The document provides information about Ahmed Metwaly's academic positions and areas of research interest which include oligosaccharides, their classification, structure, properties and examples. It then discusses specific oligosaccharides in more detail including reducing and non-reducing disaccharides, their structures, sources and uses. Further sections cover topics such as glycosidic bond formation, enzymatic hydrolysis of glycosides, and potential applications of oligosaccharides.

1. Associate Professor of Pharmacognosy , Faculty of Pharmacy, Al-Azhar University, Cairo, Egypt
•Associate Professor, City of Scientific Research and Technological Applications (SRTA-City), Alexandria,
Egypt
•Senior research fellow, Liaoning University of Traditional Chinese Medicine, China (20118-2019)
•Visiting scholar, School of Pharmacy, University of Mississippi, USA (2012-2014)
Ahmed Metwaly
Oligosaccharides

2. ▪ They are crystalline and soluble in water.
▪ They are hydrolysable by acids or specific enzymes to yield from 2-10 molecules of
monosaccharides.
▪ The monosaccharide units are linked through glycosidic linkages.
▪ They are subclassified on the basis of the number of sugar molecules into di-, tri- or
tetrasaccharides and so on.
▪ The two sugar units are linked through their reducing groups, the resultant disaccharide will be non-
reducing e.g. sucrose (a1 glucose -b 2 fructose). Theoretically, there are four possible forms: a1-a 2, a 1-b 2,
b1-a2, or b1-b2.
▪ The reducing group of the first molecule
e.g. C-1 of an aldose is linked to C-2, C-3,
C-4, or C-6 of another aldose; the
reducing group of the second molecule is
thus free and the resultant disaccharide will
be reducing. The common disaccharides
are linked through C1-C4,

3. The anomeric hydroxyl and a hydroxyl of another sugar or some other compound can join together, splitting out
water to form a glycosidic bond:
R-OH + HO-R' → R-O-R' + H2O
e.g., Methanol reacts with the anomeric OH on glucose to form methyl glucoside (methyl-glucopyranose).
O
H
HO
H
HO
H
OH
OH
H
H
OH
a-D-glucopyranose
O
H
HO
H
HO
H
OCH3
OH
H
H
OH
methyl-a-D-glucopyranose
CH3-OH
+
methanol
H2O

4. ▪ a-glycosides are hydrolyzed by a-glycosidases (e.g. maltase obtained from barley) and
▪ b-glycosides by b-glycosidases (e.g. emulsin obtained from bitter almond).

5. 5
cellobiose:
maltose:
O
OH
HO
HO
OH
O
OH
OH
HO
O
OH
O
OH
OH
HO
O
OH
O
OH
HO
HO
OH
O
CH2OH
HO
OH
HOCH2
O
O
OH
HO
HO
OH
sucrose:
reducing
sugar
reducing
sugar
nonreducing
sugar
Reducing disaccharides
Reducing sugars: free hemiacetal (always in equilibrium with open chain aldehyde)

6. REDUCING DISACCHARIDES
MALTOSE (MALT SUGAR)
▪ Sources: It is the main constituent of malt and germinating cereals.
▪ Structure:
▪ It consists of two glucose units, linked by α1-4. It is hydrolyzed by maltase enzyme (α-glucosidase).
▪ It exists in two anomeric forms α-maltose and β-maltose, which undergo mutarotation.
▪ Properties
▪ It reduces Fehling’s solution but does not reduce Barfoed’s solution.
▪ It forms a characteristic osazone (rosettes of plates or broad needles).
▪ Preparation
▪ Maltose is prepared from starch by partial acid hydrolysis, or by using α -amylase enzyme isolated
from green malt.
▪ Uses: Nutrient.
O
CH2OH
O
O
CH2OH
O
HO
HO
O
OH
OH
O
HO
OH
OH
OH
1 4
1 4
Maltose
4-O-(a-Dglucopyranosyl)-D-glucopyranose
Glu-a1-4-Glu

7. LACTOSE (MILK SUGAR)
▪Sources:
▪ Lactose is the principal sugar of mammalian milk. It is not present in higher plants.
▪Structure:
▪ It consists of galactose and glucose, linked by a b 1— 4 linkage. It is hydrolyzed by
emulsin enzyme.
▪ Properties
▪
It reduces Fehling’s solution but does not reduce Barfoed’s solution.
It forms a characteristic osazone (needles aggregated in clusters or tufts).
▪ Preparation
▪ Lactose is obtained from whey
(a by-product from cheese manufacture)
after concentration, upon which deposits of lactose crystallize out.
▪Uses:
▪ Nutrient in infant food.
▪ Diluents in tablets.
O
O
HO
OH
OH
OH
O
CH2OH
O
OH
HO
OH
OH
O O
CH2OH
Lactose
4-O-b-(D-galactopyranosyl)-D-glucopyranose
Gal-b1-4 Glu
1
4
1
4

