Chemistry of Monosaccharides - Final Marwa - PDF

CHEMISTRY OF CARBOHYDRATES  Outlines Carbohydrates o Definition o Classification Monocaccharides o Classifications o Isomerism o Derivatives DEFINITION Carbohydrates (CHO) are aldehyde or ketone derivatives of polyhydric alcohols or a...

CHEMISTRY OF CARBOHYDRATES  Outlines Carbohydrates o Definition o Classification Monocaccharides o Classifications o Isomerism o Derivatives DEFINITION Carbohydrates (CHO) are aldehyde or ketone derivatives of polyhydric alcohols or any substances derived from them.  CLASSIFICATION Carbohydrates are classified according to the hydrolytic products as follows:  Based on number of sugar units present: Monosaccharides: Cannot be hydrolyzed further into simpler forms. Disaccharides: Yield 2 molecules of same or different monosaccharide units on hydrolysis e.g. sucrose, lactose and maltose. Oligosaccharides: Yield 3-10 molecules of monosaccharide units on hydrolysis. Polysaccharides: Yield more than 10 molecules of same or different monosaccharide units on hydrolysis.  Homo-& Heteropolysaccharides. Monosaccharides  MONOSACCHARIDES 􀁺 Simplest group of carbohydrates, cannot be further hydrolysed. 􀁺 Categorization of monosaccharides is based on: the Functional Group. (Aldehyde or keto). the Number of Carbon atoms.  MONOSACCHARIDES No. of C-atoms carbonyl group Trioses Tetroses Pentoses Aldoses Ketoses Hexoses Heptoses Aldehyde CHO Ketone C O MONOSACCHARIDES BASED ON FUNCTIONAL GROUP  An aldose is a carbohydrate with aldehyde functionality. A ketose is a carbohydrate with ketone functionality. These monosaccharides contain three carbon atoms. The smallest aldose in human body is glyceraldehyde and the smallest ketose in human body is dihydroxyacetone. glyceraldehyde dihydroxyacetone PENTOSES  Hexoses: These monosaccharides contain 6 carbon atoms. The physiologically important hexoses are glucose, galactose, fructose and mannose. Glucose: It is the most important sugar of carbohydrates present in fruit juices and result from the hydrolysis of starch, cane sugar, maltose and lactose. Glucose is the sugar carried by the blood and is the principal sugar used by the tissues. It is the major source of energy ( Mainly for RBCs). It is present in urine in cases of diabetes mellitus due to raised blood glucose. Fructose: It is present in fruit juices and honey. Fructose can be changed to glucose in the liver and intestine, so it can be used in the body. Fructose serves as the major energy source of spermatozoa. It provides the fuel for sperm while they are in seminal fluid. Fructose accumulation occurs in hereditary fructose intolerance. (hypoglycaemia, enlarged liver (hepatomegaly), liver failure). Galactose: It is formed during hydrolysis of lactose (milk sugar). Galactose can be changed to glucose and metabolized. It is synthesized in the mammary gland to make the lactose of milk. It is a constituent of glycolipids and glycoproteins. Galactose accumulation occurs in galactosemia ( jaundice, Diarrhea, severe weight loss , Cataracts, liver damage and kidney problems).  Isomerism Isomers are different compounds that have the same molecular formula but different structural or stearic formula structural isomers, in which the atoms are joined in a different order, so that they have different structural formulae stereoisomerism, in which the order in which the atoms are joined is the same, but the molecules have a different spatial arrangement of the atoms and hence different three dimensional shapes.  STEREOISOMERS Isomers are compounds having the same structural formula but differ in spatial configuration. The formation of isomers is caused by the presence of asymmetric carbon atoms i.e. carbon atoms attached to 4 different atoms. The number of possible isomers of a compound depends on the number of asymmetric carbon atoms (n) and is equal to 2n. For example, glucose has 4 asymmetric carbon atoms, so the number of isomers = 16 isomers. All monosaccharides have asymmetric carbon atoms except dihydroxyacetone.  