Carbohydrate chemistry
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Carbohydrate chemistry

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Carbohydrate chemistry Carbohydrate chemistry Presentation Transcript

  • LETS LEARN SOME GREEK!!!! The name glucose comes from the Greek word glykys (γλυκύς), meaning "sweet", plus the suffix "-ose" which denotes a sugar 4 chiral centers give 24 = the 16 stereoisomer s of hexose sugars. Chirality, or "handedness", Greek, (χειρ), kheir: "hand” chiral carbons are enantiomers Alpha α and Beta β are letters in the Greek alphabet
  • σακχαρων Greek “sakcharon” = sugar
  • Carbohydrates • Carbohydrates, or saccharides (saccharo is Greek for ―sugar) are polyhydroxy aldehydes or ketones, or substances that yield such compounds on hydrolysis. • Carbohydrates include not only sugar, but also the starches that we find in foods, such as bread, pasta, and rice. • The term ―carbohydrate comes from the observation that when you heat sugars, you get carbon and water (hence, hydrate of carbon).
  • Carbohydrates and Biochemistry •Carbohydrates are compounds of tremendous biological importance: –they provide energy through oxidation –they supply carbon for the synthesis of cell components –they serve as a form of stored chemical energy –they form part of the structures of some cells and tissues •Carbohydrates, along with lipids, proteins, nucleic acids, and other compounds are known as biomolecules because they are closely associated with living organisms.
  • Glucose (a monosaccharide) Plants: photosynthesis chlorophyll 6 CO2 + 6 H2O C6H12O6 + 6 O2 sunlight (+)-glucose (+)-glucose starch or cellulose respiration C H O + 6 O2 energy 6 12 6 6 CO2 + 6 H2O +
  • Animals plant starch (+)-glucose (+)-glucose glycogen glycogen (+)-glucose (+)-glucose fats or aminoacids respiration (+)-glucose + 6 O2 energy 6 CO2 + 6 H2O +
  • CLASSIFICATION: 1- Monosaccharides (simple sugars): They can not be hydrolyzed into simpler units. E.g. glucose, galactose,ribose 2- Oligosaccharides (oligo = few): contain from two to ten monosaccharide units joined in glycosidic bonds. e.g.  disaccharides (2 units) e.g. maltose and sucrose,  trisaccharides (3 units).....etc. 3-Polysaccharides (poly = many): Also known as glycans. They are composed of more than ten monosaccharide units e.g. starch, glycogen, cellulose.....etc.
  • MONOSACCHARIDES CLASSIFICATION OF MONOSACCHARIDES 1- According to the number of carbon atoms: .Trioses, contain 3 carbon atoms.  Tetroses, contain 4 carbon atoms.  Pentoses, contain 5 carbon atoms.  Hexoses, contain 6 carbon atoms.  Heptoses, contain 7 carbon atoms.  Octoses. contain 8 carbon atoms.
  • 2- According to the characteristic carbonyl group (aldehyde or ketone group): - Aldo sugars: aldoses: Contain aldehyde group e.g. glucose, ribose, erythrose and glyceraldehydes. - Keto sugars: ketoses: Contain ketone group e.g. fructose, ribulose and dihydroxy acetone.
