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Home , Aldose, Anomer, Monosaccharide, Osazone

Reactions of Monosaccharides Oxidation-Reduction Products Oxidation - Reduction H OH OH H OH OH [O] S R OH OH O O [O] = Ag+, NH , H O R R OH OH 3 2 OH OH or Br2 / H2O

Aldoses are "reducing" , that is, they are oxidized CHO CO H under very mild conditions. (Only the is oxidized.) 2 H OH + H OH Ag H OH OH HO H HO H [H] + Ag OH H OH H OH O H OH H OH OH OH [H] = ? CH OH CH OH 2 NaBH4 2 1) Identify the starting as D- or L-. 2) Draw Fisher projections for the products. 3) Draw a of the beta pyrano . Sorbitol

Redox Reactions of Monosaccharides

Oxidation In a basic solution, are converted into

Ketones and alcohols cannot be oxidized by Br2 Formation A strong oxidizing agent such as HNO can oxidize the 3 Aldoses and ketoses react with three equivalents of aldehyde and the alcohol groups phenylhydrazine

The C-2 of aldoses form identical Reaction of Ketoses with Phenylhydrazine

The chain of an can be increased by one The Ruff degradation shortens an aldose chain by one carbon in a Kiliani–Fischer synthesis carbon Preparation of the Calcium D-Gluconate for the Monosaccharides Ruff Degradation D- beta anomer O CHO OH H OH HO H O HO H OH H OH OH H OH OH CH OH all groups are equatorial 2 or 1,2 - trans to each other OH HOCH2 O OH HO HO

Cyclic Structure of Monosaccharides Note … Formation

• 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 , a hemiacetal, or a hemiacetal group is a

anomer anomer

The of pure α-D-glucose or β-D-glucose changes over time to reach an equilibrium ()

Monosaccharides ester formation Acylation of Monosaccharides CHO O O H OH CH3CO2 O2CCH3 HO H O H3CO O OCH3 H OH O2CCH3 alpha + anomer H OH O2CH3 O CCH CH2OH 2 3 O2CCH3 CH3CO2CH2 O O2CCH3 CH3CO2 CH3CO2 Reactions of Monosaccharides Alkylation of the OH Groups (acetal) formation

H OH OH O OCH3 HO OH CH3OH O + H HO OH OH OH CH3OH OH + + H H OH O HOCH2CH OCH3

HO OH

Mechanism of Glycoside Formation

Formation of

The acetal (or ketal) of a sugar is called a glycoside

The formation of a glycoside favors the α-glucoside Reactions of Monosaccharides product: the Acetonide (acetal) formation

CH3 O OH cis CH3 O O O OH O OH HCl O + H3C CH3

HO O OH OH CH trans H3C 3 Composed of two subunits hooked Formation of an N-Glycoside together by an acetal linkage

In α-, the OH group bonded to the anomeric carbon is axial

Maltose is a reducing sugar

In , the two subunits are hooked together by a In , the two different subunits are joined by a β-1,4’-glycosidic linkage β-1,4’-glycosidic linkage

Cellobiose is a reducing sugar Lactose is a reducing sugar

The most common is is a component of

Sucrose is not a reducing sugar is another component of starch that has a branched structure

An example of a naturally occurring product derived from Monosaccharides Identification: 1H NMR couplings

Examples Dihedral angles 1,2-disubstituted cyclohexanes Coupling Constants Using Coupling Values

• A mixture of 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 Dihedral Angles

• Given a Haworth structure: a) draw the Fisher structure of the open straight chain, identify it as: eg. aldose, , 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 : 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. The larger coupling constant corresponds to the larger dihedral angle. Therefore X is alpha.

Olestra, Fats & http://www.cspinet.org/olestra/ OH HO OH OH O HO OH HO O O

HO OOCH3 CH3COO OOCCH 3 OOCCH3 O CH3COO

OOCCH3 CH COO O 3 O

Olestra CH3COO

R Can Be: O ( ) O ( ) O ( )

Simplesse

O CH2OH O H H N N ( N ) H CH3 O CH2CH2CO2H