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Carbohydrates (Introduction)
This document provides information about Ahmed Metwaly's academic positions and qualifications. It then discusses carbohydrates, including their definition, classification into mono-, oligo-, and polysaccharides, and the structures of common monosaccharides like glucose and fructose. The rest of the document covers carbohydrate chemistry, focusing on structural isomers of monosaccharides, cyclic forms, mutarotation, and reactions like those involving furfural.
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Carbohydrates (Introduction)
- 1. Associate Professor ofPharmacognosy , Faculty of Pharmacy, Al-Azhar University, Cairo, Egypt •Associate Professor, City of Scientific Research and Technological Applications (SRTA-City), Alexandria, Egypt •Senior research fellow, Liaoning University of Traditional Chinese Medicine, China (20118-2019) •Visiting scholar, School of Pharmacy, University of Mississippi, USA (2012-2014) Ahmed Metwaly
- 2. DEFINITION I (CH2O)n or H- C - OH I Carbo / hydrates Polyhydroxy aldehydes or ketones, or substances that upon hydrolysis yield polyhydroxy aldehydes or ketones.
- 3. - Desoxy sugars;rhamnose (C6H12O5), cymarose (C7H14O4) and digitoxose (C6H12O4), - Sugar alcohols e.g. sorbitol (C6H14O6), - Sugar acids e.g. gluconic acid (C6H12O7) - Amino sugars e.g. glucosamine (C6H13NO5).
- 4. Photosynthesis x CO2 +y H2O Chlorophyll Solar energy Cx (H2O)y + x O2 Metabolism C x (H2O) y + x O2 x CO 2 + y H2O + Energy
- 5. Carbohydrates Monosaccharides 1 Sugar unit. Oligosaccharides 2-10Sugar units. Polysaccharides > 10 sugar units.
- 6. Monosaccharides 1 Sugar unit. Cnumber Triose (3) Pentose (5) Hexose (6) Functional group. Aldehyde (Aldose) Ketones (Ketoses) Both
- 7. Oligosaccharides 2-10 Sugar units. Disaccharides. ReducingNon-Reducing Trisaccharides. Tetrasaccharides.
- 8. Polysaccharides > 10 sugarunits. Homosaccharides Glucans Fructosans Heterosaccharides Dissimilar monosaccharides Derived carbohydrates Polyuronides Mucopolysaccharides
- 9. sugars are white,crystalline in shape and with sharp melting points, while polysaccharides are white amorphous solids. Sugars have a sweet taste (to various degrees) polysaccharides are tasteless. monosaccharides are soluble in cold water and hot alcohol. Polysaccharides are partially soluble in hot water and insoluble in alcohol (cellulose is insoluble in all above mentioned solvents).
- 10. ▪Monosaccharides and watersoluble oligosaccharides are optically active.
