Kharkiv National Medical University Department of Medical and B ioorganic chemistry

1. KharkivNational Medical University Department of Medical and Bioorganic chemistry «Biological and Bioorganic Chemistry» Lecture№ 2 CLASSIFICATION, STRUCTURE AND CHEMICAL PROPERTIES OF CARBOHYDRATES Lecturer: As. Professor, Department of Medical and Bioorganic Chemistry,, Ph.D. LukianovaL.V.

2. Plan of lecture • 1. Carbohydrates, their functions and classification. • 2. Monosaccharides. Cyclic structures of monosaccharides. • 3. Mutarotation. • 4. Chemical properties of monosaccharides. • 5. Polysaccharides, their structure and application.

3. Carbohydrates are in composition of cells and tissues of all plant and animal organisms. They compose basic part of organic substance on the Earth.

4. Functions of carbohydrates 1. Carbohydrates act as a major chemical repository for solar energy. x CO2 + y H2O + solar energy → Cx(H2O)y + x O2 carbohydrate Energy is released and used for life activities : Cx(H2O)y + x O2 → x CO2 + y H2O + energy 2. Carbohydrates form structural material for cells in plants, bacteria, fungi and insects. 3. Carbohydrates act as structural elements of vitally important compounds (nucleic acids, coenzymes, vitamins).

5. Carbohydrate: a polyhydroxyaldehyde or polyhydroxyketone, or a substance that gives these compounds on hydrolysis

7. Aldoses n = 1-8 Ketoses n = 1-7 Monosaccharide • - a carbohydrate that cannot be hydrolyzed to a simpler carbohydrate; • - have the general formula CnH2nOn, where n varies from 3 to8 • aldose: a monosaccharide containing an aldehyde group • ketose: a monosaccharide containing a ketone group

8. Monosaccharides Most of them have sweet taste. About 20 monosaccharides occur naturally. They contain up to 10 carbon atoms. Monosaccharides are classified by their number of carbon atoms. Pentoses and hexoses are mostly wide spread in nature.

9. 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.

10. Aldehyde group Keto group Carbonyl group Ketopentoses Ketohexoses Aldopentoses Aldohexoses

11. Mannose Fructose Glucose Galactose Ribose 2-deoxyribose

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

13. Chiral center D- and L- Designations Sugars show optical isomerism.

14. 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

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

16. D,L Monosaccharides According to the conventions proposed byFischer: • 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 These two compounds serve as configurational standards for all monosaccharides!

17. One enantiomer rotates plane polarized light clockwise (designated (+))and another one – anticlockwise (designated (-)). (+)-glyceraldehyde is designated D-(+)-glyceraldehyde (-)- glyceraldehyde is designated L-(-)-glyceraldehyde

18. A monosaccharide whose highest numbered chiral center has the same configuration as D-(+)-glyceraldehyde is designated as D-sugar; one whose highest numbered chiral center has the same configuration as L-(-)-glyceraldehyde is designated as L-sugar. Nearly all naturally occurring sugars belong to D-series!

19. D-glucose D-galactose D-mannose D-glucose L-glucose enantiomers diastereomers If there are n chiral centers in a molecule, it will have 2n optical isomers. Therefore, glucose has 24 =16 optical isomers.

20. D,L Monosaccharides • Here are the two most common D-aldotetroses and the two most common D-aldopentoses:

21. D,L Monosaccharides • And the three common D-aldohexoses:

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

23. 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 hemiacetalformation; • anomers:carbohydrates that differ in configuration at their anomericcarbons.

24. 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.

25. Haworth Projections

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

27. hemiacetal hydroxyl group hemiacetal Cyclic structures of monosaccharides It has been found that monosaccbarides exist in the form of cyclic structures: Monosaccharides can undergo intramolecular reactions (within the molecule) to form hemiacetals which result in cyclic structures.

28. anomeric carbon atom Glycosidic OH-group anomers α-D-glucose D-glucose β-D-glucose Cyclic structure of glucoseAnomers

29. β–glucose α-glucose hemiacetal (glycosidic) hydroxyl α-D-glucopyranose Haworth projection formula α-D-glucose Fischer projection formula The structures of α-D-glucose and β-D-glucose may be drawn in a simple six membered ring form called pyranose structures. Pyran

30. α-D-ribofuranose β-D-ribofuranose Cyclic structure of ribose Furan

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

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

33. 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

34. 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:

35. Mutarotation

36. place of cycle opening α-D-glucopyranose (36%) α-D-glucofuranose D-glucose (open-chain form) 0.02% β-D-glucopyranose (64%) β-D-glucofuranose Ring-chain tautomerism

37. α-D-fructopyranose α-D-fructofuranose D-fructose β-D-fructofuranose β-D-fructopyranose Fructose

38. H+ D-glucopyranose 2,3,4,6,-tetra-O-methyl- D-glucopyranose Methyl-2,3,4,6,-tetra-O-methyl- D-glucopyranoside D-glucopyranose Chemical properties 1. Glycosides formation Methyl-D-glucopyranoside (mixture of α- and β –anomers) 2. Ethers formation

39. Glucose-1-phosphate 3. Esters formation.

40. glucitol glucose 4. Reduction mannitol mannose

41. 5. Oxidation a) Oxidation in alkaline medium (qualitative tests for aldoses and ketoses) • 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: mixture of products (complex) Fehling solution(blue) red-brown ppt Carbohydrates which give these reactions are called reducing.

42. Glucose Gluconic acid Glucose Glucaric acid b) Oxidation in neutral medium with mild oxidizing agents gives aldonicacids. c) Oxidation in acidic medium with strong oxidizing agents gives saccharic acids.

43. Acidity of polyhydric alcohols is higher than that of monohydric ones, due to negative inductive effect (-I) of hydroxyl groups. Hydrogen atoms of polyhydric alcohols are easily replaced by some heavy metals with formation of chelates: Chelates have bright coloration and their formation is used for the qualitative determination of polyhydric alcohols

44. D-mannose D-glucose Enediol D-fructose 6. Interconversions of aldoses and ketoses in weak alkaline medium

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

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

47. Oxidation by HIO4 • Periodic acid cleaves the C-C bond of a glycol:

48. Oxidation by HIO4 • it also cleaves -hydroxyaldehydes:

49. Oxidation by HIO4 • and -hydroxyketones:

50. 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: