Carbohydrate Chemistry Lecture Notes PDF

Carbohydrate Chemistry by Faculty of medicine Menoufia university Department of medical biochemistry and molecular biology  A) Knowledge and Intended Understanding learning  By the end of the course, students shoul...

Carbohydrate Chemistry by Faculty of medicine Menoufia university Department of medical biochemistry and molecular biology  A) Knowledge and Intended Understanding learning  By the end of the course, students should be able to: outcomes  Define the importance and (ILOs) types of carbohydrates  Illustrate the classification of monosaccharides  Enumerate the monosaccharide derivatives and describe their structure and functions.  Carbohydrats  Carbohydrates (CHO) are aldehyde or ketone derivatives of polyhydric alcohols or any substances derived from them.  Importance of Carbohydrates Exam  Glucose is the major fuel of the mammalian tissue.  Oligo- and polysaccharides are important constituents of cell membranes.  Cellulose forms the cell walls of plants and is important in diet, preventing constipation. As it stimulates peristalsis  Mucopolysaccharides are important components of connective tissues. Mucopolysaccharides include :  Heparin is the most important natural anticoagulant.  Carbohydrates may combine with lipids forming glycolipides or protein forming glycoproteins  Classification of Carbohydrates Carbohydrates are classified according to the hydrolytic products as follows: (A) Monosaccharides: Product of undergoing hydrolysis  They cannot give simpler forms on hydrolysis.  They are composed of one sugar unit (B) Disaccharides:  They are composed of 2 sugar units; sucrose, lactose and maltose. (C) Oligosaccharides:  These are carbohydrates which are composed of or give 3- 10 monosaccharide units on hydrolysis. (D) Polysacchandes:  These are carbohydrates which are composed or give more than 10 monosaccharide units on hydrolysis; starch and dextrins.  MONOSACCHARIDES  Monosaccharides have the general formula Cn(H2O)n.  There are many classifications of monosaccharides:  The presence of aldehyde or ketone groups into: Glycerose =  Aldoses e.g: glycerose, erythrose, ribose & glucose glyceraldehyde  ketoses e.g: dihydroxyacetone, erythrulose, ribulose & fructose.  The number of carbon atoms as: (1) Trioses:  They contain three carbon atoms. (2) Tetroses:  These contain four carbon atoms. (3) Pentoses:  These contain five carbon atoms.  They are important constituents of nucleotides, nucleic acids and many enzymes. Aldo-triose Keto-triose The suffix (ulose) = ketone Aldo-tetrose Keto-tetrose (4) 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  It results from the hydrolysis of starch, cane sugar, maltose and lactose.  It is converted to all carbohydrates in the body e.g galactose, ribose and glycogen.  Glucose is the sugar carried by the blood and is the principal sugar used by the tissues.  It is the major source of energy.  It is present in urine in cases of diabetes mellitus due to raised blood glucose.  Fructose  It is present in fruit juices and honey.  It results from the hydrolysis of cane sugar and of inulin. Cane sugar = sucrose  Fructose can be changed to glucose in the liver and intestine, so it can be used in the body.  Fructose accumulation occurs in hereditary fructose intolerance.  It is the sugar of semen.  Galactose  It is formed during hydrolysis of lactose (milk sugar).  It can be metabolized to glucose.  It is formed in the mammary gland to make the lactose of milk.  It is a constituent of glycolipids and glycoproteins.  Galactosemia and cataract result from error in its metabolism. Galactose will be found in blood Inability of breaking down galactose Mannose  It is formed during the hydrolysis of gums.  It is a constituent of many glycoproteins. N.B : The straight open chain formula of sugars fails to explain some reactions e.g aldo sugars do not give all reactions of aldhydes, this mean that aldhyde group is masked in solutions. The aldhyde group of aldosugar undergo the following: Hydration of aldhyde group of sugar to form aldenol group This is followed by subsequent condensation between one of the –OH aldenol group and OH group of C4 or C5 to form ring structure( hemiacetal structure). if the remaining OH is on right , it is called α sugar, while it is called β sugar if it is on the left side PHYSICAL PROPERTIES OF MONOSACCHARIDES A-Monosaccharides are colorless, crystalline and sweet substances. B-Sugars exhibit various forms of isomerism.  Definition: 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 Or What is asymmetric carbon atom? groups It is the carbon atoms which 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.  Exam (enumerate) Types of isomerism : (1) D and L isomers (2) Pyranose and Furanose ring structure (3) Alpha and beta anomers (4) Epimers (5) Aldoses and Ketoses All isomers are stereo isomers except D and L isomers  This type of isomerism depends upon the orientation of the -H and -OH groups around the subterminal carbon atom.  