Reactions of monosaccharides

In this section, we describe Reactions of Monosaccharides and most of the slides are cited from:
1- Lippincott's Illustrated Biochemistry
2- Harper's Biochemistry
3- U Satyrana Biochemistry

1. Reactions of Monosaccharides

Asst. Prof. Dr. Muhammad Haroon
MD, ECEA, MPH (JHSPH)

Lecturer at Kandahar Medical faculty & MPH
Former Biochemistry Guest lecturer at SMS
medical college, India.
Email:[email protected]

2. Introduction

e The following reactions indicate monosaccharide
properties:
- Esterification
- Oxidation
- Reduction
- Dehydration
— Interconversion

Intr. to Carbohydrates

3. Esterification

e The hydroxyl groups of monosaccharides can form
esters with:
- Acids

e Phosphoric esters of monosaccharides are seen:

- Commonly in living organisms

e They are formed by:

- Enzymatic reactions
Intr. to Carbohydrates

4. Esterification Cont..........

ca , O O
R-OH +HO-P-OH —=HO-P-OH + HO
OH O-R

Intr. to Carbohydrates

5. Oxidation

e Oxidation of monosaccharide produce:
- Sugar Acids

e Sugar acids produced are divided into three groups:
- Aldonic Acid
- Aldaric Acid (Glycaric Acid)
- Uronic Acid

Intr. to Carbohydrates

6. Aldonic acid

e Definition:
- Aldehyde group of aldoses is converted to a carboxyl
group
e Oxidizing agents:
— Mild oxidizing agent (Br,+HOH) Hypobromite
e It produces:
- Glucose (Gluconic Acid)
— Mannose (Mannonic Acid)
- Galactose (Galactonic Acid)

Intr. to Carbohydrates

7. Aldonic acid Cont..........

T
Mild
En oxidising H zu 0h
HO—C—H agent HO—C—H
| ——= |
En nu Ju u
de to
CH,OH CH,OH

Intr. to Carbohydrates

8. Aldaric Acids

e Definition:

- Aldehyde group of aldoses & last alcohol groups are both
converted to carboxyl groups

e Oxidizing agents:

— Strong oxidizing agent (Hot HNO3)
e It produces:

- Glucose (Glucaric Acid)

— Mannose (Mannaric Acid)

- Galactose (Galactaric Acid)

Intr. to Carbohydrates

9. Aldaric Acids Cont..........

| COOH

H—C—OH Strong
oxidising H—G—OH
HO—C—H agent HO—C—H
| u
H— 7 — OH H—C— OH
H—C—OH H— $ — OH
CH,OH COOH
Saccharic acid
Glucose

Intr. to Carbohydrates

10. Uronic Acid

e Definition:
- Oxidation of terminal alcohol group of aldoses are
converted to carboxyl group
e Oxidizing agents:
— Specific enzymes in human body
e It produces:
- Glucose (Glucuronic Acid) (Most important)
— Mannose (Mannose Uronic Acid)
- Galactose (Galactose Uronic Acid)

Intr. to Carbohydrates

11. Uronic Acid Cont..........

Intr. to Carbohydrates

12. Glucuronic Acid

e Uses:
- Detoxification a number of harmful substances
- Constituent of several mucopolysaccharides

e How glucuronic acid detoxify:

- Converting water non-soluble substances to water soluble
substances

- In order to eliminate them through kidney

Intr. to Carbohydrates

13. Reduction

e Reaction:

- Monosaccharides are reduced to sugar alcohols

e They are reduced in the presence of:

- Sodium Amalgam $ OH
H——C ———0H H——C—0H

HO—C—H NaBH, HO—C—H
H—C—OH SHOH H—C—0H
H—C——OH H——C——-OH

CH,OH CH¿OH

D.Glucose Sorbitol

Intr. to Carbohydrates

14. Reduction Cont..........

e Important monosaccharides and their corresponding

alcohols:

D-Glucose ——
D-Galactose —>
D-Mannose —>
D-Fructose ——

D-Ribose

—

D-Sorbitol

D-Dulcitol

D-Mannitol

D-Mannitol + D-Sorbitol
D-Ribitol

Intr. to Carbohydrates

15. Sorbitol & Mannitol

e Sorbitol:
- Have strong osmotic property
- Produced to much in Diabetes Mellitus

- Leading to swelling of cells and causes cataract,
peripheral neuropathy, nephropathy

e Mannitol:

- Useful in reducing intracranial pressure by force diuresis

Intr. to Carbohydrates

16. Dehydration

e Monosaccharides are dehydrated by:
- Strong mineral acids e.g. hydrochloric acid and Sulphuric
acid
e In the process they lose:
- Three molecule water
e They are converted into:
- Furfural
- Hydroxy methyl Furfural

Intr. to Carbohydrates

17. Dehydration Cont..........

H-C=0 H-C=0
H-G-0H zu
ee Conc. H2SOy sl 6
sh du ao F7
LE bei ¢
CH20H CH20H

D-Glucose Hydroxymethyl furfural

Intr. to Carbohydrates

18. Interconversion

e D-Glucose is allowed to stand in a dilute alkali for a
few hours:
— It forms both D-Fructose & D-Mannose
e The interconversion occurs via formation of:
- Common Enediol intermediate
e Cause:

