STRUCTURAL ELUCIDATION OF LACTOSE
M Pharm (Pharmaceutical Chemistry) students
Akshintala. Sree Gayatri
Thota. Madhu latha
University college of pharmaceutical sciences
Department of pharmaceutical chemistry
Acharya Nagarjuna University
Lactose occures in mammalian milk, e.g.,cow’s milk
contains 4 to 6 % and human milk conains 5 to 8% of
Lactose molecular formula is C12H22O11
Lactose reduces on fehling’s solution, Tollen’s
solution and benedict’s solution, it forms an osazone
and exhibits mutarotation. Therfore, lactose must
possess at least one carbonyl group which is not
involved in he disaccharide linkage.
On acidic or enzymatic (lactase) hydrolysis lactose gives
equimolar amounts of glucose and galactose.
Since lactose is hydrolysed only by lactase(identical
with emulisin) the two monosaccharide units are
linked through beta –glycosidic linkage. This is also
indicated by its low specific rotation.
When lactose is methylated, it yields methyl
heptamethyl lactose which, on vigorous
hydrolysis, yields 2,3,6-tri-o-mehyl-D-glucose and
The formation of these products reveals that
glucose is the reducing half.
When lactose is oxidised by bromine water, it yields
lactobionic acid which, on methylation and hydrolysis yields
2,3,5,6-tetra-O-methyl-D-gluconic acid and 2,3,6-tetra-O-
The formation of these products reveals that in lactose
C-1 of glucose is linked to C-4 of galactose.
This further reveals that glucose is a reducing part and
D-galactose in non-reducing part in lactose.
The point of linkage (C-4) of galactose unit is further
confirmed by osazone formation.
When lactosazone is subjected to acid
hydrolysis, it yields D-galactose and D-glucosazone.
This reaction show that in lactose it is the glucose
unit which possesses a reducing group