  • FORMS OF MONOSACCHARIDES:
  • TRIOSES: D- glyceraldehyde Dihydroxyacetone
  • TETROSES: Ketose CH2OH C = O H -C – OH CH2 OH D - erythrose D - erythrulose
  • PENTOSES:
  • HEXOSES:
  • HEPTOSES: IS A KETOSE SUGAR D - sedoheptulose
  • IT IS APTLY SAID THAT GLYCERALDEHYDE IS THE ‘REFERENCE CARBOHYDRATE’
  • Cyanohydrin Formation and Chain Extension. Kiliani-Fischer Synthesis- a series of reaction that extends carbon chain in a carbohydrate by one carbon and one chiral centre. 19
  • Determination of carbohydrate stereochemistry 1) HCN 2) H2, Pd/BaSO4 3) H2O CHO H OH H OH HNO3, heat CO2H H OH H OH CH2OH CO2H D-(-)-erythrose tartaric acid CHO H OH CH2OH Killiani-Fischer synthesis D-(+)-glyceraldehyde CHO HO H 1) HCN 2) H2, Pd/BaSO4 3) H2O H OH CH2OH HNO3, heat CO2H HO H H OH CO2H D-(-)-threose D-(-)-tartaric acid 20
  • 1) HCN CHO 2) H2, Pd/BaSO4 H OH 3) H2O H OH H CO2H HNO3, heat OH H OH H OH H OH CH2OH CO2H D-(-)-ribose ribonic acid CHO H OH H OH Killiani-Fischer synthesis CH2OH D-(-)-erythrose CHO HO H H 1) HCN 2) H2, Pd/BaSO4 3) H2O OH H OH CH2OH D-(-)-arabinose CO2H HNO3, heat HO H H OH H OH CO2H arabonic acid 21
  • 1) HCN 2) H2, Pd/BaSO4 3) H2O CHO H HO H OH H CO2H HNO3, heat OH H HO H CH2OH OH H OH CO2H D-(+)-xylose xylonic acid CHO HO H H OH Killiani-Fischer synthesis CH2OH D-(-)-threose CO2H CHO HO HO 1) HCN 2) H2, Pd/BaSO4 3) H2O H H H OH CH2OH D-(-)-lyxose HNO3, heat HO H HO H H OH CO2H lyxonic acid 22
  • CHO CHO CHO H OH HO H OH H OH HO H OH H OH H CH2OH H H CH2OH D-ribose CHO CHO CHO HO H OH H OH HO H OH H OH H OH H OH HO H OH H OH H OH H OH H CH2OH D-altrose CO2H OH CH2OH H HO H H OH H CH2OH D-mannose CO2H H OH HO H CH2OH OH HO OH H OH HO H HO H H OH H H OH H OH H OH H OH HO H OH H OH H OH H OH H H OH CO2H optically active HO H HO H H HO H H HO H HO H OH H OH H H OH CH2OH CO2H H enantiomers OH HO CO2H H optically active H CHO OH D-idose HO optically active CHO CH2OH OH CO2H H D-gulose CO2H CO2H D-lyxose CHO HO H optically active H OH HO optically inactive OH H OH CO2H H H D- glucose H HO HO H CO2H H H OH CH2OH CO2H H CHO OH D-allose H HO D-xylose H CH2OH H OH CH2OH D-arabinose CHO CHO D-galactose CH2OH D-talose CO2H H CO2H OH HO H OH HO H HO H H HO H HO H OH CO2H optically active H OH H CO2H optically inactive OH CO2H optically active 23
  • PHYSICAL PROPERTIES OF MONOSACCHARIDES Most monosaccharides have a sweet taste (fructose is sweetest; 73% sweeter than sucrose).  They are solids at room temperature.  They are extremely soluble in water:  Despite their high molecular weights, the presence of large numbers of OH groups make the monosaccharides much more water soluble than most molecules of similar MW.  Glucose can dissolve in minute amounts of water to make a syrup (1 g / 1 ml H2O). 
  • Sugar Relative Sweetness Lactose 0.16 Galactose 0.22 Type Disaccharide Monosaccharide  Maltose Xylose 0.32 0.40 Disaccharide Monosaccharide  Glucose 0.74 Monosaccharide   Sucrose 1.00 Invert sugar1.30  Fructose    1.73 Disaccharide Mixture of glucose and fructose Monosaccharide
  • ISOMERISM ENANTIOMER OPTICAL ISOMER ANOMER EPIMER ALDOSE-KETOSE ISOMER
  • THE STEREOCHEMISTRY OF CARBOHYDRATES Two Forms of Glyceraldehyde •Glyceraldehyde, the simplest carbohydrate, exists in two isomeric forms that are mirror images of each other:  10
  • Stereoisomers • These forms are stereoisomers of each other. • Glyceraldehyde is a chiral molecule — it cannot be superimposed on its mirror image. The two mirror-image forms of glyceraldehyde are enantiomers of each other.  Chirality and Handedness • Chiral molecules have the same relationship to each other that your left and right hands have when reflected in a mirror.  11
  • Chiral Carbons      Chiral objects cannot be superimposed on their mirror images —e.g., hands, gloves, and shoes. Achiral objects can be superimposed on the mirror images —e.g., drinking glasses, spheres, and cubes. Any carbon atom which is connected to four different groups will be chiral, and will have two nonsuperimposable mirror images; it is a chiral carbon or a center of chirality. –If any of the two groups on the carbon are the same, the carbon atom cannot be chiral. Many organic compounds, including carbohydrates, contain more than one chiral carbon.
