and pulses, is an oligosaccharide composed of three monosaccharide units,
i.e. galactose, glucose and fructose.
Polysaccharides Polysaccharides are composed of a huge number of
monosaccharide units, and the number forming the molecule is often
approximately known. For example, cellulose and starch are polysaccharides composed of hundreds of glucose units.
Classification of monosaccharides according to functional groups and carbon
numbers
The two most common functional groups found in monosaccharides (in
open chain form) are aldehyde and ketone. When a monosaccharide
contains an aldehyde, it is known as an aldose, e.g. glucose, and in the
case of ketone, it is called a ketose or keto sugar, e.g. fructose.
O
H
OH
OH
OH
OH
O
H
O
H
OH
OH
OH
OH
O
1
2
3
4
5
6
D-Glucose, an aldose
Contains an aldehyde group
1
2
3
4
5
6
D-Fructose, a ketose
Contains a ketone group
Depending on the number of carbon atoms present, monosaccharides are
classified as triose, tetrose, pentose or hexose, containing three, four, five or
six carbon atoms, respectively. Glucose is a hexose as it contains six carbon
atoms. Sometimes, monosaccharides are classified more precisely to denote
the functional group as well as the number of carbon atoms. For example,
glucose can be classified as an aldohexose, as it contains six carbon atoms as
well as an aldehyde group.
If any monosaccharide lacks the usual numbers of hydroxyl groups, it is
often called a deoxy sugar. For example, 2-deoxyribose, which is a component
of DNA nucleosides, has one less hydroxyl group than its parent sugar, ribose.
O
H
OH OH
O
H
OH
O
H
OH
O
H
OH
D-Ribose, an aldopentose
A component of RNA nucleosides
D-2-Deoxyribose, a deoxy aldopentose
A component of DNA nucleosides
Hydroxyls, aldehyde and keto groups are not the only functional groups
that are present in monosaccharides. Monosaccharides containing carboxylic acid (–COOH) and amino (–NH 2 ) groups are common structural
units in biologically important carbohydrates. For example, 2-amino-2deoxy-D-glucose, also known as glucosamine, is an amino sugar, and
glucuronic acid is a sugar acid.
304
CH6 NATURAL PRODUCT CHEMISTRY
i.e. galactose, glucose and fructose.
Polysaccharides Polysaccharides are composed of a huge number of
monosaccharide units, and the number forming the molecule is often
approximately known. For example, cellulose and starch are polysaccharides composed of hundreds of glucose units.
Classification of monosaccharides according to functional groups and carbon
numbers
The two most common functional groups found in monosaccharides (in
open chain form) are aldehyde and ketone. When a monosaccharide
contains an aldehyde, it is known as an aldose, e.g. glucose, and in the
case of ketone, it is called a ketose or keto sugar, e.g. fructose.
O
H
OH
OH
OH
OH
O
H
O
H
OH
OH
OH
OH
O
1
2
3
4
5
6
D-Glucose, an aldose
Contains an aldehyde group
1
2
3
4
5
6
D-Fructose, a ketose
Contains a ketone group
Depending on the number of carbon atoms present, monosaccharides are
classified as triose, tetrose, pentose or hexose, containing three, four, five or
six carbon atoms, respectively. Glucose is a hexose as it contains six carbon
atoms. Sometimes, monosaccharides are classified more precisely to denote
the functional group as well as the number of carbon atoms. For example,
glucose can be classified as an aldohexose, as it contains six carbon atoms as
well as an aldehyde group.
If any monosaccharide lacks the usual numbers of hydroxyl groups, it is
often called a deoxy sugar. For example, 2-deoxyribose, which is a component
of DNA nucleosides, has one less hydroxyl group than its parent sugar, ribose.
O
H
OH OH
O
H
OH
O
H
OH
O
H
OH
D-Ribose, an aldopentose
A component of RNA nucleosides
D-2-Deoxyribose, a deoxy aldopentose
A component of DNA nucleosides
Hydroxyls, aldehyde and keto groups are not the only functional groups
that are present in monosaccharides. Monosaccharides containing carboxylic acid (–COOH) and amino (–NH 2 ) groups are common structural
units in biologically important carbohydrates. For example, 2-amino-2deoxy-D-glucose, also known as glucosamine, is an amino sugar, and
glucuronic acid is a sugar acid.
304
CH6 NATURAL PRODUCT CHEMISTRY