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Monosaccharides Reactions of Monosaccharides Oxidation-Reduction Products Oxidation - Reduction OH H OH OH H S OH [O] OH O [O] = Ag+, NH3, H2O or Br2 / H2O OH R OH OH Aldoses are "reducing" sugars, that is, they are oxidized under very mild conditions. (Only the aldehyde is oxidized.) OH OH [H] OH O OH OH [H] = ? HO H H OH H R CO2H Ag + OH H OH HO H H OH CH2OH 1) Identify the starting sugar as D- or L-. 2) Draw Fisher projections for the products. 3) Draw a Haworth projection of the beta pyrano anomer. R OH CHO H H OH O H NaBH4 + Ag OH OH CH2OH Sorbitol Redox Reactions of Monosaccharides Oxidation Ketones and alcohols cannot be oxidized by Br2 In a basic solution, ketoses are converted into aldoses Osazone Formation A strong oxidizing agent such as HNO3 can oxidize the aldehyde and the alcohol groups The C-2 epimers of aldoses form identical osazones The carbon chain of an aldose can be increased by one carbon in a Kiliani–Fischer synthesis Aldoses and ketoses react with three equivalents of phenylhydrazine Reaction of Ketoses with Phenylhydrazine The Ruff degradation shortens an aldose chain by one carbon Monosaccharides Preparation of the Calcium D-Gluconate for the Ruff Degradation D-glucose beta anomer O CHO H HO OH HO H H OH H OH H O OH OH OH all groups are equatorial or 1,2 - trans to each other CH2OH HOCH2 HO Cyclic Structure of Monosaccharides Hemiacetal Formation OH O OH OH HO Note … • If an aldose can form a five- or six-membered ring, it will exist predominantly as a cyclic hemiacetal • A sugar with an aldehyde, a ketone, a hemiacetal, or a hemiacetal group is a reducing sugar anomer anomer The specific rotation of pure α-D-glucose or β-D-glucose changes over time to reach an equilibrium (mutarotation) Monosaccharides ester formation Acylation of Monosaccharides CHO H HO O OH H H OH H OH H3CO O O CH2OH CH3CO2CH2 O CH3CO2 CH3CO2 CH3CO2 OCH3 O2CCH3 O O2CCH3 O 2CH3 O2CCH3 O2CCH3 O2CCH3 + alpha anomer Reactions of Monosaccharides Alkylation of the OH Groups Glycoside (acetal) formation H OH OH O OH H OH + HO CH3OH H + H OH HOCH2CH HO OCH3 HO CH3OH OH O O + OH OH OCH3 OH Mechanism of Glycoside Formation Formation of Glycosides The acetal (or ketal) of a sugar is called a glycoside The formation of a glycoside favors the α-glucoside product: the anomeric effect Reactions of Monosaccharides Acetonide (acetal) formation CH3 OH cis O OH O OH + H3C CH3 HO O O O HCl O OH trans H3 C O OH CH3 CH3 Disaccharides Formation of an N-Glycoside Composed of two monosaccharide subunits hooked together by an acetal linkage In α-maltose, the OH group bonded to the anomeric carbon is axial Maltose is a reducing sugar In cellobiose, the two subunits are hooked together by a β-1,4’-glycosidic linkage In lactose, the two different subunits are joined by a β-1,4’-glycosidic linkage Cellobiose is a reducing sugar Lactose is a reducing sugar The most common disaccharide is sucrose Polysaccharides Amylose is a component of starch Sucrose is not a reducing sugar Amylopectin is another polysaccharide component of starch that has a branched structure An example of a naturally occurring product derived from carbohydrates Monosaccharides Identification: 1H NMR couplings Examples 1,2-disubstituted cyclohexanes Dihedral angles Coupling Constants Using Coupling Values • A mixture of anomers of D-glucose was separated and analyzed by nmr. • The coupling constants of the epimeric protons were 3.5 Hz for anomer X and 8.6 Hz for anomer Y. • Identify the alpha and beta anomer. Possible Exam Questions • Given a Haworth structure: a) draw the Fisher structure of the open straight chain, identify it as: eg. aldose, pentose, reducing, etc. b) draw a Haworth structure for the opposite anomer of the given structure, c) draw the most stable chair conformer, is it the α- or β-? • Identify an isomer: D- or L- from a structure. How many possible stereoisomers could the structure possibly have? • Give an example of mutarotation. • Identify/name structures: saccharides, glycosides, glycosamine, etc. Olestra, Fats & Lipids http://www.cspinet.org/olestra/ HO OH OH OH O HO OH HO O O HO CH3COO OOCH3 OOCCH3 OOCCH3 O CH3COO OOCCH3 O CH3 COO O Olestra CH3COO R Can Be: O ( ) O ( ) O ( ) Simplesse H O (N CH3 N H CH2OH H N O O ) CH2 CH2CO2 H Dihedral Angles The larger coupling constant corresponds to the larger dihedral angle. Therefore X is alpha.