Asymmetric carbon atom – The carbon atom which is surrounded by four different atoms or groups is called asymmetric carbon atom. Types of isomers (1) D and L isomers: A special type of isomerism in the pairs of structures that are mirror images of each other (Enantiomers). This type of isomerism named according to the orientation of the -H and -OH groups around the carbon atom adjacent to the terminal primary alcohol carbon (C5 in glucose). When the -OH group is on the right, the sugar is a member of the D-series, when it is on the left, It is a member of the L-series. Most of naturally occuring are D sugars.  C3 H6 O3 Same Molecular formula CHO CHO H C OH HO C H CH2OH CH2OH D-glyceraldehyde L- glyceraldehyde  O H O H 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  Enantiomers non-superimposable mirror images (also called optical isomers) W W C C X Y Y X Z Z (2) Alpha and beta isomers (Anomers) These are isomers differing in the configuration of -OH and -H on C1 in the cyclic structure Pyranose and Furanose ring structure: The cyclic structure of glucose is favored and accounts for most of its chemical properties.  The stable ring structures of monosaccharides are similar to the ring structures of either pyran or furan. 99% of glucose in solution is in the pyranose form.  1 CHO H C OH 2 HO C H D-glucose 3 H C OH (linear form) 4 H C OH 5 CH2OH 6 6 CH2OH 6 CH2OH 5 O 5 O H H H OH H H 4 H 1 4 H 1 OH OH OH OH OH H 3 2 3 2 H OH H OH -D-glucose -D-glucose  6 CH2OH 6 CH2OH 5 O 5 O H H H OH H H 4 H 1 4 H 1 OH OH OH OH OH H 3 2 3 2 H OH H OH -D-glucose -D-glucose Cyclization of glucose produces a new asymmetric center at C1. The 2 stereoisomers are called anomers,  & . the OH at the anomeric C1:   (OH below the ring).   (OH above the ring).  1 CH2OH 2C O HO C H 1 CH2OH 3 HOH2C 6 O H C OH HO 4 5 H 2 H C OH H 4 3 OH 5 OH H 6 CH2OH D-fructose (linear) -D-fructofuranose (3) Epimers: These are isomers differing in the configuration of the -OH and -H on carbon atoms 2 or 3 or 4 of glucose. The most important epimers of glucose are mannose and galactose. Mannose is formed by epimerization at carbon 2 whereas, galactose by epimerization at carbon 4.  CARBON-2 EPIMERS H C O H C O H C OH HO C H HO C H HO C H H C OH H C OH H C OH H C OH CH2OH CH2OH D-GLUCOSE D-MANNOSE  CARBON-4 EPIMERS H C O H C O H C OH H C OH HO C H HO C H H C OH HO C H H C OH H C OH CH2OH CH2OH D-GLUCOSE D-GALACTOSE (4) Aldoses and Ketoses: Depending on the presence of aldehyde or keto group in the sugar. Fructose contains ketone group in position 2, whereas there is an aldehyde group in position 1 of glucose. (5) Geometrical isomers there are two forms of geometrical isomers : The cis-Isomer : In which the two identical atoms or groups are present in the same side of the two carbon atoms in the molecule. The Trans-Isomer : In which the two identical atoms or group are in two opposite sides of the two carbon atoms in the molecule. The carbonyl group - monosaccharides  All monosaccharides contain a free carbonyl group (aldo or keto). So all monosaccharides are reducing sugars. All monosaccharides reduce Benedict and fehling reagents.  Sugar derivatives Ester formation Sugar acids Sugar alcohols amino sugar amino sugar acids Deoxy sugars (Sugar derivatives) Esterification: Alcoholic groups of sugars react with acids to form esters. The most important biological esters are esters with phosphoric acid  Sugar acids 1. Produced by oxidation of carbonyl carbon to carboxylic group. 2. Or by oxidation of last hydroxy carbon to carboxylic group. 