-up-down-up

19. 16 16-19 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Mutarotation Mutarotation Mutarotation: the change in specific rotation that occurs when the  or  forms of a carbohydrate are converted to an equilibrium mixture of the two

20. 16 16-20 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.

21. 16 16-21 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Physical Properties monosaccharides are colorless crystalline solids, very soluble in water, but only slightly soluble in ethanol following are relative sweetnesses (table sugar = 100 is the reference sweetness)

22. 16 16-22 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Formation of Glycosides Glycoside Glycoside: a carbohydrate in which the -OH of the anomeric carbon is replaced by -OR Methyl  -D-glucopyranoside (methyl  -D-glucoside)

23. 16 16-23 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Glycosides Glycoside bond Glycoside bond: the bond from the anomeric carbon of the glycoside to an -OR group eide 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. 16 16-24 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. N-Glycosides The anomeric carbon of a cyclic hemiacetal 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. 16 16-25 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. N-Glycosides

26. 16 16-26 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Reduction to Alditols The carbonyl group of a monosaccharide can be reduced to an hydroxyl group by a variety of reducing agents, including NaBH 4 and H 2 /M

27. 16 16-27 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Oxidation to Aldonic Acids Oxidation of the -CHO group of an aldose to a - CO 2 H group can be carried out using Tollens’, Benedict’s, or Fehling’s solutions

28. 16 16-28 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Oxidation to Aldonic Acids 2-Ketoses are also oxidized by these reagents because, under the conditions of the oxidation, 2-ketoses equilibrate with isomeric aldoses

29. 16 16-29 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 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 arises because of the high incidence of diabetes in the population

30. 16 16-30 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Glucose Assay The glucose oxidase method is completely specific for D-glucose

31. 16 16-31 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Glucose Assay O 2 is reduced to hydrogen peroxide H 2 O 2 the concentration of H 2 O 2 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

32. 16 16-32 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Ascorbic Acid (Vitamin C) L-Ascorbic acid (vitamin C) is synthesized both biochemically and industrially from D-glucose

33. 16 16-33 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Ascorbic Acid (Vitamin C) L-ascorbic acid is very easily oxidized to L- dehydroascorbic acid. both compounds are physiologically active and are found in most body fluids

34. 16 16-34 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Maltose From malt, the juice of sprouted barley and other cereal grains

35. 16 16-35 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.  -Maltose

36. 16 16-36 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Lactose The principle sugar present in milk about 5% - 8% in human milk, 4% - 5% in cow’s milk

37. 16 16-37 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.  -Lactose

38. 16 16-38 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Sucrose Table sugar, from the juice of sugar cane and sugar beet

39. 16 16-39 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Blood Group Substances Membranes of animal plasma cells have large numbers of relatively small carbohydrates bound to them antigenic determinants these membrane-bound carbohydrates are part of the mechanism by which cell types recognize each other; they act as antigenic determinants blood group substances among the first discovered of these antigenic determinants are the blood group substances

40. 16 16-40 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. ABO Blood Classification In the ABO system, individuals are classified according to four blood types: A, B, AB, and O at the cellular level, the biochemical basis for this classification is a group of relatively small membrane- bound carbohydrates

41. 16 16-41 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. ABO Blood Classification

42. 16 16-42 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. L-Fucose L-fucose is synthesized biochemically from D- glucose (see Problem 24.32)

43. 16 16-43 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 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 amylose is composed of continuous, unbranched chains of up to 4000 D-glucose units joined by  -1,4-glycoside bonds amylopectin amylopectin is a highly branched polymer of D- glucose. Chains consist of 24-30 units of D-glucose joined by  -1,4-glycoside bonds and branches created by  -1,6-glycoside bonds

44. 16 16-44 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Glycogen The reserve carbohydrate for animals 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

45. 16 16-45 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 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, corresponding to approximately 2800 D-glucose units per molecule Both rayon and acetate rayon are made from chemically modified cellulose

46. 16 16-46 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Carbohydrates End Chapter 16