Chemically, it can be called 4-O-a-D-glucopyranosyl-D-glucopyranose.
Cellobiose is also composed of two units of glucose, but the 1,4
0 - link is
b, instead of a. Thus, it can be called 4-O-b-D-glucopyranosyl-D-glucopyranose. ‘Linkage’ always refers to ‘left-hand’ sugar. For example, in
maltose, since the ‘linkage’ is a, and is in between C-1 of one glucose and
C-4 of the other, the ‘linkage’ is called a 1,4
0 .
Both maltose and cellobiose exist as a and b anomers, and undergo
mutarotation. These are reducing sugars. They react with Benedict’s and
Fehling’s reagents, and also react with phenylhydrazine to yield the
characteristic phenylosazone. If you have a closer look at the following
structures of maltose and cellobiose, you will see that the left-hand glucose
possesses an acetal link (glycosidic link) but the right-hand glucose still has
the hemiacetal at C-1
0 . The right-hand glucose can exist in an equilibrium of
a and b anomers, and the open chain form. This is why maltose and
cellobiose behave like glucose in chemical reactions.
O
O
H
O
O
H
OH
O
O
H
O
H
O
H
OH
OH
O
O
H
O
O
H
OH
OH
O
O
H
O
H
O
H
OH
1
4'
α Link
Maltose
β Anomer
1'
Acetal
Hemiacetal
β Link
Cellobiose
β Anomer
Acetal
Hemiacetal
4'
1'
1
Maltose is hydrolyzed by the enzyme maltase (specific for a-glycosidic
linkage) to two units of glucose, but for the hydrolysis of cellobiose the
enzyme emulsin (specific for b-glycosidic linkage) is necessary. While
maltose is the building block of the polysaccharide starch, cellobiose is the
building block of another polysaccharide, cellulose.
Malt consists of the grain of barley, Hordeum distichon (family Gramineae), partially germinated and dried. Maltose is the major carbohydrate of
malt and malt extracts. Pharmaceutically, extract of malt is used as a vehicle
for the administration of cod-liver oil, and the liquid extract is given with
haemoglobin, extract of cascara and various salts.
Lactose
Lactose, found in milk and a major component of whey, is a disaccharide
that is composed of a unit of glucose and a unit of galactose through a
312
CH6 NATURAL PRODUCT CHEMISTRY
Cellobiose is also composed of two units of glucose, but the 1,4
0 - link is
b, instead of a. Thus, it can be called 4-O-b-D-glucopyranosyl-D-glucopyranose. ‘Linkage’ always refers to ‘left-hand’ sugar. For example, in
maltose, since the ‘linkage’ is a, and is in between C-1 of one glucose and
C-4 of the other, the ‘linkage’ is called a 1,4
0 .
Both maltose and cellobiose exist as a and b anomers, and undergo
mutarotation. These are reducing sugars. They react with Benedict’s and
Fehling’s reagents, and also react with phenylhydrazine to yield the
characteristic phenylosazone. If you have a closer look at the following
structures of maltose and cellobiose, you will see that the left-hand glucose
possesses an acetal link (glycosidic link) but the right-hand glucose still has
the hemiacetal at C-1
0 . The right-hand glucose can exist in an equilibrium of
a and b anomers, and the open chain form. This is why maltose and
cellobiose behave like glucose in chemical reactions.
O
O
H
O
O
H
OH
O
O
H
O
H
O
H
OH
OH
O
O
H
O
O
H
OH
OH
O
O
H
O
H
O
H
OH
1
4'
α Link
Maltose
β Anomer
1'
Acetal
Hemiacetal
β Link
Cellobiose
β Anomer
Acetal
Hemiacetal
4'
1'
1
Maltose is hydrolyzed by the enzyme maltase (specific for a-glycosidic
linkage) to two units of glucose, but for the hydrolysis of cellobiose the
enzyme emulsin (specific for b-glycosidic linkage) is necessary. While
maltose is the building block of the polysaccharide starch, cellobiose is the
building block of another polysaccharide, cellulose.
Malt consists of the grain of barley, Hordeum distichon (family Gramineae), partially germinated and dried. Maltose is the major carbohydrate of
malt and malt extracts. Pharmaceutically, extract of malt is used as a vehicle
for the administration of cod-liver oil, and the liquid extract is given with
haemoglobin, extract of cascara and various salts.
Lactose
Lactose, found in milk and a major component of whey, is a disaccharide
that is composed of a unit of glucose and a unit of galactose through a
312
CH6 NATURAL PRODUCT CHEMISTRY