Dr.ehab principle carbohydrates
-
Upload
mansoura-university -
Category
Education
-
view
658 -
download
4
Transcript of Dr.ehab principle carbohydrates
![Page 1: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/1.jpg)
Carbohydrates
Polyhydroxy compounds (poly-alcohols) that contain a carbonyl (C=O) groupElemental composition Cx(H2O)y
About 80% of human caloric intake>90% dry matter of plantsFunctional properties
– Sweetness– Chemical reactivity– Polymer functionality
![Page 2: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/2.jpg)
Types of Carbohydrates
![Page 3: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/3.jpg)
Monosaccharides
Monosaccharides are categorized by the number of carbons (typically 3-8) and whether an aldehyde or ketoneMost abundant monosaccharides are hexoses (6 carbons)Most monosaccharides are aldehydes, i.e. aldoses
C
C
OH
H OH
C
C O
H
H OH
aldehyde ketone
![Page 4: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/4.jpg)
Fisher projections
OHH
OHH
OHH
HHO
C
C
C
C
C
C H 2OH
HO
OHH
OHH
O
HHO
C
C
C
C
C H OH2
C H OH21
2
3
4
5
6
D-glucose(an aldohexose)
D-fructose(an ketohexose)
1
2
3
4
5
6
![Page 5: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/5.jpg)
![Page 6: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/6.jpg)
![Page 7: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/7.jpg)
Cyclic Forms
Lowest energy state
HC
C C
OCC
OH
HO
OHHO
H
HH
CH2OHH
123
4 5
6β-D-glucopyranose (glucose)—an aldose
a hexosean aldohexose
—C1 chair conformation
β-D-fructopyranose (fructose)—a ketose
a hexulosea ketohexose
—1C chair conformation
C CO
CCH
H
COH
H
OHH
OHOH
CH2OH1
2
345
6H
![Page 8: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/8.jpg)
Ring Nomenclature
pyranose is a six-membered ring (a very stable form due to optimal bond angles)furanose is a five-membered ring
![Page 9: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/9.jpg)
Chirality
Geometric property of a rigid object (or spatial arrangement of atoms) of being non-super-imposable on its mirror image
OHHOHH
OHHHHO
CCCCCC
its mirror image is an "optical
isomer"H2OH
HO 4 chiral centerse.g. at C2 carbon: This
structure has a non-superimposable mirror imageCHO
(CHOH)3CH2OH
OHHC2
![Page 10: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/10.jpg)
Isomers
Isomers are molecules that have the same chemical formula but different structuresStereoisomer differs in the 3-D orientation of atomsDiastereomers are isomers with > 1 chiral center.
– Pairs of isomers that have opposite configurations at one or more of the chiral centers but that are not mirror images of each other.
Epimers are a special type of diastereomer. – Stereoisomers with more than one chiral center which differ in
chirality at only one chiral center. – A chemical reaction which causes a change in chirality at one
one of many chiral center is called an epimerisation.
![Page 11: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/11.jpg)
Enantiomers
Isomerism in which two isomers are mirror images of each other. (D vs L)
![Page 12: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/12.jpg)
![Page 13: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/13.jpg)
Anomer
An anomer is one of a special pair of diastereomeric aldoses or ketoses – differ only in configuration about the carbonyl carbon
(C1 for aldoses and C2 for ketoses)
![Page 14: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/14.jpg)
Carbonyl Group
Carbonyl groups subject to nucleophilic attack, since carbonyl carbon is electron deficient:– -OH groups on the same molecule act as
nucleophile, add to carbonyl carbon to recreate ring form
![Page 15: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/15.jpg)
OH
HO
OH O
HO
H
OHO
O5
5
5
5 1
11
1
α anomer β anomer
Carbonyl carbon freely rotates→O can attack either side
![Page 16: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/16.jpg)
Specification of Conformation, chiralityand anomeric form of sugars
Determination of chair conformation– Locate the anomeric carbon atom and determine if numbering
sequence is clockwise (n= +ve) or counterclockwise (n= -ve).– Observe if the puckered ring oxygen atom lies “above” (p= +ve)
the plane of the ring or below (p= -ve).– Multiply n*p. If the product is +ve then C1, -ve then 1C
Determination of chiral family– Locate the reference carbon atom contained within the ring and
determine whether the bulky substituent (OH or CH2OH) is equatorial (r= +ve) or axial (r= -ve).
– Multiply n*p*r. If product is +ve the chiral family is D, when it is –ve the chiral family is L
![Page 17: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/17.jpg)
Determination of Anomeric form:– Determine if the hydroxyl substituent on the anomeric carbon atom is
equatorial (a= +ve) or axial (a= -ve).– Multi[ly (n*p) by (n*p*r) by a. When the product is positive, the anomer
is β; when the product is negative the anomer is α
Specification of Conformation, chiralityand anomeric form of sugars
![Page 18: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/18.jpg)
Mutarotation
The α- and β- anomers of carbohydrates are typically stable solids.In solution, a single molecule can interchange between
– straight and ring form– different ring sizes– α and β anomeric isomers
Process is – dynamic equilibrium– due to reversibility of reaction
All isomers can potentially exist in solution– energy/stability of different forms vary
![Page 19: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/19.jpg)
Mutarotation : interconversion of α-and β- anomers
For example, in aqueous solution, glucose exists as a mixture of 36% α - and 64% β - (>99% of the pyranoseforms exist in solution).