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- 12. D & Ldesignations are based on the configuration about the single asymmetric C in glyceraldehyde. The lower representations are Fischer Projections. CHO C CH2OH HO H CHO C CH2OH H OH CHO C CH2OH HO H CHO C CH2OH H OH L-glyceraldehyde D-glyceraldehyde L-glyceraldehyde D-glyceraldehyde
- 13. ▪ ) CHO OH H OH H OH H OH H CH2OH CHO H HO OH H OH H OH H CH2OH CHO OH H H HO OH H OH H CH2OH CHO H HO H HO OH H OH H CH2OH CHO OH H OH H H HO OH H CH2OH CHO H HO OH H H HO OH H CH2OH CHO OH H H HO H HO OH H CH2OH CHO H HO H HO H HO OH H CH2OH Allose AltroseGlucose Mannose Gulose Idose Galactose Talose
- 14. - AND Howthe cyclic structure can be formed
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- 29. - AND -ANOMERS OF GLUCOSE: ➢When sugars undergo cyclization C-1 became a new chiral carbon and two isomers exist.They are called “ Anomers”. ➢In the -anomer the OH group is directed downside and in the -anomer is directed to the upper side. ➢These two forms have different specific rotation, in solution an equilibrium exist between the two forms (mutarotation phenomenon). O H HO H HO H OH OH H H OH O H HO H HO H H OH H OH OH O H OH OH H H OH H OH CH2OH H O H OH H OH H OH H OH CH2OH H Haworth formulations Chair forms, pyranose structure -D-glucopyranoside -D-glucopyranoside -D- glucopyranoside -D-glucopyranoside 1 6 1 1 5 5 anomeric proton
- 30. CHO OH H H HO OH H OH H CH2OH O H HO H HO H OH OH H H OH O H HO H HO H H OH H OH OH O H OH OH H H OH H OH CH2OH H O H OH H OH H OH H OH CH2OH H Formulae of D(+) Glucose Fisher projection formula Haworth formulations Chair forms 1 2 3 4 5 -glucopyranoside -glucopyranoside -glucopyranoside -glucopyranoside 1 6 1 6
- 31. The evidence ofcyclic configuration ▪ The existence of monosaccharides in ring rather than open chain structures and the size of the rings are verified by X-ray analysis and is supported by: 1. The existence of two anomers for the same sugar, e.g. - and -glucose as proved by the formation of two methyl glucosides. 2. The mutarotation phenomenon. 3. The difference in reactivity of glucose and other aldoses from true aldehydes (they do not give all the characteristic reactions of aldehydes e.g. Schiff’s reaction). - Aldoses and ketoses react with only one molecule of monohydric alcohol to give acetal unlike normal aldehydes and ketones that react with two molecules (one molecule to give the hemiacetal and another to transform the hemiacetal to acetal).
- 32. ▪Mutarotation: When asugar is dissolved in water, the specific rotation of the solution gradually changes until it reaches a constant value due to equilibrium between and - forms ( form is more positive value) ▪ Mutarotation is the change in the optical rotation because of The change in the equilibrium between two Anomers, when the corresponding Stereocenters interconvert. e.g. Freshly prepared solution of -glucose has a specific rotation +18.7o. When this solution is allowed to stand the rotation falls till reach + 52.7o.
- 33. Stereochemistry C C* O C* C* C* CH2OH H OH HO H HOH H OH H C C* O C* C* C* CH2OH HO H H OH HO H HO H H D-glucose L-glucose Enantiomers Epimers D-mannose D-galactose Diastereomers C C* O C* C* C* CH2OH H OH HO H HO H H OH H C C* O C* C* C* CH2OH HO H HO H H OH H OH H C C* O C* C* C* CH2OH H OH HO H H OH H OH H D-glucose D-mannose C C* O C* C* C* CH2OH HO H HO H H OH H OH H Two sugars that differ in configuration at only one chiral center Enantiomers Diastereomers Epimers Mirror images Pairs of isomers that have opposite configurations at one or more chiral centers but are NOT mirror images
- 34. ▪Anomers ???????????? ▪Structural isomers???????????????? ▪Cyclic isomers ????????????????
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- 36. Aldoses (e.g., glucose)have an aldehyde group at one end. Ketoses (e.g., fructose) have a keto group, usually at C2. C C OH H C H HO C OH H C OH H CH2OH D-glucose O H C H HO C OH H C OH H CH2OH CH2OH C O D-fructose
- 37. Glucose and fructosehave the same molecular formula C6H12O6. They have different structures with different functional groups (different connectivity). They are described as “structural isomers”. CHO CH CH CH CH CH2OH OH OH HO OH CH2OH C CH CH CH CH2OH OH OH HO D-Glucose D-Fructose O
- 38. O H OH C C H – C – OH HO – C – H HO – C – H H – C – OH H – C – OH HO – C – H H – C – OH HO – C – H CH2OH CH2OH D-glucose L-glucose For sugars with more than one chiral center, D or L refers to the asymmetric C farthest from the aldehyde or keto group. Most naturally occurring sugars are d isomers.
