Carbohydrate Chemistry PDF

Carbohydrate chemistry D/ Eman Abd elmaksoud Lecturer of Biochemistry Naming or nomenclature of monosaccharides: 1- According to the presence of aldehyde or ketone group. 2- According to the number of carbon atoms. 3- According to both presence of aldehyde or ketone gr...

Carbohydrate chemistry D/ Eman Abd elmaksoud Lecturer of Biochemistry Naming or nomenclature of monosaccharides: 1- According to the presence of aldehyde or ketone group. 2- According to the number of carbon atoms. 3- According to both presence of aldehyde or ketone group and number of carbon atoms. 1- According to the presence of aldehyde or ketone group: *Aldoses (aldo sugar): monosaccharides containing aldehyde group (-CHO). The suffix -ose means sugar. *Ketoses (keto sugar): monosaccharides which containing ketone group (-C=O).  2- According to the number of carbon atoms: Trioses: monosaccharides containing 3 carbon atoms. Tetroses: monosaccharides containing 4 carbon atoms. Pentoses: monosaccharides containing 5 carbon atoms. Hexoses: monosaccharides containing 6 carbon atoms. Heptoses: monosaccharides containing 7 carbon atoms. 3-According to both presence of aldehyde or ketone group and number of carbon atoms: Aldotrioses and ketotrioses. Aldotetroses and ketotetroses. Aldopentoses and ketopentoses. Aldohexoses and ketohexoses. Classification of monosaccharides: 1- Triosese: monosaccharide containing 3 carbon atoms. Aldotrioses: Glyceraldehyde (glycerose).parent sugar Ketotrioses: Dihydroxyacetone. 2- Tetroses: monosaccharide containing 4 carbon atoms. Aldotetroses: Erythrose. Ketotetroses: Erythrulose. Erythulose Erythrose 3-Pentoses: monosaccharide containing 5 carbon atoms. Aldopentoses: Ribose, arabinose, xylose and lyxose. Ketopentoses: Ribulose and xylulose. 4- Hexoses: monosaccharide containing 6 carbon atoms. Aldohexoses: Glucose, galactose and mannose. Ketohexoses: Fructose.  Ring (cyclic) structure of sugars: The simple open chain formula of sugars fails to explain some reactions e.g. glucose which has aldehyde group, doesn't give all the reactions of aldehyde. This indicates that the –CHO group must be masked or combined in some way. In solution, the sugar which has an aldehyde group undergoes the following: 1- Hydration of aldehyde group to form aldenol group (alcohol). 2- Condensation between one of the –OH of aldenol group and the –OH group of C4 or C5 to form ring structure (hemiacetal structure). 3- If the remaining –OH is on the right side, so it is α- sugar. 4- If the remaining –OH is on the left side, so it is β-sugar. 5- Pyranose and furanose: a) The 1-5 ring form is called pyranose as it resembles an organic compound named pyran e.g. α and β glucopyranose. b) The 1-4 ring form is called furanose as it resembles an organic compound named furan e.g. α and β glucofuranose. 5- Haworth and chair forms:  Asymmetric carbon atom: It is that carbon atom which is attached to 4 different groups or atoms. Any substance containing asymmetric carbon atom shows two properties; optical activity and optical isomerism. (ɗ) or (+) (ℓ) or (-)  If the concentration of the substance and the length of the tube are fixed, the angle of rotation will depend only on the nature of the substance and it is called specific rotation. Specific rotation: it is the angle of rotation specific for each optically substance when the concentration of substance is 100 g/dl and the length of measuring tube is 10 cm using sodium light at 20 ₒC. Example of specific rotation for glucose is (+52.5) and for fructose is (-91).  B- Optical isomerism: It is the ability of substance to present in more than one form (isomer). A substance containing one asymmetric carbon atom has 2 isomers. A substance containing 2 or more asymmetric carbon atoms can exist in a number of isomers = 2n where n is the number of asymmetric carbon atoms. e. g. glucose has 4 asymmetric carbon atoms so the number of its isomers equal 16 isomers.  1- D and L isomers (Enantiomers): Enantiomers are pairs of compounds that have the same structural formulas but differ in spatial configuration. one of them is the mirror image of the other and they rotate the plane of polarized light equally but in opposite directions. The simplest monosaccharide glyceraldehyde has one asymmetric carbon. So it has 2 optically active forms: L and its mirror image D form  They are classified into D and L forms according to the position of –OH attached to the carbon atom next to last –CH2OH e.g. carbon atom number 5 in glucose. 2- Anomeric carbon and anomers: Anomeric carbon: is the asymmetric carbon atom obtained from active carbonyl sugar group: carbon number 1 in aldoses and carbon number 2 in ketoses. Anomers: these are isomers obtained from the change of position of OH attached to the anomeric carbon e.g. α and β glucose are 2 anomers.  Mutarotation: It is a gradual change of specific rotation of any optically active substance having free aldehyde or ketone group. -α-glucose freshly dissolved in water, has specific rotation of +112. -β-glucose when freshly dissolved in water, has specific rotation of +19. When both anomers are left for sometimes α and β sugars slowly change into an equilibrium mixture which has specific rotation of +52.5  3- Aldose-Ketose isomerism: Fructose has the same molecular formula as glucose but differs in structure formula. One contains keto group (fructose) and the other contains aldehyde group (glucose). Both are isomers. Other examples of aldoses-ketose isomers include: D-glyceraldehyde and dihdroxyacetone, D-ribose and D-ribulose, D-xylose and D-xylulose.  4- Epimeric carbon and epimers: Epimeric carbon is the asymmetric carbon atom other than carbon of aldehyde or ketone group e.g. carbons number 2, 3 and 4 of glucose. Epimers: are isomers due to difference in configuration at a single carbon atom (epimeric carbon atom). so, D-glucose and D-galactose are epimers (C4). D-glucose and D-mannose are also epimers (C2). but D-galactose and D-mannose are not epimers since they differ at C2-4.  Properties of monosaccharides: A) Physical properties: 1. All monosaccharides are soluble in water. 2. All monosaccharides show the property of optical activity. 3. All monosaccharides can exist in α and β forms. 4. All monosaccharides can undergo mutarotation.