What are Carbohydrates? Aldoses and Ketoses

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1 What are Carbohydrates? Polyhydroxylated aldehydes and ketones Commonly called sugars General formula of common sugars!glucose: C 6 ( 2 ) 6!Glyceraldehyde: C 3 ( 2 ) 3 Talking points: C 2 ACS Division of Carbohydrate Chemistry Understanding carbohydrate coating Glucose of a bacterium Glucose leads to how antibodies and antibiotics work Glucose Fructose Cl 2 C C 2 Cl Fructose C 2 Cl Sucrose Sucralose (Splenda) Aldoses and Ketoses C C 2 D-mannose C 2 C 2 D-mannoketose triose: tetrose: pentose: hexose: 1

2 Glyceraldehyde C C 2 C C 2 C C 2 C C (R)-2,3-dihydroxypropanal D-(+)-glyceraldehyde (S)-2,3-dihydroxypropanal L-( )-glyceraldehyde Structures 2 and 3 are drawn in the original Fisher projection Structures 1 and 4 are drawn in the Victor-Meyer modification --Now commonly called the Fisher Projection The D and L designations D and L signify the relationship of a particular sugar to glyceraldehyde They do not designate the optical rotation of the sugar ptical Rotation is designated by the lowercase letters. i.e.! d or (+) for dextrorotary! l or ( ) for levorotary C C 2 D-(+)-glyceraldehyde C 2 C 2 D-( )-lactic acid C C C C 2 * C C C * C 2 A D-pentose An L-pentose 2

3 Drawing Fisher Projections of Monosaccharides 1. Draw aldehyde or ketone carbon at the top 2. Number from top to bottom 3. The asymmetric carbon of highest number is used to designate D or L C C 2 D-glucose Some Terms Methylol- Absolute configuration- Number of stereoisomers- Enantiomers- Diastereomers- Epimers- Anomers- 3

4 Types of Saccharides Monosaccharides- Disaccharides- ligosaccharides- Polysaccharides- C C C C C C C C C 2 C 2 C 2 C 2 C 2 C 2 C 2 C 2 D-(+)-Allose D-(+)-Altrose D-(+)-Glucose D-(+)-Mannose D-( )-Gulose D-(+)-Idose D-(+)-Galactose D-(+)-Talose C C C C C 2 C 2 C 2 C 2 D-( )-Ribose D-( )-Arabinose D-(+)-Xylose D-( )-Lyxose C C 2 D-( )-Erythrose The family of D-aldoses C C 2 D-( )-Threose C C 2 D-(+)-Glyceraldehyde 4

5 Cyclic Forms of Carbohydrates pyranoses C 2 Mixture of stereoisomers This is NT a C 2 D-allose C 2 C 2 D-allopyranose This is NT a C 2 Cyclic Forms of Carbohydrates furanoses and special Fisher projections C 2 D-allose C 2 C 2 S R C 2 C 2 aworth Projection D-allofuranose 5

6 aworth Formulas C 2 C 2 C 2 C 2 2 C C 2 C C 2 2 C D-Fructose Cyclic Isomers β-d-fructopyranose α-d-fructopyranose C 2 60% 8% C 2 * C 2 C 2 * C 2 β-d-fructofuranose 2% * * C 2 C 2 C 2 α-d-fructofuranose 30% 6

7 α-d-(+)-glucose k eq Mutarotation β-d-(+)-glucose [α] D +112 [α] D At equilibrium [α] D % of β, 36% of α and 0.003% of the open chain form + Reactions of Carbohydrates Glycoside formation/hydrolysis Ether formation (Ag 2 /C 3 I) Acetonide formation Ester formation (Ac 2, AcCl & pyridine) Reduction (NaB 4 ) Reducing/non-reducing sugers Methods of oxidation Silver oxide/ammonia (Tollens) Bromine/water Copper sulfate (Benedicts & Fehlings rgts) N 3 Periodic Acid/oxidative cleavage Kilani-Fisher Synthesis 7

8 Glycoside Formation/ydrolysis R' + R' R" R" R" R" :B :B R" R" Ether Formation Acetonide Formation 8

9 Ester Formation A reaction with an acid anhydride or acid chloride in the presence of a weak base leads to ester formation Reduction C 2 C C 2 NaB 4 then water workup C 2 C 2 mirror plane D-ribose ribitol/adonitol ($4/gram) xidation C C 2 C 2 Br 2, 2 C 2 D-( )-galactonic acid γ-lactone galactose galactonic acid Reducing & Nonreducing sugars i-pr 9

10 xidation Ag 2, N 4 Ag Tollen's CuS 4 Cu 2 Fehling's solution is prepared from solutions of copper(ii) sulfate, Rochelle salt (potassium sodium tartrate tetrahydrate), and Na Fehling's or Bendict's reagent Benedict's reagent is prepared from sodium carbonate, sodium citrate and copper(ii) sulfate. N 3 xidation (Aldaric Acids) Under vigorous conditions a dicarboxylic acid called an aldaric acid is formed 10

11 xidative Cleavage Kilani-Fisher Synthesis 11

12 Sucrose: A Disaccharide α-glucosidic linkage β-fructosidic linkage C 2 Glucose 2 C Fructose Lactose Polysaccarides The storage form of glucose in plants is called starch. The two forms of starch are amylose (20%) and amylopectin (80%) Amylose consists typically of more than 1000 D-glucopyranoside units connected by a linkages between C1 of one unit and C4 of the next Amylose adopts a very compact helical arrangement 12

13 Amylopectin Similar to amylose but has branching points every glucose units Branches occur between C1 of one glucose unit and C6 of another Glycogen (animal starch) Branches ~10 units Glycogen is a very large polysaccharide The large size of glycogen prevents if from leaving the storage cell The storage of tens of thousands of glucose molecules into one molecule greatly relieves the osmotic problem for the storage cell (this would be caused by the attempted storage of many individual glucose molecules) The highly branched nature of glycogen allows hydrolytic enzymes to have many chain ends from which glucose molecules can be hydrolyzed 13

14 Cellulose In cellulose, glucose units are joined by β-1,4 -glycosidic linkages Cellulose chains are relatively straight The linear chains of cellulose hydrogen bond with each other to give the rigid, insoluble fibers found in plant cell walls! The resulting sheets then stack on top of each other umans lack enzymes to cleave the β linkages in cellulose and so cannot use cellulose as 2 C Cellulose: makes up 90% of cotton and 50% of wood Chitin N N N 3 C 3 C 3 subunits of chitin 3 C R 3 C N P P N N Uridine diphosphate galactose N-Acetyl (UDP-GalNAc)+ glycosyltransferase A (GTA) 3 C Type Determinate: α-fucopyranose --> β-galactopyranose P P N N Uridine diphosphate galactose (UDP- Gal)+ glycosyltransferase B (GTB) 3 C 3 C N R R Type A Determinate: α-galactopyranose N-acetyl --> β-galactopyranose --> α-fucopyranose 3 C GTA and GTB differ by only 4 amino acids +/ blood is a result of the Rh factor agglutinogens JCE, 2005, 82 (12), 1846 Type B Determinate: α-galactopyranose --> β-galactopyranose --> α-fucopyranose 14