Carbohydrates

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Carbohydrates
Monosaccharides Formula CnH2nOn
n3-8
Name Formula Triose
C3H6O3 Tetrose
C4H8O4 Pentose C5H10O5 Hexose
C6H12O6 Heptose
C7H14O7
Aldose - aldehyde/hydroxyl Ketose
ketone/hydroxyl
glyceraldehyde

• (S)
• (D) (L)
• 13.50 -13.50

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Penultimate Carbon stereocenter on the next to
the last carbon on the chain. Used as
reference point for naming other monosaccharides
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Cyclic Structures monosaccharides exist almost
exclusively as 5- and 6-membered cyclic
hemiacetals.
Recall
aldehyde hemi-acetal
acetal
anomeric carbon
? - OH is down
? - OH is up
D-Glucopyranose
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How many stereoisomers are there for aldohexoses?
Answer 24 16
Who determined the stereochemistry of glucose?
Emil Fischer 1852 1919 Nobel Prize 1902
Fischers Proof of Glucose stereochemistry stands
as a monument to chemical ingenuity and
intellect.
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Oxidation of Sugars Aldaric Acids
Formation of Osazones Epimers
The stereochemistry at C-2 is destroyed. Thus
aldoses that differ only at C-2 will produce
identical osazones.
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The Kiliani-Fischer Synthesis Buildin' 'em up.
Epimers diastereomers that differ only at one
stereocenter.
Step 1 Reaction of aldehyde with cyanide to form
cyanohydrin Step 2 Base hydrolysis of cyano
group to carboxylic acid Carboxylic
acid reacts to OH to form lactone (cyclic
ester) Step 3 Lactone is reduced with Na metal to
form aldehyde again
Bottom Line the Kiliani-Fischer synthesis
converts an aldose into two epimeric aldoses
which each contain one more carbon
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The Ruff Degradation Tearin' 'em down
Bottom Line C1 is lost as CO2 and C2 becomes the
carbonyl carbon in the new
sugar
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D-Glucose- a cyclic monosaccharide
?-D-glucopyranone Open Chain
?-D-glucopyranone
? 18.70

1120 Equilibrium 64 36
Observation A fresh sample of the ?-form shows
an initial rotation of 1120 which
gradually decreases to 52.70. Why?
Mutorotation Change in specific rotation that
accompanies the interconversion of ? and ?-
anomers in water.
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Other Reactions of Monosaccharides
1. Glycoside Formation
CH3OH

• Stable in water
• Does not undergo
• mutorotation

H
Acetal
Hemi-acetal
N-glycoside
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2. Reduction to Alditols
H2, Ni
D-Glucose
D-Glucitol
D-Sorbitol (sweetener)
3. Oxidation of Aldonic Acids
AgNO3, NH4OH
Ag
(Tollens Reagent)
silver mirror
Reducing Sugar
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Aldoses are considered reducing sugars but
ketones are considered nonreducing Sugars? Why
the difference?
Answer Ketones cannot be oxidized like
aldehydes.
AgNO3, NH4OH
No Reaction
Nonreducing
Nonreducing
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Disaccharides consists of two monosaccharides
joined by a glycoside bond. Maltose
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(No Transcript)
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Oligosaccharide 3 to 10 monosaccharides Raffino
se (3) Stachyose (4) Verbascose (5)
The galactose units are cleaved by
alpha-galactosidase, and the glucose-fructose
link in sucrose is hydrolyzed by sucrase (or
invertase). Humans do not have a source of
alpha-galactosidase in their digestive system, so
the oligosaccharide passes largely unchanged
into the colon. Anerobic microorganisms in the
colon ferment these sugars, producing carbon
dioxide and methane
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7 glucopyranose rings connected by ?-1,4-linkage
Cyclodextrins are formed when starch is treated
with an amylase enzyme from Bacillus macerans.
They have a hydrophobic cavity and they can
encapsulate small nonpolar organic molecules
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Polysaccharides
(C6H10O5)n where n ranges from 500 to 5,000 MW
8100 to 810,000
Most animals cannot digest cellulose as a food,
and in the diets of humans this part of our
vegetable intake functions as roughage and is
eliminated largely unchanged. Some animals (the
cow and termites, for example) harbor intestinal
microorganisms that breakdown cellulose into
monosaccharide nutrients by the use of
beta-glycosidase enzymes
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20
80
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1H NMR
cholesterol
How do you make assignments? Use 2-Dimensional
NMR!
13C NMR