Dr. Ashraf Taha Khalil. Carbohydrates Definition Organic compounds composed of C, H and O with H and...

Dr. Ashraf Taha Khalil

Carbohydrates

Definition•Organic compounds composed of C, H and

O with H and O present in the same ratio as in water. e.g. Glucose C6H12O6. Simple sugars end with suffix “ose”

•Naturally occurring compounds, consisting of carbon, hydrogen, and oxygen, whose primary function in the body is to supply energy.

•Exceptions:–-Deoxy sugars such as Rhamnose C6H12O5, digitoxose C6H12O4

–-Some non carbohydrates follow the definition:» Acetic acid C2H4O2

» Formaldehyde HCHO»Lactic acid C3H6O3

•New definition:Optically active Polyhydroxy aldehydes or ketones, or substances that hydrolyze to yield polyhydroxy aldehydes or ketones .

Carbohydrates

Sugars (Saccharides) Polysaccharidesmore than 10 sugar units

Monosaccharides Disaccharides Oligosaccharides3- 10 units

Triose: Glyceraldehyde

Tetroses: Erythrose

Pentoses: Arabinose, xyloseHexoses

AldohexeosesGlucose

KetohexeosesFructose

ReducingLactoseMaltoseCellobiose

Non-ReducingSucroseTrehalose

Trisaccharides RaffinoseTetrasaccharides

Pentasaccharides

Homopolysaccharides Heteropolysacchaides

Stachyose

Gums, Mucilage, Pectin,Agar, Heparin, Alginate

Hexosans Pentosans

Starch, Glycogen, InulinCellulose, Dextrin

Glucosans Fructosans

XylansGalactoseMannoseAllose

Physical Characters

•Condition: Sugars are white, crystalline in shape and with sharp melting points, while polysaccharides are white amorphous solids.

•Taste: Sugars have a sweet taste (to various degrees) Polysaccharides are tasteless.

•Solubility: Monosaccharides are soluble in cold water and hot alcohol. Polysaccharides are partially soluble in hot water.

Oscillating Oscillating electricelectric and and magnetic magnetic fields of a beam of ordinary lightfields of a beam of ordinary light

•Optical activity: •A compound is optically active when, in solution, it is capable of rotating

the plane of polarized light either to right (dextrorotatory, + or d) or to the left (levorotatory, - or l).

•The optical activity of a compound is measured by determination of its specific optical rotation ([] D

t) using a polarimeter, and applying the following equation :

][D25 = /LC

Where: = extension of rotation , L = length of tube (light path) in decimeter ,

C = concentration g /ml , 25 = operating temperature (t) in 0C

D = line spectrum of sodium light (589 nm).

Plane polarized lightNichol prism

Normal light

Sugar sample AnalyserSugar sample

Sugar isomers:

•-Hexoses, like glucose, have 4 asymmetric (chiral) carbons (n = 4), each attached to 4 different groups

•-Number of isomers can be calculated from the formula:

Number of isomers = 2n

= 24 =16

D-glucose

D and L in sugars (configuration):•A monosaccharide in which the OH group attached to the

carbon atom next to the CH2OH (farthest asymmetric carbon atom from the carbonyl group) is always to the right is designated as a “D-sugar” and that with the same OH to the left as “L -sugar”. They are non-superiomposable mirror images

•)enantiomers(•D and L designations are like (R) and (S) designations in that

they are not related to the optical rotations of the sugars to which they are applied. Thus, one may encounter sugars that

are D (+) or D (-) and others that are L (-) or L.(+)

D-Glyceraldehyde L-Glyceraldehyde

L-series..………D-series ...……

»Glucose and Fructose have the same molecular formula C6H12O6. They have different structures with different functional groups (different connectivity). They are

described as “Structural Isomers.”

