Chemistry 121(01) Winter 2009

1. Introduction to Organic Chemistry and Biochemistry Instructor Dr. Upali Siriwardane (Ph.D. Ohio State) E-mail: upali@chem.latech.edu Office: 311 Carson Taylor Hall ; Phone: 318-257-4941; Office Hours: MTW 9:00 am - 11:00 am; TR 9::00 - !0:00 am & 1:00-2:00 pm. Chemistry 121(01) Winter 2009 December 19, Test 1 (Chapters 12-14) January 2 Test 1 (Chapters 15-16) February 6 (Chapters 17-19) February 27, (Chapters 20-22) March 2, 2009, Make Up Exam: Bring Scantron Sheet 882-E

2. Chapter 18:Carbohydrates Sections

3. Chapter 18: Carbohydrates 18.1 Biochemistry--An Overview18.2 Occurrence and Functions of Carbohydrates18.3 Classification of Carbohydrates18.4 Chirality: Handedness in Molecules18.5 Stereoisomerism: Enantiomers and Diastereomers18.6 Designating Handedness Using Fischer Projections18.7 Properties of Enantiomers18.8 Classification of Monosaccharides18.9 Biochemically Important Monosaccharides18.10 Cyclic Forms of Monosaccharides18.11 Haworth Projection Formulas18.12 Reactions of Monosaccharides18.13 Disaccharides18.14 General Characteristics of Polysaccharides18.15 Storage Polysaccharides18.16 Structural Polysaccharides18.17 Acidic Polysaccharides18.18 Glycolipids and Glycoproteins18.19 Dietary Considerations and Carbohydrates

4. Biochemistry Biochemistry is the study of the chemical processes in living organisms. It deals with the structure and function of cellular components, such as proteins, carbohydrates, lipids, nucleic acids, and other biomolecules. • Carbohydrates • Lipids • Proteins • Nucleic Acids • Use of carbohydrates as an energy source

5. Occurrence and Functions of Carbohydrates Occurrence Different objects such as sheets of paper, insect skeletons, fruits, cotton fabrics and ropes have one common feature: they all contain carbohydrates. Functions The chemical structure of carbohydrates, with their many hydroxyl groups and the ability to assume various spatial configurations, makes it possible for them to form nearly unlimited combinations with other carbohydrate molecules, as well as with proteins and lipids. The resulting structures perform important biological functions.

6. Classification of Carbohydrates Monosaccharides They consist of one sugar containing 3,4,5,6 and 7 carbon atoms and are usually colorless, water-soluble, crystalline solids. Some monosaccharides have a sweet taste. Examples of monosaccharides include glucose (dextrose), fructose (levulose), galactose, xylose and ribose.  Disaccharides a sugar (a carbohydrate) composed of two monosaccharides. Oligosaccharide An oligosaccharide is a saccharide polymer containing a small number (typically 3-10 monosaccharides Polysacharides Are relatively complex carbohydrates. They are polymers made up of many monosaccharides joined together by glycosidic bonds. They are insoluble in water, and have no sweet taste.

7. Chirality: Handedness in Molecules A "chiral" molecule is one that is not superimposable with its mirror image. Like left and right hands that have a thumb, fingers in the same order, but are mirror images and not the same, chiral molecules have the same things attached in the same order, but are mirror images and not the same.

8. Fischer Projection Formulas Fischer projection:a two dimensional representation for showing the configuration of a tetrahedral stereocenter • horizontal lines represent bonds projecting forward • vertical lines represent bonds projecting to the rear • the first and last carbons in the chain are written in full; others are indicated by the crossing of bonds

9. Stereoisomerism: Enantiomers and Diastereomers A Fischer projection is the most useful projection for discovering enantiomers. Compare the Glyceraldehydeenantiomer structures in this diagram. D- and L-Monosaccharides • 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. Properties of Enantiomers Enantiomers have, when present in a symmetric environment, identical chemical and physical propertiesexceptfor their ability to rotate plane-polarized light by equal amounts but in opposite directions. A mixture of equal parts of an optically active isomer and its enantiomer is termed racemic and has a net rotation of plane-polarized light of zero. Enantiomers of each other often do have different chemical properties related to other substances that are also enantiomers. Since many molecules in the bodies of living beings are enantiomers themselves, there is often a marked difference in the effects of two symmetrical enantiomers on living beings, including human beings.