  • n rule Van’t Hoff’s 2 When a molecule has more than one chiral carbon, each carbon can possibly be arranged in either the right-hand or left-hand form, thus if there are n n chiral carbons, there are 2 possible stereoisomers. Maximum number of possible stereoisomers = 2n Can you tell no. of possible stereoisomers of CHOLESTEROL?
  • D and L isomers (Enantiomers) Enantiomers : They are the mirror image of each others. CHO H - C– OH CH2OH D-Glyceraldehyde CHO HO-C-H CH2OH L-Glyceraldehyde
  • Carbohydrates are designated as D- or L- according to the stereochemistry of the highest numbered chiral carbon of the Fischer projection. If the hydroxyl group of the highest numbered chiral carbon is pointing to the right, the sugar is designated as D (Dextro: Latin for on the right side). If the hydroxyl group is pointing to the left, the sugar is designated as L (Levo: Latin for on the left side). Most naturally occurring carbohydrates are of the D-configuration. 1 CHO 2 H OH 3 HO H 4 H HO 6 CH2OH highest numbered "chiral" carbon 1 CHO H 2 OH 3 HO H 4 H OH 5 H OH 5 CH2OH D-Glucose highest numbered "chiral" carbon L-Arabinose CHO HO H highest numbered "chiral" carbon CHO H OH HO H HO H H OH HO H H OH CH2OH L- glucose highest numbered "chiral" carbon CH2OH 33 D-Arabinose
  • What’s So Great About Chiral Molecules? Molecules which are enantiomers of each • other have exactly the same physical properties (melting point, boiling point, index of refraction, etc.) but not their interaction with polarized light. •Polarized light vibrates only in one plane; • it results from passing lights through polarizing filter
  • Optical Activity A levorotatory(–) substance rotates polarized light to the left [e.g., l-glucose; (-)-glucose]. •A dextrorotatory(+) substance rotates polarized light to the right [e.g., d-glucose; (+)-glucose]. •Molecules which rotate the plane of polarized light are optically active. •Many biologically important molecules are chiral and optically active. Often, living systems contain only one of the possible stereochemical forms of a compound, or they are found in separate system. • –D-lactic acid is found in living muscles; D-lactic acid is present in sour milk. –In some cases, one form of a molecule is beneficial, and the enantiomer is a poison (e.g., thalidomide). –Humans can metabolize D-monosaccharides but not L-isomers; only L-amino acids are used in protein synthesis • • • • • •
  • The Aldotetroses. Glyceraldehyde is the simplest carbohydrate (C3, aldotriose, 2,3-dihydroxypropanal). The next carbohydrate are aldotetroses (C4, 2,3,4-trihydroxybutanal). aldotriose CHO H OH CH2OH D-glyceraldehyde CHO HO H CH2OH L-glyceraldehyde aldotetroses highest numbered "chiral" carbon 1 CHO 2 H OH 3 H OH 4 CH2OH D-erythrose 1 CHO HO 2 H HO 3 H 4 CH2OH L-erythrose CHO CHO highest numbered "chiral" carbon HO H H OH CH2OH D-threose highest numbered "chiral" carbon H HO OH H CH2OH L-threose highest numbered "chiral" carbon
  • Aldopentoses and Aldohexoses. Aldopentoses: C5, three chiral carbons, eight stereoisomers CHO OH OH HO H H OH H OH HO H OH H OH H H HO H H OH D-xylose D-arabinose OH CH2OH CH2OH CH2OH D-ribose HO H H H CH2OH CHO CHO CHO D-lyxose Aldohexoses: C6, four chiral carbons, sixteen stereoisomers CHO CHO CHO OH HO H OH H OH HO H OH H OH H OH H OH HO H OH H OH H OH H OH H D-allose CH2OH D-altrose H CHO H CH2OH H CHO OH HO H H OH HO H HO H H OH H CH2OH D- glucose CH2OH D-mannose H OH CH2OH D-gulose CHO CHO HO H H H CHO OH HO H OH HO H HO H H HO H HO H OH CH2OH D-idose H OH H OH CH2OH CH2OH D-galactose D-talose
