Building Blocks of Life
Most Important Chemical
Consideration of Sugars
Consider the anomeric carbon! The aldehyde on the one
position can be nucleophilically attacked by any of the hydroxyls!
Hemiacetalization Concept Key to
Carbohydrate Ring Structures
Nomenclature of Carbohydrates
• D, L Defines the configuration at C5
D has the OH at Right in Fischer projection
L has the OH at Left in Fischer projection
• Gluco defines the configuration of the OH at C2, C4, C5. These OH’s
are on same side while the C3-OH is opposite to others
• α,β defines the configuration of the OH at C1, the anomeric carbon
• Pyran indicates 6 member ring size
• Furan indicates 5 member ring size
Examples follow
In Glucuronic acid C2, C4, C5 OH’s are
on same side
H
C
H
HO
H
H
H
O
OH
C
H
O
OH
H
HO
H
OH
HO
H
OH
H
CO2H
glucuronic acid
OH
CO2H
galacturonic acid
Alditols
• In Mannitol C2, C4,
C5 OH’s are not at
same side in Fisher
Projection
CH2OH
CH2OH
HO
HO
H
H
H
OH
H
OH
H
OH
HO
H
H
OH
CH2OH
CH2OH
Mannitol
Xylitol
Conformations
Anomers
CH2OH
O OH
OH
OH
OH
OH
-D glucopyranose
[a] 25
D
+19o
CH2OH
O
OH
OH
OH
-D glucopyranose
+112o
Rotations of
Fresh
Solutions
25
o
[a]
For aged solutions
=
+52.7
D
Reason: Mutarotation is the best evidence for the cyclic
hemiacetal structure of D-(+)-glucose
Monosaccharides,Hemiacetal Formation II
CH2OH
H
C
C
H
OH
HO
CH2OH
O
..
H
H
C
C
C
H
OH
O
H
H
C
C
H
OH
H
C
C
H
OH
HO
O
OH
C
H
C5 OH attacks aldehyde giving a pyranose ring (6 member structure)
CH2OH
C H O
..
C
H
OH
HO
CH2OH
H
H
HO
C
C
C
H
OH
H
O
H
C H O
C
OH
C
OH
H
C
C
H
OH
H
C4 OH attacks aldehyde giving a furanose ring (5 member structure)
-D glucofuranose
CH2OH
HO
O
OH
-D glucopyranose
Mutarotation
CH2OH
O
OH
OH
OH
OH
Ring closure between
OH C1 and C4 -OH
CHO
OH
CH2OH
OH
OH
CHO
OH
OH
CH2OH
O OH
HO
OH
H
HO
H
H
OH
H
OH
OH
CH2OH
D glucose
CH2OH
OH
CHO
OH
OH
OH
Ring closure between
C1 and C5 -OH
CH2OH
O OH
OH
OH
OH
-D glucofuranose
OH
-D glucopyranose
Hemiacetalization Concept Key to
Carbohydrate Ring Structures
• Oligosaccharides
– consist of several monosaccharide residues
joined together with glycosidic linkages
– di, tri, tetrasaccharides
(depending on the number of monosaccharides)
– up to 10 - 20 monosaccharides (depending on
analytical techniques i.e GC vs LC/MS)
• Polysaccharides
– refer to polymers composed of a large number of
monosaccharides linked by glycosidic linkages
ex. Cellulose
Cellobiose
CH2OH
HO
HO
O
OH
CH2OH
OH
HO
O
O
CH2OH
anhydroglucopyranose
unit
O
HO
O
OH
OH
HO
O
OH
O
CH2OH
n = 1 -5000
oxygen bridge
(ether-type or
glycosidic bond)
Cellulose
-D-anhydroglucopyranose units linked by
(1,4)-glycosidic bonds
6
HO
HO
OH
CH2OH
O
Non-Reducing
End-Group
CH2OH
4
O
HO
5
3
HO
O
2
OH
OH
3'
O
1
4'
5'
2'
CH2OH O
6'
CH2OH
1'
O
O
HO
n
OH
OH
Reducing
End-Group
(potential aldehyde)
Polysaccharides
Polysaccharides are polymers composed of
many monosaccharide units linked by
glycosidic bonds
The glycosidic bond can can have either the α
or a β-configuration and be joined to any of
the hydroxyl groups at C-2, C-3, C-4 or C-6
The chain can either be Linear or Branched
– branches can be single monosaccharide units,
chains of two or more units, or chains of a
variable number of units
Polysaccharides
Polysaccharides can be divided into two classes
– Homopolysaccharides
• consist of only one kind of monosaccharide
ex cellulose
– Heteropolysaccharides
• consist of two or more kinds of
monosaccharides
ex galactoglucomannans
Homopolysaccharides
Homopolysaccharides can be further divided by
the type(s) of glycosidic linkages
Homolinkages - either an α or a β
configuration to a single position (exclusive of
any branch linkages)
•that is a single kind of monosaccharide
linked by one type of bond α-14, β-14,
and so on
Heterolinkages - a mixture of a- and bconfigurations and/or mixture of positions
•usually have a definite pattern for the
arrangement of the linkages
Heteropolysaccharides
Heteropolysaccharides can have the same kind
of linkage diversity as with
homopolysaccharides, but now associated with
one or more of the different kinds of
monosaccharide units
– infinite degree of diversity of structure
Polysaccharides
Polysaccharides can not only have
different sequences of monosaccharide
units, but also different sequences of
glycosidic linkages and different kinds of
branching
– a very high degree of diversity for
polysaccharides and their structurefunction relationships
Plant Polysaccharides
The conformation of individual
monosaccharide residues in a polysaccharide
is relatively fixed, however, joined by
glycosidic linkages, they can rotate to give
different chain conformations.
1,4 glycosidic
linkage
OH
O
HO
O
HO