11. What is Plane Polarized Light?

12. Optically active of enantiomers

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

14. D- and 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

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

16. D- and L-Monosaccharides • and the three common D-aldohexoses

17. D- and L-Monosaccharides Amino sugars • N-acetyl-D-glucosamine is a component of many polysaccharides, including connective tissue such as cartilage; it is also a component of chitin, the hard shell-like exoskeleton of lobsters, crabs, and shrimp

18. Classification of Monosaccharides Monosaccharideshave the general formula CnH2nOn the most common have from 3 to 9 carbons Triose (3) , tetrose(4), pentose(5), hexose(6) • aldose: a monosaccharide containing an aldehyde group:E.g. D-glucose • ketose: a monosaccharide containing a ketone group: E.g. D-Fructose

19. Carbohydrates: Monosaccharides Carbohydrate: a polyhydroxyaldehyde, a polyhydroxyketone, or a polymeric substance that gives these compounds on hydrolysis Monosaccharide:a carbohydrate that cannot be hydrolyzed to a simpler carbohydrate • monosaccharides have the general formula CnH2nOn • the most common have from 3 to 9 carbons • aldose: a monosaccharide containing an aldehyde group:E.g. D-glucose • ketose: a monosaccharide containing a ketone group: E.g. D-Fructose

20. Monosaccharides • monosaccharides are classified by their number of carbon atoms

21. Aldoses: Trioses, Tetroses and Pentoses

22. Aldoses: Hexoses

23. Ketoses: Hexoses

24. 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

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

26. Biochemically Important Monosaccharides

27. Cyclic Forms of Monosaccharides

28. Intramolecular cyclization • Simple sugars tend to exist primarily in cyclic form through hemiacetal or hemiketal formation. It is the most stable arrangement. CH2OH CH2OH H C C OH O O C C C C OH C C C C aldehyde hemiacetal

29. Intramolecular cyclization • The -OH group that forms can be above or below the ring resulting in two forms - anomers •  and  are used to identify the two forms. •  - OH group is down compared to CH2OH (trans). •  - OH group is up compared to CH2OH (cis).

30. CH OH 2 H O H H H OH O H C OH OH H C OH OH H HO C H H C OH CH OH 2 H C OH O OH H H CH OH H OH 2 OH H H OH Cyclization of D-glucose -D - glucose - D - glucose

31. Haworth Projection Formulas

32. Haworth Projections • the anomers of D-glucopyranose

33. Haworth Projections • 5- and 6-membered hemiacetals are represented as planar pentagons or hexagons viewed through the edge • most commonly written with the anomeric carbon on the right and the hemiacetal oxygen to the back right • - means that -OH on the anomeric carbon is cis to the terminal -CH2OH; - means it is trans • a 6-membered hemiacetal is shown by the infix -pyran- • a 5-membered hemiacetal is shown by the infix -furan-

34. Cyclic Structures Aldopentoses also form cyclic hemiacetals • the most prevalent forms of D-ribose and other pentoses in the biological world are furanoses • the prefix deoxy- means “without oxygen”

35. Cyclic Structures D-Fructose, a 2-ketohexose, also forms a cyclic hemiacetal

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

37. Conformational Formulas • the six-membered rings of pyranoses are more accurately represented as chair conformations

38. Conformational Formulas • compare the orientations of groups on carbons 1-5 in the Haworth and chair representations of -D-glucopyranose • in each case, beginning at carbon 1, they are up-down-up-down-up

39. 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

40. Mutarotation mutarotation of glucose

41. Fischer & Haworth Projection In solutions less than 1% of a sugar will be in the linear form shown as Fischer projection The normal form of most sugars is in a cyclic hemiacetal form shown as Haworth projection

42. Converting Fischer to Haworth Projection

43. a-Cyclic form of Gulose

44. Aldopentoses

46. Two monsaccharides connected by a bridging O atom called a glycosidic bond as in sucrose.

47. Reactions of Monosaccharides

48. Disaccharides

49. Polysaccharides

50. O H C H C OH HO C H H C OH H C OH CH OH 2 Polysaccharides • These are biopolymers composed of hundreds to thousands of simple sugar units (monosaccharides). • The most common monosaccharide used in polysaccharides is glucose.