7p1-1 monosaccharides monosaccharide stereoisomers cyclic structures reactions examples and...
DESCRIPTION
7P Monosaccharides polyhydroxy Aldehydes are aldoses Ketones are ketoses 3=triose 4=tetrose 5=pentose 6=hexose Number of carbonsTRANSCRIPT
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7P1-1
MonosaccharidesMonosaccharide stereoisomersCyclic structuresReactionsExamples and derivatives
Di and oligosaccharidesPolysaccharides
Homo and heteropolysaccharidesGlycoconjugates
Chapter 7: Outline
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7P1-2
Originally, carbohydrates were those compounds having the formula Cn(H2O)n. Only monosaccharides or simple sugars fit the formula. As more complex carbohydrates were discovered, the term came to mean compounds associated with polyhydroxy aldehydes and ketones.
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7P1-3
7.1 Monosaccharides
polyhydroxy
Aldehydesare aldoses
Ketonesareketoses
3=triose4=tetrose5=pentose6=hexose
Number of carbons
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7P1-4
Monosaccharides: generic namesThe generic name for a simple sugar
begins with the carbonyl prefix aldo or keto and ends with the term for the number of carbons.
An aldose with three carbons is called an aldotriose. A ketose with three carbons is a ketotriose.
What is the name for a six carbon aldehyde sugar?What is the name for a five carbon ketone sugar?
aldohexose
ketopentose
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7P1-5
DihydroxyacetoneDihydroxyacetone
Is a ketotriose
CH2OHCCH2OH
O
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7P1-6
GlyceraldehydeGlyceraldehydeIs an aldotriose C
C
O H
CH2OHOHH
Glyceraldehyde exists in two stereoisomeric forms because the starred carbon is a stereocenter: it hasfour different groups attached.
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7P1-7
The stereoisomers of glycer-aldehyde are designated D or L. The D isomer has the OH on the stereocenter to the right. The L isomer has the OH on the left .
CC
O H
CH2OHOHH
CC
O H
CH2OHHOH
the D isomer the L isomer
stereocenter
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7P1-8
Glyceraldehyde: 3The stereoisomeric forms of glycer-
aldehyde are enantiomers: nonsuper-imposable mirror image molecules.
Perspective drawings of the two enantiomers of glyceraldehyde are on the next slide. A stereo view is on slide 11.
Remember, barred bonds ( ) recede behind the plane of the screen and wedge ( ) bonds project in front of the plane.
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7P1-9
Perspective View
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7P1-10
Carbonyl group
CH2OH group
OH groupH atom
View with blue lens on the left eye.
Stereoscopic view of glyceraldehyde
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7P1-11
Fischer ProjectionsIn a Fischer projection, the
sugar molecule is oriented so that the most oxidized carbon is to the top. The stereocenter carbons are arranged so that the groups not part of the main chain project horizontally toward the viewer.
The molecule is in the all eclipsed form.
CO H
CH OHCCH2OH
H OH
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7P1-12
Monosaccharides are drawn in Fischer projections with the most oxidized carbon closest to the top. The carbons are numbered from the top. If the the stereocenter with the highest number has the OH to the right, the sugar is D. If the OH is to the left, the sugar is L.
Most common sugars are in the D form.Note: Fisher projections represent an all
eclipsed conformation.
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7P1-13
1
2
3
4
1
2
3
4
565
CC
O H
COHH
CH OHH
CH2OHOH
CH2OHCC
OOH
C OHHC
H
H OHCH2OH
D-ribosean aldopentose
D-fructosea ketohexose
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7P1-14
CHOCC
OHOH
C HOHC
H
H OHCH2OH
H
D-glucosean aldohexose
D-galactosean aldohexose
CHOCC
OHOH
C OHHC
H
H OHCH2OH
H
These diastereomers are also epimers, they differ in configuration at only one stereo-center (colored dot).
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7P1-15
Cyclic forms for sugarsMost simple sugars of four or more
carbons exist in the cyclic (hemiacetal or hemiketal) form.
A hydroxy group in the sugar reacts with the carbonyl group.
The new OH bearing carbon is now a stereo center and is called an anomeric carbon.
If the OH on the ring is “up” the carbon is , if the OH is “down” it is .
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7P1-16
Cyclic forms for sugars-2 Fischer projections for D glucose
CCC
OHOH
C OHHC
H
HCH2OH
HOH
OH
CCC
OHOH
C OHHC
H
HCH2OH
HOHH C
CC
OHOH
C OHHC
H
HCH2OH
HOH H
D-glucose D-glucosecyclic form
O
D-glucosecyclic form
O
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7P1-17
Cyclic forms for sugars-3 Haworth1. Draw a five- or six-membered ring
O O
pyranose form furanose form2. Anomeric C to right of O. Place OH up or down. Left on Fischer, up on ring.3. In D- sugars, the last C is always up.
