Chemistry of carbohydrates and isomerism

carbohydrates with their brief introduction and their classification. then structural features of carbohydrates

1. CHEMISTRY OF CARBOHYDRATES

2. CARBOHYDRATES Aldehyde or Ketone derivatives of polyhydroxy alcohols. General formula (CH 2 O)n

3. BIO MEDICAL IMPORTANCE Most abundant bio molecules. Main source of energy (4 kcal/gm ) . A bsolutely required for RBCs’ & brain cells. Storage form of energy i.e. starch & glycogen. Required for oxidation of fats. Excess CHO are converted into fats. Glyco protein & Glyco lipids are components of cell membrane. Structural basis of many organisms. Used as drugs i.e. antibiotics & cardiac Glycosides. .

4. CLASSIFICATION Monosaccharides Disaccharides Oligosaccharides Polysaccharides Derived carbohydrates

5. MONOSACCHARIDES Simplest sugars, cant be hydrolyzed into simpler molecules. Further classified as, Aldoses Ketoses

6. NAME GENERAL FORMULA ALDOSES KETOSES TRIOSES C 3 H 6 O 3 GLYCER- - ALDEHYDE DIHYDROXY- -ACETONE TETROSES C 4 H 8 O 4 ERYTHROSE ERYTHROLUSE PENTOSES C 5 H 10 O 5 RIBOSE RIBULOSE HEXOSES C 6 H 12 O 6 GLUCOSE FRUCTOSE HEPTOSES C 7 H 14 O 7 SEDOHEPTOLUSE NONOSES C 9 H 18 O 9 NEURAMINIC- -ACID

7. DISACCHARIDES Condensation products of 2 monosaccharide units. MALTOSE (D Glucose + D Glucose) SUCROSE (D Glucose + D Fructose) LACTOSE (D Glucose + D Galactose)

8. OLIGO SACCHARIDES Condensation products of 3-10 mono saccharide units,most of them are not digested by human enzymes. α DEXTRINS MALTO TRIOSE

9. POLY SACCHARIDES Condensation products of > 10 mono saccharide units. HOMO POLY SACCHARIDES HETRO POLY SACCHARIDES

10. HOMO POLYSACCHARIDES Have only one type of mono saccharide units. STARCH GLYCOGEN CELLULOSE INULIN DEXTRIN DEXTRAN CHITIN

11. HETRO POLYSACCHARIDES MUCO POLY SACCHARIDES Also known as Glycosaminoglycan. Hyaluronic Acid,Chondriotin sulfate, Heparin sulfate, Keratin sulfate, Dermatin sulfate, Blood group substances. GLYCO CONGUGATES Proteo glycans Glyco lipids Glyco proteins

12. DERIVED CARBOHYDRATES . Reduction products i.e. Polyols (glycerol) Oxidation products i.e. sugar acids Deoxy sugars i.e. DNA

13. MONOSACCHARIDES TRIOSES Glyceraldehyde & Dihydroxy acetone. Intermediates of glycolysis. Precursor of Glycerol TETROSES Erythrose-4-PO 4 Intermediate of HMP shunt.

14. DEOXY SUGARS L- Fucose Deoxy Glucose D- Ribose L- Arabinose D- xylose

15. HEXOSES Glucose Fructose Galactose Mannose

16. MONOSACCHARIDES

17. PHYSICAL PROPERTIES Colorless, crystalline solids , sweet taste, water soluble compounds. Aldoses Ketoses Poly Hydroxy alcohols i.e. having (OH - ) groups Depending upon the no. of (OH - ) groups, they contain one or more centre of Asymmetry, which affects their optical & biological activity.

18. Dihydroxy acetone (ketotriose) is an exception, (does not have any asymmetric carbon). Glyceraldehyde (aldotriose) is called as the “REFERENCE SUGAR”. Carbonyl carbon Asymmetric carbon

19. STRUCTURAL ASPECTS ISOMERISM IN MONOSACCHARIDES Stereo isomerism Enantiomers D & L isomers Optical isomers Aldose-Ketose isomers Anomers Epimers Pyranose & Furanose isomers

20. STEROISOMERISM 2 or more Monosaccharides having same formula, but differing from each other in structural configuration i.e. spatial arrangement of H or OH atoms in their structure.

21. ASYMMETRICAL(CHIRAL) CARBON 4 different groups attached to the same carbon . Parent compound (reference molecule) is Glyceraldehyde (1 asymmetric C).

22. In general a molecule with n chiral center can have 2 n stereo isomers. Glyceraldehyde 2 1 Glucose 2 4

23. ENANTIOMERS

24. The configuration of H & OH groups at the second Carbon atom of Glyceraldehyde forms D & L sugars. Penultimate carbon atom is the reference carbon for naming D & L mirror images.

