Carbohydrates

1. Carbohydrates • Carbohydrate: a ________________ or ______________ , or a substance that gives these compounds on hydrolysis • Monosaccharide: a carbohydrate that cannot be _____________ 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

3. Fig 19.UN, p.472

4. d:\gob.exe Go to GOB slide 2 – classifying carbohydrates

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. Fig. 19.1, p.467

8. Fischer Projections • Fischer projection: a two dimensional representation for showing the configuration of tetrahedral __________________ • ____________ lines represent bonds projecting forward • vertical lines represent bonds projecting to the ______

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

10. 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 ___________ carbon on the right • L-monosaccharide: a monosaccharide that, when written as a Fischer projection, has the -OH on its penultimate carbon on the ______

11. D,L Monosaccharides • Following are the two most common D-aldotetroses and D-aldopentoses

12. D,L Monosaccharides • and the three common D-aldohexoses. Note that one of these is an amino sugar

13. Table 19.1, p.468

14. Table 19.2, p.469

15. Cyclic Structure • Monosaccharides have hydroxyl and carbonyl groups in the same molecule and exist almost entirely as five- and six-membered cyclic ______________ • __________ carbon: the new stereocenter resulting from cyclic hemiacetal formation • _______ : carbohydrates that differ in configuation at their anomeric carbons

16. Fig 19.UN, p.471

17. Fig 19.2, p.472

18. Haworth Projections • Haworth projections • five- and six-membered hemiacetals are represented as planar ________ or ________ , as the case may be, viewed through the edge • most commonly written with the ________ 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

21. d:\GOB.exe Go to GOB slide 3

22. Mutarotation • Mutarotation: the change in specific rotation that occurs when an a or b form of a carbohydrate is converted to an equilibrium mixture of the two

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

29. 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

30. Oxidation to Aldonic Acids • Oxidation of the -CHO group of an aldose to a -CO2H group can also be carried out using Tollens’, Benedict’s, or Fehling’s solutions

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

32. Fig 19.UNc, p.478

33. 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

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

35. Glucose Assay • the enzyme glucose oxidase is specific for b-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

36. Fig 19.UNa, p.480

37. Problem 19.40, p.491

38. Glycosides • _________ bond: the bond from the anomeric carbon of the glycoside to an -OR group • __________ 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 b-D-glucopyranoside • methyl a-D-ribofuranoside

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

40. Fig 19.UNa, p.475 Fig 19.UNb, p.476

41. d:\GOB.exe Go to GOB slide 5

42. The –OR group of the glycoside may be another monosaccharide – the resulting glycoside is then a disaccharide Examplesof important disaccharides follow:

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

44. beta-maltose

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

46. lactose

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