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.