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 the monosaccharides occurring in mammals are of the D-configuration. O H Mirror images of each other 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 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.  - D-Glucopyranose -D- Glucofuranose  Alpha and beta anomers  These are isomers differing in the configuration of -OH and -H on C1. Anomeric carbon N.B: the arrangement of H and OH around the carbon atoms is as follows ; Alpha :-OH on right side in old ring chain is written downwards. Beta :-OH on left side in old ring chain is written upwards. Aldoses and ketoses  Definition: - These are isomers depending on the presence of aldhyde or ketone group.  Example: - Glucose and fructose.  Epimers  These are isomers differing in the configuration of the -OH and -H on carbon atoms 2, 3 and 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. Exam C-Optical activity:-  Definition:- it is the ability of a compound to rotate the plane polarized light either to the right (+)dextrorotatory or to the left(-) levorotatory.  Plane polarized light (PPL): - is a light obtained by passing a beam of ordinary light through Nikol’s prism (CaCo3). Exam  Specific rotation: -  It is the angle of rotation specific for each optically active substance.  Example: - Specific rotation of glucose is (+52,5).  Note :- Glucose is dextrorotatory so it is called dextrose while fructose is levorotatory so it is called levulose.  Racemic (or DL) mixture:- (EXAM)  It is a mixture containing equal amounts of dextrorotatory and levorotatory isomers, the resulting solution has no optical activity since the activities of each isomer cancel one another.  Notes :-  All monosaccharides are optically active because they contain asymmetric carbon atoms except except dihydroxyacetone.  Change Mutarotation :- Exam Definition: - It is the gradual change in the specific rotation of an optically active compound when a freshly prepared solution is left to stand.  -glucose (fresh) gives specific rotation of +110  β-glucose (fresh) gives specific rotation of +19.5  When both anomers are left to stand, they change slowly into an equilibrium mixture which has a specific rotation of +52.5.  Explanation: - It is due to opening of the hemiacetal ring formed by combination of an aldhyde and alcohol groups and reformation with change in position of -H and -OH groups on carbon 1 till equilibrium. Anomeric carbon Derivatives of monosaccharides Exam 1.Deoxy sugars :- (enumerate) Definition:- These are sugars in which the hydroxyl group is replaced by a hydrogen atom. Example:- Deoxy ribose from ribose :- used in DNA L-fucose (6-deoxy galactose) :- used in glycoproteins D-galactose Septa-deoxy-L-galactose = 2.Amino sugars (hexosamines):- Definition:- These are sugar in which the OH group of the second carbon is replaced by an amino group (NH2). Examples:- Glucosamine:- Enter is structure of hyaluronic acid Galactosamine:- Chondrotin sulfate Mannosamine :- Erythromycin. Found in some antibiotics 3.Amino sugar acids:- Definition:- these are amino sugars with addition of an acid (either pyruvic or lactic acid). Examples:-Neuraminic acid = mannosamine + pyruvic acid.  N.B:-Addition of acetyl group (CH3-CO-) to neuraminic acid give the sialic acid ( the acetyl group is added to the N atom of mannosamine). And is called N-acetyl-neuraminic acid (NANA) 4.Aldonic acid:-  Definition:-It is an acid that results from oxidation of the aldhyde group of aldoses to carboxyl group.  Example  Gluconic acid from glucose.  Exam (mcq) 5.Uronic acid:- Definition:- It is an acid that results from oxidation of the primary alcohol group ( the last carbon) of aldoses to carboxyl group. Example :- Glucouronic acid from glucose. 6.Aldaric sugar:-  Definition:- It is an acid that results from oxidation of both aldhyde and primary alcohol groups of aldoses to carboxyl groups.  Example :- Glucaric (saccharic ) acid from glucose 7.Sugar alcohols:-  Definition:- Reduction of the carbonyl group (aldhyde or ketone group) gives the corresponding aclcohol.  Examples:- Sorbitol is the alcohol of glucose Sorbitol from glucose. Mannitol from mannose. Mixture of sorbitol and mannitol from fructose. 8.Inositols:- Definition :-  It is a sugar derived from cyclization of sugar alcohol mostly glucose.  It has 9 stereo isomeric forms.  It is regarded as member of B- complex vitamins. 9.Glycosides :- Exam Definition: - Glycosides are compounds resulting from condensation of sugars with another compound which may or may not be another sugar.  If the second compound is another monosaccharide the glycoside is called disaccharide.  If the second compound is not sugar. It is called aglycon which may be alcohol, phenol or base. Glycosidic bond may be :-  O-Glycosidic: - If the sugar is linked to OH group of the 2nd compound. Sugar Alchohol/ Phenol  N-Glycosidic:- If the sugar is linked to nitrogen atom of nitrogenous base e.g ribose + adenine in nucleotides. Sugar Base Impotance of Glycosides:-  Formation of disaccharides: - like maltose, lactose and sucrose if the 2nd compound is sugar.  Glycosides form many drugs that used for treatment of diseases.  Example: - digitalis is a cardiac glycoside used for treatment of heart failure. Exam