8. NON-REDUCING DISACCHARIDES
SUCROSE
O
HO
HO
OH
OH
O
CH2OH
CH2OH
O
CH2OH
O
CH2OH
O
CH2OHO
Sucrose
a-D-glucopyranosyl-b-D-fructofuranose
[Glu-1a-2b-Fru]
2
1
Sources:
Sugar cane.
Sugar beet.
Properties:
It is readily soluble in water.
It has a sweetening power more than glucose and less
than fructose.
▪ It gives positive results with cobalt nitrate test (violet) and
▪ Seliwanoff’s test (rapid furfural).
▪ It does not reduce Fehling’s solution.
▪ It does not form an osazone.
Its solution does not undergo mutarotation
Uses:
Used in syrup preparation, tablet manufacture, nutrient
and demulcent .
Sucrose is also used in preparation of dextran (a
polysaccharide used as plasma substitute)

9. ▪ Invert sugar:
Sucrose is (d, +) with [a]20
d = +66.50. On hydrolysis by dil. acids or by invertase enzyme from yeast, it yields
mixture of (+)d-glucose (+52.50)and (-)d-fructose (-920). Because of high negative rotation of the fructose, the final
sign of the solution [a]20
d of the mixture (- 20.40) is changed from (+) to (-). that is why it is called invert sugar
or inversion.
Uses:
▪Sweetening agent as it is more sweet than sucrose.
▪Adulteration of honey.
▪It can be detected by test for cl-

10. O O
CH2OH
O
HO
HO
O
OH
OH
O
HO
OH
OH
OH
O
CH2OH
1
4
1
4
Cellobiose
4-O-b-(D-glucopyranosyl)-D-glucopyranose
Glu-b1-4 Glu
Gentiobiose:
Composed of two glucose unites linked by b 1— 6 linkage.
Rutinose:
Composed of glucose and rhamnose linked by b 1— 6 linkage.
Cellobiose is two glucose unites linked by b 1— 4 linkage. not found in nature, but
obtained from cellulose by either careful acid hydrolysis or by the action of cellulase
enzyme

11. ▪ Chemical structures
▪ Fibres
▪ Vitamins
▪ Phytoconstituents

12. Composition
Metabolism
Enzymes
Minerals
Phytoconstituents

13. ▪Antimicrobial
▪Antioxidant properties
▪Wounds and burns
▪Respiratory tract
▪GIT
▪Honey and fertility
▪…..

14. ▪ https://www.mdpi.com/2079-6382/8/4/251/htm

16. https://doi.org/10.1016/j.jtv.2015.12.002

18. O
HO
HO
O
OH
CH2
O
O
O
CH2OH
O
OH
HO
OH
OH
O
O
CH2
CH2OH
CH2OHO
CH2OH
CH2OH
O
Raffinose
a-D-galactopyranosyl (1-6)-O-a-Dglucopyranosyl-(1-2) b-D-fructofuranose
Gal a1-6 Glu a-1-2b Fru
1
6
1
2
6
1
1
2
Raffinose (melizitose, melitriose or gossypose)

19. Gentianose
O
HO
HO
O
OH
OH
O
CH2OH
O
O
CH2
O
O
HO
HO
OH
CH2
1
6
6
1
Gentianose
b-Dglucopyranosyl (1-6) -D-glucopyranosyl-(1-2) b-D-fructofuranose
Glu-b1-6-Glua-1-2b Fru
CH2OH
CH2OH
O
2
O
CH2OH
CH2OH
O
2
1
1

20. Oligosaccharides
Disaccharides
Non Reducing
Sucrose
Alpha glucose+
beta fructose
Trehalose
Alpha glucose
Reducing
1,3 linkage
Turanose
1,4 linkage
Maltose
Alpha glucose
Lactose
Beta
galactose+beta
glucose
Cellobiose
Beta glucose
1,6 linkage
Melibiose
Alpha
galactose+alpha
glucose
Gentiobiose
Beta glucose
Trisaccharides
Raffinose Gentianose

22. LACTULOSE
▪ Galactose-b-(1,4)-fructose
▪ A semi-synthetic disaccharide (not naturally occurring)
▪ Not absorbed in the GI tract
▪ Used either as a laxative in constipation and for hepatic encephalopathy
Mechanism
• Lactulose is not absorbed in the small intestine nor broken down by human enzymes, thus
stays in the digestive bolus through most of its course, causing retention of water through
osmosis leading to softer, easier-to-pass stool.
• Fermented by the gut flora, producing metabolites which have osmotic powers and
peristalsis-stimulating effects (such as acetate), but also methane associated with flatulence.
• Lactulose is metabolized in the colon by bacterial flora into lactic acid and acetic acid.
These partially dissociate, acidifying the colonic contents the formation of the nonabsorbable
NH4 from NH3, trapping NH3 in the colon and effectively reducing plasma NH3 concentrations.
(hepatic encephalopathy)
• There have also been studies demonstrating the capacity for lactulose to minimize the
formation of gallstones.
• Anticancer potentiality owing to its ability to bind galactin carbohydrates involved in
various tumor progressions

23. SUCRALFATE (Aluminum salt of sucrose orasulfate)

24. ▪ These are crystalline substances obtained from starch by the action of specific enzymes.
▪ They are differentiated into : a , b and g cyclodextrins with 6, 7 and 8-glucopyranose units respectively.
▪ They are arranged in cylindrical macro-rings with a hydrophobic central cavity (central core) and a
hydrophilic outer surface.
▪ Uses
Cyclodextrins are of great pharmaceutical importance. They are used as “drug enclosures” in order to:
▪ Reduce side effects,
▪ Mask unpleasant taste,
▪ Allow drug stabilization and avoid drug-interaction and
▪ Enhance drug solubilization.