  • Fischer Projections and the D-L Notation. Representation of a three-dimensional molecule as a flat structure. Tetrahedral carbon represented by two crossed lines: horizontal line is coming out of the plane of the page (toward you) vertical line is going back behind the plane of the paper (away from you) substituent carbon (+)-glyceraldehyde H C CH2OH HO CHO CHO CHO H OH H OH CH2OH CH2OH CHO CHO (-)-glyceraldehyde CHO HO C CH2OH H HO H CH2OH HO H CH2OH 39
  • Manipulation of Fischer Projections 1. Fischer projections can be rotate by 180° (in the plane of the page) only! CHO 180 ° H CH2OH OH HO H CH2OH CHO (R) (R) CHO 180 ° HO H CH2OH (S) CH2OH H OH CHO (S) 180° 180° Valid Fischer projection Valid Fischer projection 40
  • a 90° rotation inverts the stereochemistry and is illegal! 90 ° OH CHO H OH CH2OH (R) ° OHC CH2OH H (S) 90 ° 90° This is not the correct convention for Fischer projections Should be projecting toward you Should be projecting away you This is the correct convention for Fischer projections and is the enantiomer 41
  • 2. If one group of a Fischer projection is held steady, the other three groups can be rotated clockwise or counterclockwise. hold steady CHO H CHO OH HO CH2OH CH2OH H (R) (R) CHO H HO hold steady H OHC CH2OH CH2OH (S) Qu ickTime™ and a TIFF (Uncompressed) de co mpressor are need ed to see th is pi cture. 120° (S) Qu ickTi me™ and a TIFF (Uncompressed) d ecompresso r are nee ded to see th is pi ctu re. hold steady hold steady Qu ickTime™ and a TIFF (Uncompressed) de compressor are need ed to see thi s pi cture. 120° hold steady OH 120° Qu ickTime™ and a TIFF (Uncompressed) de compressor are need ed to see thi s pi cture. hold steady Qu ickTi me™ and a TIFF (Uncompressed) decompressor are nee ded to see this p icture. 120° hold steady Qu ickTime™ and a TIFF (Uncompressed) de co mpressor are need ed to see th is pi cture. hold steady 42
  • Cyclic Forms of Carbohydrates: Furanose Forms. O H+ + R1 H R2OH HO OR2 R1 H+, R2OH H R1 hemiacetal O OH (Ch. 17.8) H acetal OR OH H H R2O OR2 O cyclic hemiacetal H H+, ROH Ch. 25.13 O mixed acetal (glycoside) 43
  • In the case of carbohydrates, cyclization to the hemiacet creates a new chiral center. * CHO H H H OH OH CH2OH OH O H H OH H OH H * H H O H + H OH OH OH H * D-erythrose Converting Fischer Projections to Haworth formulas 44
  • 45
  • Cyclic Forms of Carbohydrates: Pyranose Forms. H 5 H CHO H H H H 4 1 2 HO OH 3 H H H OH H 4 OH H 5 H HO 5 4 OH H 1 H 3 OH OH OH new chiral center 1 2 3 HO H O H H 4 1 2 3 5 H O H HO H H OH CHO H OH OH OH H H 5 H OH H H 4 D-ribose OH HO HO O H H 1 2 3 OH OH HO O H H 4 1 2 3 H H H 5 OH OH ribopyranose 6 CH2OH OH H H 4 OH H HO 2 6 5 1 CHO H HO H HOH2C 6 2 3 HOH2C H OH H 4 OH HO 5 H D-glucose H 5 4 3 H OH H 2 OH 4 HO OH 1 H 3 H OH H 6 H OH 1 3 OH H O CH2OH O H H OH 5 OH new chiral center 1 CHO 6 CH 2OH OH 5 H 4 H OH HO 3 H 6 H H 1 H 2 OH O 4 HO CH2OH O H H OH 5 3 H H 1 2 OH OH glucopyranose 46
  • TWO TYPES OF PYRANOSE FORM Chair form Boat form 47
  • CHAIR FORM IS THERMODYNAMICALLY MORE STABLE Substituents on the ring carbons may be either axial (ax), projecting parallel to the vertical axis through the ring, or equatorial (eq), projecting roughly perpendicular to this axis. Two conformers such are these are not readily Interconvertible without breaking the ring. However, when the molecule is ―stretched‖ (by atomic force microscopy), an input of about 46 kJ of energy per mole of sugar can force the interconversion of chair forms. Generally, substituents in the equatorial positions are less sterically hindered by neighboring substituents, and conformers with bulky substituents in equatorial positions are favored.  Another conformation, the “boat” is seen only in derivatives with very bulky substituents.
