chapter 17 carbohydrates (糖,碳水化合物)
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Chapter 17 Carbohydrates (糖,碳水化合物). Ref: Wade, chapter 23 曾昭琼,第十九章. Carbohydrates ( 糖,碳水化合物 ). D-glucose ( 葡萄糖 ). D-fructose ( 果糖 ). Sugars ( 糖 ). They have the molecular formulas C n (H 2 O) n. Carbohydrates ( 糖,碳水化合物 ). - PowerPoint PPT PresentationTRANSCRIPT
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Chapter 17CarbohydratesRef: Wade, chapter 23
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Carbohydrates ()They have the molecular formulas Cn(H2O)nD-glucose ()D-fructose ()Sugars ()
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Polyhydroxyaldehydes, polyhydroxyketones, and compounds that can be hydrolyzed to them are classified as carbohydrates Carbohydrates ()(glucose)(fructose)(galactose)(sucrose)(maltose)(lactose)(starch)(cellulose)
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Classification of carbohydrates monosacharides : simple sugar (glucose)(fructose)(galactose) disaccharides (sucrose)(maltose)(lactose) oligosaccharides polysaccharides (starch)(cellulose)
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Monosaccharides
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Polyhydroxy aldehydes are aldoses Polyhydroxy ketones are ketoses 1. Classification of Monosaccharides trioses tetroses pentoses hexoses heptoses aldohexoseketohexose
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D-glucoseD- D/L: D and L notations are used to describe the configurations of carbohydrates ()L-glucoseL-
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2. Structures of monosaccharidesRelative configuration erythreo- /threo- /Absolute configuration R- /S-D- /L- Open-chain structure Cyclic structure
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D-D-D-Family tree of D-aldosesref: 19-1 or figure 23-3D-D-D-D-D-D-D-
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epimers epimers
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Cyclic Structures of Monosaccharides----Hemiacetal FormationHaworth formulasHaworth formulasanomer Anomeric carbon-D-(+)-glucopyranose-D - (+)-glucopyranose
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1-D-(glucose)
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D-(glucose)Drawing cyclic monosaccharides
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b-D-glucose is the predominant form at equilibrium-D-(+)-glucopyranose-D - (+)-glucopyranosetrans-, -cis-, -
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D-glucopyranoseD--D-glucopyranose-D--D-glucopyranose-D-
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D-ribofuranoseD--D-ribofuranose-D- -D-ribofuranose -D-
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If an aldose can form a five- or six-membered ring, it will exist predominantly as a cyclic hemiacetal Six-membered rings are called pyranoses Five-membered rings are called furanosesNote b- sugar is the predominant form at equilibrium. Haworth projections allow us to see the relative orientation of the OH groups in the ring.
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D-fructose()
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mutarotation ()a property of anomersAt equilibrium, []D25 = +52.6 , including - 36% - 64%At equilibrium, []D25 = +52.6 , including - 36% - 64%
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3. Reactions of monosaccharides(1) Side reactions in base: epimerization; enediol rearrangement(2) Reduction: NaBH4 ; H2/catalyst, forming alditols ()(3) Oxidation: Bromine water (Br2-H2O); forming aldonic acid (glyconic acid, ) HNO3; forming aldaric acid () Tollens test; Feillings reagent; (4) Formation of glycosides(5) Etherification(6) Acylation: ester formation(7) Reaction with phenylhydrazines: osazones () formation(8) Chain shortening: the Ruff degradation(9) Chain lengthening: the Kiliani-Fischer synthesis-C=O, -OH
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Side reactions in base: --------epimerization; enediol rearrangement ()() 23-8epimerizationD-glucoseD-D-mannoseD-
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enediol rearrangementD-glucoseD-D-mannoseD-D-fructoseD-
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(2) Reduction of MonosaccharidesThe carbonyl of aldoses and ketoses can be reduced bythe carbonyl-group reducing agents to form alditols()23-9
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(3) Oxidation of monosaccharides; reducing sugarsA) Br2-H2OThe aldehyde groups can be oxidizedKetones and alcohols cannot be oxidized by Br2Br2-H2O can be used to determine aldehydes and ketones 23-10
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B) Nitric acid (HNO3)
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Sugars that reduce Tollens reagent to give a silver mirror are called reducing sugar(). C) Tollens test: Ag(NH3)2+
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D) Periodic acid (HIO4) cleavage of sugars
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(4) Formation of glycosides ()The acetal (or ketal) of a sugar is called a glycoside.methyl -D-glucopyranoside(--D-(+)- )(mp, 165 []D25 = +158)methyl -D-Glucopyranoside(- -D-(+)- )(mp, 107 []D25 = -33)Nonreducing sugars
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Mechanism of Glycoside Formation
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Formation of an N-Glycoside
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(5) Etherification Methyl 2,3,4,6-tetra-O-methyl--D-glucopyranosideReagents: CH3OSO3CH3-NaOH; CH3I-Ag2O2,3,4,6-tetra-O-methyl-D-glucose(2,3,4,6--O-
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(6) Acylation: ester formationReagents: RCOCl or RCOOCOR, base;
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Reaction with phenylhydrazines: ------osazones () formationosazones ()D-mannoseD-D-fructoseD-D-mannoseD-
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(8) Chain shortening: the Ruff degradation()The Ruff degradation is used mainly for determination and synthesis of new sugars.
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(9) Chain lengthening: the Kiliani-Fischer synthesisThis method is used for synthesis of new sugars.
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(1) Fishers proof of the configuration of glucose4. Determination of the structure of monosaccharidesD-glucoseD-mannoseD-arabiosedegradationD-erythroseHNO3Meso-tartaric acidOptically active productHNO3degradation
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(2) Determination of Ring SizeThe size of the ring can be determined from the structure of the open-chain formApproach 1
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Approach 2An acetal of the monosaccharide is oxidized with excess HIO4+ CH3OH
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Problem:
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5. Disaccharides
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Which is a nonreducing sugar?
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6. PolysaccharidesAmylosestarch
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Amylopectin
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cellulose
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Blood type is determined by the nature of the sugar bound to the protein on the surface of red blood cells
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7. Nuleic acids
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pentose ribose deoxyribose ribonucleosides deoxyribonucleosides
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(base) uracil (U) cytosine (C) adenine (A) guanine (G) thymine(T)
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RNA 19
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ribonucleic acid35
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DNAdeoxyribonuleic acids
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ContentsClassification of carbohydratesMonosaccharides Classification Structure chain: configuration: D,L-; erythro/threo; cyclic structure: -,-; mutarotation Reactions oxidation: tollens reagent, Br2-H2O; HNO3; HIO4 reduction: NaBH4 formation of osazones formation of glycosides acylation etherification chain shorting (degradation) and lengthening Fischers proof of the configuration of glucose determination of ring size DisaccharidesPolysaccharidesNucleic acids
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Assignments 23-54, 57, 59, 63, 66, 6769