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7P1-18
Cyclic forms for sugars-4 HaworthCH2C O
OH
COH HC OHHCHCH2OH
OH
O
CH2OH
OHOH
OH
CH2OH
D-fructose-D-fructofuranose+ isomer
Anomeric C-OH
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7P1-19
Cyclic forms for sugars-5 Glucose
Pyranose ring form
OCH2OH
HH
OHHOH
OHH
O
H
HOCH2OH
HH
OHHOH
OHH O
HH
OCH2OH
HH
OHHOH
OH
HH
O H
form(alpha)
form(beta)
arrows showelectron movement
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7P1-20
Cyclic forms for sugars-6The alpha and beta forms of cyclic
sugars are said to be anomers. They differ in configuration about the hemiacetal or hemiketal carbon.
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7P1-21
Cyclic forms for sugars-7Ribose also exists mainly in the cyclic
form.
OCH2OH
H
HH
OH
H
OH
O
HCH2OH
HH
OH
H
OH
O
H
O H
D-ribose D-ribofuranose(furanose ring form)
arrows showelectron movement
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7P1-22
D-glucose: the chair conformer
OH
HH
H
HOH
H
O
OHOH
CH2OH
12
3
45
6
Four of the five bulky groups (OH and CH2OH on C 2,3,4,5) on the ring are in the more stable equitorial positions!
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7P1-23
Oxidation of Monosaccharides
OCH2OH
HH
OHH
OH
OH
H OO
CH2OH
HH
OHH
OH
OH
HOH
H
Aldoses react with Tollen’s reagent (Ag(NH3)2+) to give a
lactone (cyclic ester). The silver ion plates out as a mirror.
Ag(NH3)2+
+ Ag(mirror)
Cu2+
+ Cu2O (red-orange)Benedict’s reagent (a blue copper ion solution) also gives a lactone. The blue color fades as reaction occurs.
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7P1-24
Aldehyde oxid’naldonic acid
Oxidation of Monosaccharides-2COOHCC
OHOH
C OHHC
H
H OHCH2OH
H
D-gluconic acid
Term CH2OH oxid’n
uronic acid
CHOCC
OHOH
C OHHC
H
H OHCOOH
H
D-glucuronic acid
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7P1-25
Oxidation of Monosaccharides-3Aldehyde + term CH2OH oxid’n
aldaric acid COOHCC
OHOH
C OHHC
H
H OHCOOH
H
D-glucaric acid
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7P1-26
Reduction of MonosaccharidesThe most important reduced sugar is deoxyribose. (In DNA)
When the carbonyl of a sugar is reduced to an alcohol, alditols are produced. The two shown above are used to sweeten nonsugar gum.
D-sorbitol D-xylitol
CH2OHCC
OHOH
C HOHC
H
H OHCH2OH
H
CH OHCH2OH
CH2OHCC
OHOH HHC
C
O H
CHH
CH OH
OHHCH2OH
D-deoxyribose
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7P1-27
Isomerization
Isomerization of mono-saccharides occurs through an enediol.
CCC
OHOH
C OHHC
H
H OHCH2OH
HH O C
CC
OHOH
C OHHC
H
H OHCH2OH
H OH
CH2CC
OOH
C OHHC
H
H OHCH2OH
OH
CCC
OHOH
C OHHC
H
H OHCH2OH
HH O
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7P1-28
Esters of MonosaccharidesThe OH groups of sugars can react with
phosphoric acid to give phosphate esters.
OCH2OPO3
2-
HH
OHH
OH
OH
HH
OH
D-glucose-6-phosphate
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7P1-29
GlycosidesThe anomeric OH can react with another
OH on an alcohol or sugar. Water is lost to form an acetal/ketal
OCH2OH
HH
OHH
OH
OH
HH
OH
CH3 O H
OCH2OH
HH
OHH
OH
OH
HH
O CH3
+ + H2O
Acetal link: R-O-C-O-R
Acetalcarbon
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7P1-30
Important Monosaccharides
OCH2
HH
OHH
OH
OH
H OH
HOH
OCH2
H
H
OH
H
OH
OH
H OH
HOH
O
H
CH2
H
OH
OH
HCH2OH
OHOH
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7P1-31
Amino Sugars
OCH2
HH
OHH
OH
NH3+
H OH
HOH
-D-glucosamine
OCH2
HH
OHH
OH
NH
H OH
HOH
C OCH3N-acetyl--D-glucosamine
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7P1-32
Amino Sugars-2
NHCO
CH3O
R
OHOH
OH
COO-
CH OHCH OHCH2OH
N-acetylnuraminic acid sialic acid
R=