Strucural elucidaion lactose

chemistry of natural products

1. STRUCTURAL ELUCIDATION OF LACTOSE Presented by; M Pharm (Pharmaceutical Chemistry) students Gunturu .Aparna Akshintala. Sree Gayatri Thota. Madhu latha Kamre. Sunil Daram. Sekhar University college of pharmaceutical sciences Department of pharmaceutical chemistry Acharya Nagarjuna University Guntur 1

2. STRUCTURAL ELUCIDATION OF LACTOSE

3. Lactose occures in mammalian milk, e.g.,cow’s milk contains 4 to 6 % and human milk conains 5 to 8% of this sugar. Lactose molecular formula is C 12 H 22 O 11 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.

4. On acidic or enzymatic (lactase) hydrolysis lactose gives equimolar amounts of glucose and galactose.

5. 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. Lactose

6. When lactose is methylated, it yields methyl heptamethyl lactose which, on vigorous hydrolysis, yields 2,3,6-tri-o-mehyl-D-glucose and 2,3,4,6-tetra-O-methyl-D-galactose. The formation of these products reveals that glucose is the reducing half.

7. 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-methyl-D-galactose.

8. 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.

9. 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

10. Conformation structure of lactose.