Chapter 17CarbohydratesRef: Wade, chapter 23

Carbohydrates ()They have the molecular formulas Cn(H2O)nD-glucose ()D-fructose ()Sugars ()

Polyhydroxyaldehydes, polyhydroxyketones, and compounds that can be hydrolyzed to them are classified as carbohydrates Carbohydrates ()(glucose)(fructose)(galactose)(sucrose)(maltose)(lactose)(starch)(cellulose)

Classification of carbohydrates monosacharides : simple sugar (glucose)(fructose)(galactose) disaccharides (sucrose)(maltose)(lactose) oligosaccharides polysaccharides (starch)(cellulose)

Monosaccharides

Polyhydroxy aldehydes are aldoses Polyhydroxy ketones are ketoses 1. Classification of Monosaccharides trioses tetroses pentoses hexoses heptoses aldohexoseketohexose

D-glucoseD- D/L: D and L notations are used to describe the configurations of carbohydrates ()L-glucoseL-

2. Structures of monosaccharidesRelative configuration erythreo- /threo- /Absolute configuration R- /S-D- /L- Open-chain structure Cyclic structure

D-D-D-Family tree of D-aldosesref: 19-1 or figure 23-3D-D-D-D-D-D-D-

epimers epimers

Cyclic Structures of Monosaccharides----Hemiacetal FormationHaworth formulasHaworth formulasanomer Anomeric carbon-D-(+)-glucopyranose-D - (+)-glucopyranose

1-D-(glucose)

D-(glucose)Drawing cyclic monosaccharides

b-D-glucose is the predominant form at equilibrium-D-(+)-glucopyranose-D - (+)-glucopyranosetrans-, -cis-, -

D-glucopyranoseD--D-glucopyranose-D--D-glucopyranose-D-

D-ribofuranoseD--D-ribofuranose-D- -D-ribofuranose -D-

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.

D-fructose()

mutarotation ()a property of anomersAt equilibrium, []D25 = +52.6 , including - 36% - 64%At equilibrium, []D25 = +52.6 , including - 36% - 64%

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

Side reactions in base: --------epimerization; enediol rearrangement ()() 23-8epimerizationD-glucoseD-D-mannoseD-

enediol rearrangementD-glucoseD-D-mannoseD-D-fructoseD-

(2) Reduction of MonosaccharidesThe carbonyl of aldoses and ketoses can be reduced bythe carbonyl-group reducing agents to form alditols()23-9

(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

B) Nitric acid (HNO3)

Sugars that reduce Tollens reagent to give a silver mirror are called reducing sugar(). C) Tollens test: Ag(NH3)2+

D) Periodic acid (HIO4) cleavage of sugars

(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

Mechanism of Glycoside Formation

Formation of an N-Glycoside

(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-

(6) Acylation: ester formationReagents: RCOCl or RCOOCOR, base;

Reaction with phenylhydrazines: ------osazones () formationosazones ()D-mannoseD-D-fructoseD-D-mannoseD-

(8) Chain shortening: the Ruff degradation()The Ruff degradation is used mainly for determination and synthesis of new sugars.

(9) Chain lengthening: the Kiliani-Fischer synthesisThis method is used for synthesis of new sugars.

(1) Fishers proof of the configuration of glucose4. Determination of the structure of monosaccharidesD-glucoseD-mannoseD-arabiosedegradationD-erythroseHNO3Meso-tartaric acidOptically active productHNO3degradation

(2) Determination of Ring SizeThe size of the ring can be determined from the structure of the open-chain formApproach 1

Approach 2An acetal of the monosaccharide is oxidized with excess HIO4+ CH3OH

Problem:

5. Disaccharides

Which is a nonreducing sugar?

6. PolysaccharidesAmylosestarch

Amylopectin

cellulose

Blood type is determined by the nature of the sugar bound to the protein on the surface of red blood cells

7. Nuleic acids

pentose ribose deoxyribose ribonucleosides deoxyribonucleosides

(base) uracil (U) cytosine (C) adenine (A) guanine (G) thymine(T)

RNA 19

ribonucleic acid35

DNAdeoxyribonuleic acids

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

Assignments 23-54, 57, 59, 63, 66, 6769