- Poor stability of the monosaccharides in alkaline
solutions

Intr. to Carbohydrates

19. Interconversion Cont..........

H
H-6-OH
C=O H-G=0
Ho-d-H HO-C-H
—H À HO-C-H
D-Fructose !
D-Mannose

Intr. to Carbohydrates

20. Derivatives of

Monosaccharides

Intr. to Carbohydrates

21. Introduction

e Many important structural and functional
compounds are derived from monosaccharides:
— Sugar acids (Studied earlier)
— Sugar alcohols (Studied earlier)
— Amine derivatives
- Deoxy sugars (studied earlier)
- Ascorbic acid (Vitamin C)

Intr. to Carbohydrates

22. Amine Derivatives

e Definition:

- In these compounds, Second carbon hydroxyl group of
aldo-hexoses are converted to amine

e It produce:
- Glucose Amine (Present in Hyaluronic acid)
- Galactose Amine (Present in Chondritin Sulphate)
- Mannose Amine ( Present in Sialic acid & Erythromycin)

Intr. to Carbohydrates

23. Amine Derivatives Cont..........

Intr. to Carbohydrates

24. Ascorbic Acid (Vitamin C)

e Water soluble vitamin structure closely resembles:
- Glucose
e It is produced from glucose in:
- Some animals & Primates
- Not in humans
e Humans must obtain it from:
- External source

Intr. to Carbohydrates

25. Diagnostic Reactions of
Monosaccharides

Intr. to Carbohydrates

26. Introduction

e There are many biochemical tests

e The most important are:
- Osazone Test
- Benedict Test

Intr. to Carbohydrates

27. Osazone Test

e Principle:
- The reaction involves the the carbonyl carbon and
adjacent carbon
- One molecule of sugar reacts with phenyl hydrazine and
forms phenyl hydrazone
- Then reacts with two additional molecules of phenyl
hydrazine to form Osazone
e Procedure:

1. To a 5 ml sugar solution add 300 mg phenyl hydrazine

(one or two scoopfuls)
Intr. to Carbohydrates

28. Osazone Test Cont..........

e Procedure Cont.........:
2. To a 5 ml sugar solution add 300 mg phenyl hydrazine
(one or two scoopfuls)
3. Shake well
4. Heat in boiling water (15-45 minutes)
5. Take out and allow cooling at room temperature
6. Avoid cooling by water (It disturbs crystallization)
e Observation:
- Crystals are formed (1-5 minutes)

Intr. to Carbohydrates

29. e Galactose crystals are formed:
- Within 20 minutes

e Glucose, mannose and fructose produce identical
crystals

Intr. to Carbohydrates

30. Osazone Test Cont..........

H-0=0 H—G=N—NH—Cók

H—C—OH H—C—OH
| 7 S I

Ro CHNH-NH, HO _R
Aldose Phenylhydrazone

C¿H¿NH-NH,

C¿H¿NH) + NH,
E BENDER able
TEN NER Celts ZT eo
R H,0 C,gH;NH-NH, R
Osazone Intermediate compound
Intr. to Carbohydrates

31. Benedict Test

e Principle:
- Carbohydrates with free aldehyde or keto reduce metallic
ions
- In this test, cupric ions are reduced
- Cupric hydroxide is reduced to cuprous oxide which
separates out of the solution as a red precipitate
e Benedict’s reagent contain:
- Copper Sulphate
- Sodium citrate

— Sodium carbonate Ts

32. HO H + 204%

Blue

OH solution
OH
CH¿OH
D-Glucose

Negative test

for reducing

sugar

Benedict Test Cont..........

Oxidation of
D-glucose
HO——H + Cu,0
Benedict's Brick-red
reagent, heat au solid
H—}— 0H
CH¿OH
D-Gluconic acid
Positive test
for reducing
sugar
Brick-red precipitate
Cu Cu,0(s) Intr. to Carbohydrates

33. e Procedure:
1.

om qe > a

Benedict Test Cont..........

To 5 ml of benedict’s reagent add exactly 8 drops of
sugar

Mix well

Boil for two minutes (Boiling water bath 3 minutes)
Allow to cool in test tube rack

Don’t cool by immersing in cold water (It can some
times be cooled)

Intr. to Carbohydrates

34. Benedict Test Cont..........

e Observation:
- The entire body of solution will be filled with a
precipitate
- The color varies with concentration from green, yellow,
orange or brick red
e Inference:

- The galactose, glucose, fructose and mannose give
positive result
- Color gives an idea of concentration

Intr. to Carbohydrates

35. Benedict Test Cont..........
COI

Benedict's test for sugars

TT

0-0.5% 0.6-1.0% 1.1-1.5% 1.6-2.5% 2.6-3.5% 3.6-4.0% >4.0%

Intr. to Carbohydrates

36. Benedict Test Cont..........

e Application:
- The presence of glucose, galactose and mannose in urine
e Glucosuria:
- Diabetes Mellitus
- Alimentary & Renal
e Fructosuria:
- Fructokinase deficiency
e Galactosuria:

- Galactokinase deficiency
Intr. to Carbohydrates

37. References

Harvey, Richard A., Ph. D. (2017). Lippincott's illustrated
reviews: Biochemistry. 7' Edition. Philadelphia :Wolters
Kluwer Health,

e Murray, R. K. (2016). Harper's illustrated biochemistry. 31%
Edition. New York: McGraw-Hill.

e The images are retrieved from www.google.com/images

Intr. to Carbohydrates

38. Thank You

Intr. to Carbohydrates