- 40. TERMS USED TODESCRIBE ISOMERISM: ▪ Glucose and galactose are different from each other in the stereochemistry of carbon 4. They are described as “4-epimers”. ▪ Glucose and mannose are different from each other in the stereochemistry of carbon 2. They are described as “epimers”(also diastereoisomers) CHO CH CH CH CH CH2OH OH OH HO HO D- Mannose Epimers: CHO CH CH CH CH CH2OH OH OH HO OH D-Glucose CHO CH CH CH CH CH2OH OH HO OH D-Galactose HO CHO CH CH CH CH CH2OH OH OH HO OH D-Glucose
- 41. CHO CH CH CH CH CH2OH OH HO OH D-Galactose HO CHO CH CH CH CH CH2OH OH OH HO HO D- Mannose CHO CH CH HC CH CH2OH OH HO OH D-Glucose OH ➢Galactose andMannose are different from each other in the stereochemistry of carbons 2 and 4. They are described as “Diastereoisomers”. They are not mirror images and differ widely in both physical and chemical properties.(2,4) ➢“Epimers” are diastereoisomers which differ in configuration of single asymmetric center adjacent to anomeric one (C=O) Typical epimers 2,4-diasteriomers
- 42. CHO CH2OH CHO CH2OH CHO CH2OH CHO CH2OH D-glucose L-glucose D-alloseD-mannose CHO CH2OH CHO CH2OH CHO CH2OH CHO CH2OH D-glucose D-mannose D-glucose D-galactose enantiomers Diastereoisomers epimers 4-epimers
- 43. An aldehyde canreact with an alcohol to form a hemiacetal. A ketone can react with an alcohol to form a hemiketal. O C H R OH O C R R' OH C R R' O aldehyde alcohol hemiacetal ketone alcohol hemiketal C H R O R' R' OH "R OH "R + +
- 44. Pentoses and hexosescan cyclize as the ketone or aldehyde reacts with a distal OH. Glucose forms an intra-molecular hemiacetal, as the C-1 aldehyde & C-5 or react to form a 6-member pyranose ring, named after pyran. These representations of the cyclic sugars are called Haworth projections. H O OH H OH H OH CH2OH H OH H H O OH H OH H OH CH2OH H H OH -D-glucose -D-glucose 2 3 4 5 6 1 1 6 5 4 3 2 H CHO C OH C H HO C OH H C OH H CH2OH 1 5 2 3 4 6 D-glucose (linear form)
- 45. ▪ Any carbohydrate+ Alcoholic -naphthol then add conc. H2SO4 on the wall of the test tube Violet ring between the two layers. Treatment with conc. mineral acid (HCl or H2SO4) leads to dehydration of sugars and formation of the corresponding furfural. O CHO O CHO HOH2C Pentoses Hexoses Furfural (volatile) 5-Hydroxymethyl furfural (less volatile) Dehydration Dehydration
- 47. ▪ Reaction offurfural with amines resulted in Schiff’s bases with different colors used as color tests. ▪ (Differentiate between Pentoses and Hexoses): ▪ Pentose + conc. acid and heat, expose the vapours to Aniline acetate paper Red colour ▪ Hexoses give negative result. (for keto-hexoses): Sugar solution + few crystals of Resorcinol + Equal volume of conc. HCl and warm on water bath Rose Red Colour.