  • Mutarotation and the Anomeric Effect. The hemiacetal or hemiketal carbon of the cyclic form of carbohydrates is the anomeric carbon. Carbohydrate isomers that differ only in the stereochemistry of the anomeric carbon are called anomers. Mutarotation: The - and -anomers are in equilibrium, and interconvert through the open form. The pure anomers can be isolated by crystallization. When the pure anomers are dissolved in water they undergo mutarotation, the process by which they return to an equilibrium mixture of the anomer. HOH2C HO HO H HO H H CHO OH H OH OH CH2OH D-glucose O HO H OH Trans HOH2C H O O -D-Glucopyranose (64%) ( -anomer: C1-OH and CH2OH are cis) H OH HO HO HO HO HOH2C HO HO Cis HOH2C OH HO HO O H HO OH -D-Glucopyranose (36%) ( -anomer: C1-OH and CH2OH are trans) 49
  • , α D-glucose (+110 ) D-glucose (+52.5 ) , D-glucose (+17.2 ) 50
  • Epimers: • Two monosaccharides differ only in the configuration around one specific carbon atom. • The D-glucose and D-mannose are epimers with respect to carbon atom 2, • D-glucose and D-galactose are epimers with respect to carbon atom 4.
  • Aldose-Ketose isomerism: Two monosaccharides have the same molecular formulae but differ in their functionl groups. • one has an aldehyde group (aldose e.g. glucose) • the other has a ketone group (Ketose e.g. fructose).
  • Monosaccharides of physiologic importance
  • 1-Pentoses: * -D-ribose is a structural element of ribonucleic acid (RNA)and coenzymes e.g. ATP, NAD, NADP and others. D-ribose-phosphate and Dribulose-5-phosphate are formed from glucose in the body (HMS). * 2-deoxy D-ribose enters in the structure of DNA. *D-lyxose: constituent of lyxoflavin in human myocardium.Lot of experiments are going to establish it as a potent myocardial infarction marker.
  • 2-Hexoses: 1- D-glucose (grape sugar, Dextrose as Dglucose is dextrorotatory ). • It is the sugar carried by the blood (normal plasma level 70-100 mg/dL) and the principal one used by the tissues. • It is found in fruit juices • obtained by hydrolysis of starch, cane sugar, maltose and lactose.
  • 2- D-Fructose (honey sugar = levulose as D-fructose is levorotatory). • It is found in fruit juices (fruit sugar ) • Obtained from sucrose by hydrolysis. • It is present in the semen in pyranose form 3- D-galactose: • It is a constituent of galactolipids and glycoprotein in cell membranes and extracellular matrix.
  • Important properties of monosaccharides
  • Iodocompounds Glucose when heated with conc. Hydroiodic acid loses all its oxygen and converted to Iodohexane. This suggests that glucose has no branched chain. Glucose conc.HI Iodohexane
  • Ester Formation   The – OH groups of monosaccharides can form esters with acids (phosphate & sulfate). Phosphate esters:    Glucose – 1 – phosphate Glucose – 6 – phosphate Sulfate esters:  Galactose – 3 – sulfate 61
  • Glucose – 6 - Phosphate 62
  • Sugar as reducing agent   The monosaccharides and most of the disaccharides are rather strong reducing agents, particularly at high pH. At alkaline pH aldehyde or keto group tautomerizes to form highly reactive ENEDIOL group. This group has strong reducing property. H C OH C R OH 1,2 enediol form 63
  • Trommer’s test-precursor of BENEDICT’S test CuSO4 + 2NaOH Cu(OH)2 + Na2SO4 (bluish white) 2Cu(OH)2 2 CuOH + H2O + O Cu2O + H2O (red) Trommer’s test is not convenient enough and later Benedict’s test replaced it. 64
  • Benedict’s Reagent (blue) Copper(I) oxide (red-orange ppt) Benedict’s reagent contains CuSO4,sodium carbonate and sodium citrate. Ammoniac silver nitrate solution may be reduced to metallic silver, producing a mirror-TOLLEN’s Test Alkaline Bismuth solution, known as Nylander’s solution, deposits black metallic bismuth on reduction. Picric acid in alkaline medium is reduced to picramic acid. Color changes from yellowish orange to mahogany red. In acid solution sugar reduces less vigorously.Barfoed’s test utilizes this fact for distinguishing monosaccharides 65