25. Non super imposable complete mirror images, differ in configuration at every chiral center. In D form OH group is on the RIGHT , while in L form OH group is on the LEFT of the chiral carbon. D & L isomers differ from each other by orientation around PENULTIMATE CARBON (C -5 in case of Glucose molecule) ,farthest from the carbonyl(C= O)carbon. Human body can metabolize D-sugars only. Naturally occuring sugars are D-sug ars except L-Arabinose .

26. OPTICAL ISOMERISM Presence of asymmetric C atom confers optical activity to the carbohydrates. When a beam of plane polarized light is passed through a carbohydrate solution It will rotate the light either to right DEXTRO ROTATORY(+) to left LEVO ROTATORY (-)

27. OPTICAL ISOMERISM The direction of rotation of plane polarized light is independent of the stereo-chemistry of sugar. Sugar may be designated as, D(-) ,D(+) or L(-) ,L(+) Naturally occuring form of Fructose is D but it is levo rotatory. i.e. ( D-) Glucose is D sugar, but dextro rotatory i.e. (D+)

28. Plane polarized light does not rotate to right or left, if Compound does not possess plane of asymmetry. Equal amounts of dextro or levo isomers are present RECEMIC MIXTURE. Meso compounds having asymmetric carbon but due to internal compensation i.e . Meso tartaric acid.

29. EPIMERS Sugars that differ only in the configuration around one Carbon atom (other than reference carbon).

30. ALDOSE-KETOSE ISOMERS

31. CYCLIC STUCTURE OF MONO SACCHARIDES

32. Cyclic structures are formed by the reaction between an ALDEHYDE/KETONE group and a HYDROXYL group in a monosaccharide with 5 or more carbon atoms. Cyclic structure is thermodynamically favored and accounts for many properties of mono -saccharides

33. The open chain form ( FISCHER PROJECTION ) is found in < 0.1% of the molecules in an aqueous solution. An intra molecular reaction in which one of the OH group of the sugar is added to the Aldehyde/ Ketone group of the same molecule ---- forms a cyclic structure. The cyclic (ring) structure is called ----------- HAWORTH PROJECTION. The carbonyl carbon(C-1 of Aldose /C-2 OF KETOSE) in ring structure is called ANOMERIC CARBON

34. HEMI ACETAL LINKAGE

35. HEMIKETAL LINKAGE

36. HEMI KETAL LINKAGE Condensation between Ketone group and a OH group forms the hemi Ketal linkage. Condensation between the Aldehyde/Keto group is in 1:1. As a result of these linkages ANOMERIC CARBON gives an additional asymmetric carbon. Depending upon the configuration, OH group are found above or below the ring. OH group on the right in Fischer projection appear under the ring in Haworth projection ,while those on the left are above the ring.

37. OH group at C-5 / C-6 reacts with the Keto group at C-2, forming a FURANOSE/PYRANOSE cyclic structure having a hemi Ketal linkage. D-Fructose readily forms the Furanose ring. Common anomer of Fructose is the β - D Fructose.

38. In Aldohexoses the OH group at C-5 reacts with the c=o group and forms a six member ring--- PYRAN RING . Sugars having this ring are called PYRANOSES . If the OH group at C-4 reacts, a five member ring--- FURAN RING is formed & Sugars are called FURANOSES . OH group to the right is below the plane---- α Oh group to the left is above the plane of symmetry-- - β

39. ANOMERS Anomeric carbon by giving an additional chiral carbon makes the total isomers 2 5. (32) Anomeric carbon gives 2 stereo isomers i.e. α & β ANOMERS . α & β forms are not Enantiomers. They differ only in respect to configuration around Anomeric carbon. They are present only in cyclic form, & do not show the Aldehyde group normally present in Glucose. Ring structure is also called AMYLENE OXIDE .

40. MUTA ROTATION In Glucose solution ,2/3 of sugar exist as β form,& 1/3 as α form. Inter conversion of α & β forms is called MUTA ROTATION . In the solution there is opening of Hemiacetal ring to form traces of Aldehyde sugar & then Re condensation to the cyclic form.

41. When plane polarized light is passed through a Molar solution of D- Glucose, Its specific rotation keeps on changing α - D Glucose in the solution shows --+112 ˳ while β -Glucose shows ---- +19 ˳ . After a certain period of time two forms reach at an end point---- +19 ˳ . Mutarotation leads to an equilibrium between α & β forms in which 62% of the molecules are present in the β form , while 38% in the α form. a

42. CLINICAL SIGNIFICANCE α & β Anomers can be obtained in pure forms. It is possible to determine the sugar content of different beverages.

43. PYRANOSE/FURANOSE ISOMERS

44. BOAT & CHAIR ISOMERS

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