- 48. ▪ Sugar (H2O)+phenyl hydrazine hcl+ naac, heat (50 min), cool examine ozazone crystals under the microscope. The ozazone are yellow, crystalline with sharp m.P. Glucose, mannose fructose will give the same crystals (reaction involves C-1 and C-2) due to destruction of asymmetric center at C-2. CHO CHOH 3 PhNH-NH2 CH=N-NH-Ph CH=N-NH-Ph Ozazone crystals + Ph-NH2 + NH3 (characteristic) sugar phenyl hydrazine HCl
- 49. O HO OH OH CH2OH HO C6H5NHNH2 via open-chainform D-glucose C OH H HO OH H OH H CH2OH CH OH H H HO OH H OH H CH2OH CH C H HO OH H OH H CH2OH NNHC6H5 CHNHNHC6H5 C O H HO OH H OH H CH2OH CH2NHNHC6H5 C6H5NHNH2 C NNHC6H5 H HO OH H OH H CH2OH CH2NHNHC6H5 C N H HO OH H OH H CH2OH CH NH NHC6H5 NHC6H5 H NH NNHC6H5 C6H5NHNH2 -NH3 -C6H5NH2 CH C H HO OH H OH H CH2OH NNHC6H5 NNHC6H5 D-Mannose phenylosazone or D-glucoe phenylosazone
- 50. CH C H HO OH H OH H CH2OH NNHC6H5 NNHC6H5 D-Mannose phenylosazone or D-glucoephenylosazone N N H N R NHC6H5 C6H5 Where R = HO H H OH CH2OH H OH · Notice that the asymmetry at C-2 is lost, so that D-glucose, D-mannose, and D-fructose all form the same osazone. ·The reaction does not continue further down the chain to C-3 by a similar series of steps possibly because of stabilization of the osazone due to hydrogen-bonding
- 52. n COOH CH2OH (H OH) CHO CH2OH (H OH)nMild Oxidation Br2 CHO CH2OH (H OH)n HNO3 Strong Oxidation n COOH COOH (H OH) Glucaric acid (Acyclic St.) Protection Oxidation CHO CH2OH (H OH)n Glucuronic acid (cyclic St.) n CHO COOH (H OH) Gluconic acid (Acyclic St.)
- 53. ▪ These areoxidizing agents like Bromine water (or I2) that convert the CHO group to COOH to produce “onic acids”. ▪ N.B. Ca gluconate (I.V. or orally) is used in case of calcium therapy, Ferrous gluconate (I.V. or orally) is used in iron deficiency. CHO CH CH CH CH CH2OH OH OH HO OH D-Glucose COOH CH CH CH CH CH2OH OH OH HO OH Gluconic acid I2 or Fehling's
- 54. ▪ These areoxidizing agents like HNO3 that convert the CHO and CH2OH group to COOH to produce “aric acids”. CHO CH CH CH CH CH2OH OH OH HO OH D-Glucose COOH CH CH CH CH COOH OH OH HO OH Saccharic acid HNO3
- 55. ▪Glalactaric acid (Mucicacid) test: ▪Oxidation of galactose resulted in the formation of Galactaric acid. It is a meso compound insoluble in water and have zero optical rotation. CHO CH CH CH CH CH2OH OH HO OH D-Galactose COOH CH CH CH CH COOH OH HO OH Galactaric acid HNO3 HO HO
- 56. ▪ It iscarried out by first protecting the – CHO group, followed by oxidation of the - CH2OH group, or in one step by using enzyme to give aldouronic acid, e.g. oxidation of glucose into glucuronic acid. CHO CH CH CH CH CH2OH OH OH HO OH D-Glucose CHO CH CH CH CH COOH OH OH HO OH Glucuronic acid O COOH H H OHOH H H OH OH H
- 57. ▪ This resultedin the reduction of the CHO to CH2OH producing “sugar alcohols”. Sodium borohydride or H2/pt are examples of reducing agents. ▪ E.G. Glucose reduced to sorbitol which act as mild laxative while mannose reduced to mannitol which is used as osmotic diuretic, vasodilator and in lab. Diagnosis of kidney function. CHO CH CH CH CH CH2OH OH OH HO OH D-Glucose CH2OH CH CH CH CH CH2OH OH OH HO OH Sorbitol H2/Pt
- 58. 58 CH O HO H HOH H OH H OH CH2OH D-mannose CH2OH HO H HO H H OH H OH CH2OH NaBH4 H2O D-mannitol "does not promote tooth decay" "not non-caloric"