  • Reaction with strong alkalis  The sugar caramelises and produces a series of decomposition products,yellow and brown pigments develop,salts may form, many double bonds are formed between C-atoms. 66
  • Action of strong acid on monosaccharides    With conc. Mineral acids the monosaccharides get decomposed. Pentoses yield cyclic aldehyde ‘furfural’. Hexoses are decomposed to ‘hydroxymethyl furfural’ which decomposes further to produce laevulinic acid,CO,CO2 67
  • The furfural products can condense with certain organic phenols to form compounds having characteristic color. It forms the basis of certain tests used for detection of sugars. Molisch’s Test: With alpha-naphthol (in alcoholic solution)gives purple ring. A sensitive reaction but not specific. It is used as Group test of carbohydrate. Seliwanoff’s test:With resorcinol, a cherry red colour is produced. It is characteristic of D-fructose. Other tests are anthrone test, Bial-orcinol test 68
  • OSAZONE formation    Emil Fischer done this job to detect various sugars. Used to differentiate simple sugar by their varied form of osazone and rate of osazone formation. PREPARATION: they are obtained by adding a mixture of phenylhydrazine hydrochloride and sodium acetate to the sugar solution and heating in boiling water bath for 30 to 45 mins.The solution is allowed to cool slowly by itself.crystals are formed .A coverslip preparation is made on a clean slide and seen under microscope. 69
  •  70
  • Mullikin’s figures sugar  Glucose Fructose Sucrose Maltose  Lactose    Time(minutes) 4-5 2 30-45 after hydrolysis Osazone soluble in hot water Osazone soluble in hot water 71
  • Principle   Free carbonyl group of sugars react eith phenylhydrazine to form phenylhydrazone With excess phenylhydrazine, the adjacent C-atom of carbonyl group react with phenylhydrazine to form yellow compounds called osazone. 72
  •  73
  • 74
  • Oxidation of sugar 1. Aldonic acid: oxidation of an aldoses with Br2-water converts the aldehyde group to a carboxyllic group D-Glucose D-gluconic acid 2.Saccharic acid or aldaric acid: oxidation of aldoses with conc.HNO3 under proper conditions convert both aldehyde and primary alcohol group to –COOH group,forming dibasic sugar acids, the Saccharic acid or aldaric acid. D-Glucose D-Glucaric acid D-Galactose D-Mucic acid 75
  • 3. Uronic acid: When only the primary alcohol group of an aldose is oxidized to –COOH group, without oxidation of aldehyde group, a uronic acid is formed. D-Glucose D-Glucuronic acid D-galactose D-Galacturonic acid Due to presence of free –CHO group they exert reducing action. Biomedical importance 76
  • Reduction  Carbonyl groups can be reduced to alcohols (catalytic hydrogenation) H O R     H [H] H OH R Sweet but slowly absorbed Glucose is reduced to sorbitol (glucitol) Xylose can be reduced to xylitol Once reduced – less reactive; not absorbed
  •       Glceraldehyde & dihydroxyacetone to Glycerol. Ribose to Ribitol. Glucose to Sorbitol. Galactose to Dulcitol. Mannose to Mannitol. Fructose to Sorbitol & Mannitol 78
  •  Glycerol   Ribitol   Present in the structure of many lipids. Enters in the structure of Riboflavin. Myo-inositol    One of the isomers of inositol. A hydroxylated cyclohexane. Present in the structure of a phospholipid termed phosphatidyl inositol. 79
  • Interconversion of sugars  Glucose, Fructose and Mannose differ from each other only arrond C1- C3.So they are interconvertible in weak alkaline solution such as Ba(OH)2 or Ca(OH)2. This is due to same ENEDIOL formation during tautomerization. This is called Lobry de Bruyn-Van Ekenstein Reaction 80
  • H H HO O H C (R) OH H HO , H2O OH C OH HO H H HO , H2O HO HO O C (S) H H H OH H OH H OH H OH H OH H OH CH2OH CH2OH CH2OH D-mannose D-glucose HO , H2O CH2OH O HO H H OH H OH CH2OH D-fructose 81
  • Other sugar derivatives of biomedical importance       L-ascorbic acid Phytic acid Deoxy sugar Amino sugar Amino sugar acids Glycosides 82