![Page 20: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/20.jpg)
Anomer Interconverision
0
10
20
30
40
50
60
70
80
% o
f all
isom
ers
D-glucose D-fructose D-mannose D-galactose
α-pyranoseβ-pyranoseα -furanoseβ-furanose
Generally only a few isomers predominate
![Page 21: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/21.jpg)
TIME
+57.2o
+112o
+19o
pure α-D-(+)-glucopyranose1
pure β-D-(+)-glucopyranose2
[α]D
66% β34% α
(min)
![Page 22: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/22.jpg)
![Page 23: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/23.jpg)
OHHO OH
O
OHO
HO
OHOH
OHO
OH OHOH
H
C
OH
OHH
OHH
CH2OH
OH
HO OH
O
OHOH
H OH
OHH
OHH
CH2OH
HO OH
O H
Mutarotation of ribose
hydrate (0.09%)
keto-form (0.04%)
α-pyranose (20.2%)α-furanose (7.4%)
β-pyranose (59.1%) β-furanose (13.2%)
![Page 24: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/24.jpg)
Stability of Hemiacetals/Hemiketals
As general rule the most stable ring conformation is that in which all or most of the bulky groups are equatorial to the axis of the ring
![Page 25: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/25.jpg)
Reactions
Isomerizationglucose fructose mannose
OxidationR-CHO R-COOHR-CH2OH R-COOH
Reductionsugar sugar alcohols
Acetal formationsugar glycoside
Browning reactions
OCCCCCC
HOH
OHH2OH
OH
OH
HH
H
H
carbonyl group is key
![Page 26: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/26.jpg)
Isomerization
Isomerization is possible because of the “acidity” of the α hydrogen
OCCCCCC
HOH
OHH2OH
OH
OH
HH
H
Hα hydrogen
(on C nextto carbonyl)
OCCCCCC
HO
OHH2OH
OH
OH
HH
H
HO
CCCCCC
HO
OHH2OH
OH
OH
HH
H
Hbase
keto form enol form
![Page 27: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/27.jpg)
Isomerization
OCCCCCC
HOOH
OHH2OH
OH
H
HH
H
HO
CCCCCC
HOHO
OHH2OH
OH
H
HH
H
H CCCCCC
HOO
OHH2OH
OHHH
H
H2OH
D-glucose D-mannose D-fructose
![Page 28: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/28.jpg)
Oxidation/Reduction
OxidationIncrease oxygen or decrease hydrogen
Increase oxidation stateRemove electrons
ReductionDecrease oxygen or increase hydrogen
Decrease oxidation stateAdd electrons
![Page 29: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/29.jpg)
Oxidation
Carbonyl group can be oxidized to form carboxylic acidForms “-onic acid” (e.g. gluconic acid)Can not form hemiacetalVery hydrophillic– Ca gluconate
Can react to form intramolecular esters:– lactones
![Page 30: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/30.jpg)
Oxidation
Also possible to oxidize alcohols to carboxylic acids– “-uronic acids”
Galacturonic acidsPectin
Reactivity– Aldehydes are more reactive than ketones
In presence of base ketones will isomerizeAllows ketones to oxidize
![Page 31: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/31.jpg)
Reducing sugars
Reducing sugars are carbohydrates that can reduce oxidizing agentsSugars which form open chain structures with free carbonyl groupReduction of metal ions– Fehling test: CuSO4 in alkaline solution
![Page 32: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/32.jpg)
DNSA assay
• Colorimetric analysis: the sugars present reduce 3,5-dinitrosalicylic acid, DNSA, to 3-amino-5-nitrosalicylic acid
![Page 33: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/33.jpg)
Reduction
Carbonyl group can be reduced to form alcohol– hydrogenation reaction
Forms sugar alcohol (“-itol”)– glucose glucitol (aka sorbitol)– mannose mannitol– xylose xylitol
Sweet, same calories as sugar, non-cariogenicVery hydrophillicGood humectants
![Page 34: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/34.jpg)
Acetal Formation
In acid solution, sugars can react with alcohols to form acetals known as glycosides
Reaction is a nucleophilic addition of two alcohols to aldehydes
CH2OH
+ ROH
OH
+ H2OH+
O
CH2OH
OR
O
![Page 35: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/35.jpg)
1. Protonation of OH group
2. water removal to form carbocation
3. alcohol addition and release of proton
Acetal Formation
![Page 36: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/36.jpg)
Sucrose Maltose
Trehalose Cellobiose
![Page 37: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/37.jpg)
![Page 38: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/38.jpg)
![Page 39: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/39.jpg)
Stability of acetals
Pyranose >>>> Furanoseβ -glycosidic > α-glycosidic1,6>1,4>1,3>1,2
Allow to predict stability of glycosidic linkages in terms of their resistance to hydrolysis– Gentiobiose
![Page 40: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/40.jpg)
Acid catalyzed Rxns
Acid hydrolysis of hemiactals and hemiketals(mutarotation)Anhydro sugars
– 1C conformationReversion sugars
– Formation of oligosaccharides under conditions of high sugar concentration, dilute acid……. Maple syrup, fruit juice concentrates
– Detection of invert sugar in juices/honeyEnolization and Dehydration
– Formation of 3-deoxyosones and HMF/furfural
![Page 41: Dr.ehab principle carbohydrates](https://reader034.fdocuments.net/reader034/viewer/2022052310/55500cb9b4c90535638b47b3/html5/thumbnails/41.jpg)
Hydrolysis of hemiactals and hemiketals(mutarotation)– Base catalyzed loss of H from anomeric –OH
Acetals and Ketals are stable– Sugar esters will be hydrolyzed in alkali
Enolization– Favored by alkali
Reduction of metal ions– Alkali prevents hydrolysis of non-reducing sugar
Base catalyzed Rxns