3. Or by oxidation of both. 1.Aldonic 2-Uronic  Importance of Glucuronic acid It is a highly polar molecule which is incorporated into proteoglycans.( Hyaluronic acid, Heparin). Conjugated with bilirubin to form soluble conjugated bilirubin. An inability to conjugate bilirubin, as in hepatic disease , is a cause of jaundice. Conjugated with certain drugs in liver to increase their solubility. Glucuronate-conjugated drugs are more easily cleared from the blood by excretion in urine. 3-Aldaric  Sugar alcohols The sugar is reduced to the corresponding alcohol: 1. Glyceraldehydes give glycerol 2. Dihydroxyacetone give glycerol 3. Ribose → ribitol 4. Glucose → sorbitol 5. Galactose → galactitol 6. Mannose → mannitol 7. Fructose → a mixture of equal amounts of sorbitol & mannitol  H α -D fructose β - D fructose Importance of sugar alcohols They are used widely in the food industry as sweeteners. They are commonly used in place of table sugar (sucrose). Sugar alcohols are not metabolized by oral bacteria, and so they do not contribute to tooth decay. Ribitol is a part of the structure of vitamin B2 (Riboflavin),  The glycerol backbone is found in all lipids known as triglycerides(TAG), the storage form of lipids in body. Glycerol is used in medical and personal care preparations for improving smoothness and providing lubrication (Glycerine). Glycerol can be used as a laxative. Glycerol can cause a rapid, temporary decrease in the internal pressure of the eye. This can be useful for the initial emergency treatment of severely elevated eye pressure  amino sugar CH2OH CH2OH H O H H O H H H OH H OH H OH OH OH O OH H NH2 H N C CH3 H -D-glucosamine -D-N-acetylglucosamine amino sugar - an amino group substitutes for a hydroxyl. An example is glucosamine. The amino group may be acetylated, as in N-acetylglucosamine.  amino sugar acid O H H3C C NH O COO R HC OH H H R= HC OH H OH CH2OH OH H NANA N-acetylneuraminate (sialic acid) N-acetylneuraminate (N-acetylneuraminic acid, also called sialic acid) is often found as a terminal residue of oligosaccharide chains of glycoproteins and glycosphingolipids. Sialic acid imparts negative charge to glycoproteins, because its carboxyl group tends to dissociate a proton at physiological pH. Importance of sialic acid: – Sialic acid is structural component in the terminal carbohydrate chains of mucoproteins. – sialic acid is increased in serum of tumour- bearing humans , it can be considered as tumor marker.  Deoxy sugars D 2.deoxy ribose Is derived from D.Ribose by de-oxygenation at carbon–2. It is found in DNA.  L-fucous Is derived from L-galactose by de-oxygenation at carbon–6. Importance of L-fucose L-fucose is usually CHO CHO located at the end HO C H HO C H of the carbohydrate H C OH Deoxygenation H C OH chains of H C OH at carbon-6 H C OH mucoproteins. HO C H HO C H CH2OH CH3 CH3 L-fucose levels are L-Galactose L-Fucose (LDDL) (6-deoxy-L-Galactose high in urine and blood of patients with diabetes mellitus, cancer and some other diseases. Which of the following monosaccharide has no assymetric carbon?  D-Glucose is based on position of (OH) to the right at a)Carbon (.1) b)Carbon(2) c) Carbon (3) d)Carbon(5) Glucose and galactose are epimers. This - means that: a) They are mirror images of each other, b) One is aldose and the other is ketose. c) They rotate plane polarized light in opposite directions. d) They differ only in configuration about one carbon atom. Carbohydrates are organic compounds made up of a. Carbon and hydrogen b. Carbon, hydrogen and oxygen c. Carbon, hydrogen, oxygen and nitrogen d. Carbon and oxygen  The minimum number of carbon in a monosaccharide is a.1 b. 2 c. 3 d. 4 All the following are monosaccharides except a-Glucose b-Fructose c-maltose d-galactose A carbohydrate found in DNA is a- Ribose B-Deoxyribose C-Ribulose D-All of these