  • L – Ascorbic acid O=C HO – C HO – C O H–C HO – C - H CH2OH Due to lack of enzymes it becomes a VITAMIN for human beings Glucuronic acid is reduced to L-Gulonic acid and then converted through L-Gulonolactone to L-Ascorbic acid in plants and most higher animals. 83
  • Phytic acid   The hexaphosphoric ester of inositol. Forms insoluble salts with Ca2+, Mg2+, Fe2+ & Cu2+   Prevent their absorption from diet in the small intestine. So it is better to avoid maize and legumes in diet of anaemic patient with iron rich diet or haematinic drugs. 84
  • Deoxysugars  Deoxyribofuranose   Present in DNA. L-Fucose   6-deoxy-L-galactose Important component of some cell membrane glycoproteins & blood group antigens. 85
  • 86
  • Aminosugars    Formed from the corresponding monosaccharide by replacing the –OH group at C2 with an amino (NH2) group. Are important constituents of GAGs & some types of glycolipids eg gangliosides. Are conjugated with acetic acid &/or sulfate to form different derivatives. 87
  • Aminosugars       Glucosamine Galactosamine Mannosamine Glucosamine – 2,6 – bisulfate (heparin) N-acetyl-glucosamine (hyaluronic acid) N-acetyl-galactosamine (chondroitin sulfate) 88
  • AMINO SUGAR Glycosylamine Anomeric –OH group is replaced by –NH2  e.g glucosylamine  Glycosamine -OH group attached to carbon atom other than the anomeric one.  e.g glucosamine  89
  • GLUCOSAMINE 90
  • AMINOSUGARS ACIDS Are formed of 6-C aminosugars linked to 3-C acid.  Examples:  Neuraminic acid: (Mannosamine + Pyruvic acid)  N-acetylneuraminic acid (Sialic acid)  Muramic acid (glucosamine + lactic acid)  91
  • Sialic Acid (NANA)   Enters in the structure of may glycolipids & glycoproteins. Forms an important structure of cell membrane & has many important functions:    It is important for cell recognition & interaction. It is an important constituent of cell membrane receptors. It plays an important role in cell membrane transport systems. 92
  • Neuraminic Acid 93
  • Glycosides    Formed by a reaction between the anomeric carbon (in the form of hemiacetal or hemiketal) with alcohols or phenols. Are named according to the reacting sugar. Any glycosidic linkage is named according to the type of parent sugar eg glucosidic, galactosidic or fructosidic linkages. 94
  • Types of Glycosides   Monosaccharide units may condense in the form of di-, oligo- & polysaccharides where the second sugar reacts as an alcohol & condenses with the anomeric carbon by removal of H2O. A sugar may also condense with a nonsugar radical (aglycon)  Nucleoside: (pentose sugar + nitrogenous base) 95
  • BIOMEDICALLY IMPORTANT GLYCOSIDES Cardiac glycosides: obtained from digitalis  They all contain steroids as aglycone.  Digitalis glycosides include digitoxin, gitoxin, gitalin and digoxin  Digoxin is class V antiarrhythmic drug according to Vaughan Williams classification.  Used in supraventricular arrhythmia especially heart failure with atrial fibrillation  99
  • Contraindicated in ventricular tachycardia.  Chemically, Digitonin 4Galactose +Xylose+digitogenin  (aglycone) OUABAIN: It gains interest as class 1C antiarrhythmic drug that inhibit active transport of sodium in myocardium in vivo. It prevents paroxysmal atrial fibrillation.
  • PHLORIDZIN:  Obtained from the root and bark of apple tree.  It blocks transport of sugar across mucosal cells of small intestine and renal tubular epithelium.  Displaces Na+ from the binding site of carrier protein and prevents the binding of sugar molecule and produces glycosuria. STREPTOMYCIN , the well known antibiotic is also a Glycoside.
  • BOOKS WHICH MADE SUGAR A LITTLE BITTER Text book of Biochemistry-Chatterjea ,Shinde  Text book of Biochemistry-Vasudevan  Text book of Biochemistry-Harper  Text book of Biochemistry-Orten & Neuhaus  Text book of Biochemistry-White  Text book of Biochemistry-N.V.Bhagavan  Text book of Biochemistry-Lehninger 