O
HO
OH
O
1,6 glycosidic
linkage
O
HO
HO

HO
O
HO
OH
HO
HO
O

O
HO
O
Plant Polysaccharides
The different kinds of primary structures that
result in secondary and tertiary structures give
different kinds of properties
– water solubility, aggregation and crystallization,
viscosity, gelation, etc.
Polysaccharides have a variety of functions
– Storage of chemical energy in photosynthesis
– Inducing Structural Integrity in plant cell walls
Starch
Starch is composed completely of D-glucose
– found in the leaves, stems, roots, seeds etc
in higher plants
– stores the chemical energy produced by
photosynthesis
Most starches are composed of two types of
polysaccharides - amylose and amylopectin
– amylose - a mixture of linear
polysaccharides of D-glucose units linked
-(1-4) to each other
• between 250-5,000 glucose residues
The Components of Starch
O
HO
OH
O
OH
O
HO
OH
O
OH
O
(1-4)
HO
Amylose
OH
HO
O
O
OH
HO
O
OH
O
Amylopectin
– Amylopectin - a mixture of branched polysaccharides of Dglucose units linked -(1-4), with ~ 5% -(1-6) branch
linkages
• between 10,000-100,000 glucose residues
OH O
OHO
OH O
HO
OH O
OH
O
OH O
OH O HO
O HO
OHO
HO
(1-4)
OH
O (1-6)
O
OH
O
HO
OH
O
HO
O
Starch Polymer Components
Amylose
Amylopectin (1 residue in every 20 is 16 linked to branch off)
The Components of Starch
Amylose
O
HO
Amylopectin
OH
O
OH O
OH
O
HO
OHO
OH
O
OH O
OH O HO
OH
O
(1-4)
HO
OH
HO
O
O HO
OHO
HO
(1-4)
OH
O (1-6)
O
OH
O
HO
OH
O
O
OH
HO
O
OH O
HO
OH O
OH
O
HO
O
OH
O
Starch tertiary structure (Helix)
Composition of Softwoods and
Hardwoods
Cellulose
42±2%
Cellulose
45 ± 2%
Hemicelluloses
27 ± 2%
Lignin
28 ± 3%
Extractives 3 ± 2%
Hemicelluloses
30 ± 5%
Lignin
20 ± 4%
Extractives 5 ± 3%
Softwood
Hardwood