Cyclic monsaccharide structures and anomeric forms
Glucose (an aldose) can cyclize to form a cyclic hemiacetal Fructose (a ketose) can cyclize to form a cyclic hemiketal Cyclic form of glucose is a pyranose Cyclic form of fructose is a furanose
Pairs of isomers that have opposite configurations at one or more chiral centers but are NOT mirror images are diastereomers
Two sugars that differ in configuration at only one chiral center are epimers
Epimers
Epimers are two sugars that differ only in the configuration around one carbon atom of their structures.
D-Mannose differs from D-glucose only in its configuration around carbon 2.
Stereochemistry Review
D,L designation refers to the configuration of the highest-numbered asymmetric center
D,L only refers the stereocenter of interest back to D- and Lglyceraldehyde!
D,L do not specifБайду номын сангаас the sign of rotation of plane-polarized light!
D-sugars predominate in nature
More Stereochemistry
Know these definitions
Stereoisomers that are mirror images of each other are enantiomers
Glucose Galactose Mannose Ribose Arabinose Xylose Fructose
Glucose is the standard six-carbon sugar Galactose is an epimer of glucose Mannose is an epimer of glucose Ribose is the standard five-carbon sugar Arabinose is an epimer of ribose Xylose is an epimer of ribose Fructose is the ketose form of glucose
Haworth Structures – Step 1
1 CHO
H 2 OH
HO 3 H
4
H
OH
H 5 OH
6 CH2OH
6
HOH2C
H
5
H OH H
43 2
1
CHO
OH OH H OH
Haworth Structures – Step 2
H H OH H 1
6
HOH2C
5
4
3
2 CHO
OH OH H OH
simpler sugars under mild conditions Oligo = "a few" - usually 2 to 10 Polysaccharides are polymers of the simple sugars
Monsaccharides
An organic chemistry review Aldoses and ketoses contain aldehyde and ketone functions, respectively Triose, tetrose, etc. denotes number of carbons Aldoses with 3C or more and ketoses with 4C or more are chiral Review Fischer projections and D,L system
1
H OH
2
OH
HOH2C 6
H
5
H
4
OH
OH
3
H
O
OH
1
H
2
H
OH
α-, D-glucose
β, D-glucose
Cyclic monsaccharide structures and anomeric forms
D-Galactose differs from D-glucose only in its configuration around carbon 4.
D-Galactose and D-Mannose are not epimers.
Structures with which to be Familiar
HOH2C 6
H
5
H
4
OH
OH
3
H
OH
H
2
1
CHO
OH
Haworth Structures – Step 3
HOH2C 6
H
5
H
4
OH
OH
3
H
OH
H
2
1
CHO
OH HOH2C 6
H
5
H
4
OH
OH
3
H
O
1
CHOH H
2
OH
α and β enantiomers
HOH2C 6
H
5
H
4
OH
OH
3
H
OH
Carbohydrates
Outline
1. Carbohydrate Nomenclature 2. Monosaccharides 3. Oligosaccharides 4. Polysaccharides
Nomenclature
Carbohydrates are hydrates of carbon Monosaccharides (simple sugars) cannot be broken down into