D-Glucose D-Fructose

D-glucose L-glucose D-allose D-mannose

D-glucose D-mannose D-glucose D-galactose

enantiomers Diastereoisomers

epimers 4-epimers

Isomerism in sugarsIsomerism in sugars (Richstein formula)

Terms used to describe isomerism:

•Glucose and Galactose are different from each other in the stereochemistry of carbon 4. They are described as “4-

Epimers.”•Glucose and Mannose are different from each other in the

stereochemistry of carbon 2. They are described as “Epimers”(also diastereoisomers)

D- Mannose

Epimers:

D-Glucose

D-Galactose

D-Glucose

Galactose and Mannose are different from each other in the stereochemistry of carbons 2 and 4. They are described as “Diastereoisomers”. They are not mirror images and differ widely in both physical and chemical properties.(2,4-epimers)“Epimers” are diastereoisomers which differ in configuration of single asymmetric center adjacent to anomeric one (C=O)

e.g. Glucose & mannose (Plate #12)

D-Galactose

D- Mannose

D-Glucose

Typical epimers2,4-epimers

- and - anomers of glucose:

•-When sugars undergo cyclization C-1 became a new chiral carbon and two isomers exist. They are called “ Anomers .”

•-In the -anomer the OH group is directed downside and in the -anomer is directed to the upper side .

•-These two forms have different specific rotation, in solution an equlibrium exsit between the two forms (mutarotation

phenomenon) .

Haworth formulationsChair forms, pyranose structure

-D-glucopyranoside-D-glucopyranoside -D-glucopyranoside

-D-glucopyranoside

anomericproton

-L-glucose -D-glucose -D-glucose -L-glucose

OHOH2C

OH D-glucopyranose D-glucopyranose

Cyclic structure of glucose

Fischer formula

Chair, pyranose structure

Linear & cyclic structuresLeft (OH) upwards

Right (OH) downwards

D-series: (farthest OH is directed to right direction, downwards)

anomeric OH

L-Series: (farthest OH is directed to left direction, upwards)

Anomeric OH

-D glucose

•MutarotationWhen a sugar is dissolved in water, the specific rotation of the solution gradually changes until it reaches a constant value due to equilibrium between and forms (form is more positive value)

e.g. freshly prepared solution of -glucose has a specific rotation +112o. When this solution is allowed to stand the rotation falls till reach + 52.7o.

The equilibrium reached is:

36% –D- glucose []D = + 18.7 0

64% –D- glucose []D = + 112 0

The mean is + 52.7 o

Proof of Cyclic Structure Of Proof of Cyclic Structure Of GlucoseGlucose::

•1 (Infra-red spectra of glucose solution showed no C=O absorption band (around 1700 cm-1)

•2 (Glucose reacts with acetic anhydride to give two isomeric penta-acetates which do not react with hydroxyl amine to form oxime indicating absence of aldehydic group

C=O + NH2-OH C=N-OH ????

Hydroxyl amine oxime

IR spectra

Warfarin

C=OAbsorption band

Chemical Reactions Related to Color Tests of Carbohydrates•1 (Molisch’s test:

– Any carbohydrate + Alcoholic -naphthol then add conc. H2SO4 on the wall of the test tube Violet ring between the two layers.

•2 (Effect of conc. acids: Treatment with conc. mineral acid (HCl or H2SO4) leads to

dehydration of sugars and formation of the corresponding furfural.

O CHOHOH2C

Pentoses

Hexoses

Furfural(volatile)

5-Hydroxymethyl furfural

(less volatile)

Dehydration

•Reaction of furfural with amines resulted in Schiff’s bases with different colors used as color tests.

•3 (Furfural test (Differentiate between Pentoses and Hexoses):

–Pentose + conc. acid and heat, expose the vapours to Aniline acetate paper Red colour

–Hexoses give negative result.

4 (Resorcinol test (for keto-hexoses):Sugar solution + few crystals of Resorcinol + Equal volume of conc. HCl and warm on water bath Rose Red Colour.

55 ) )Ozazone TestOzazone Test::

•Sugar (H2O)+ phenyl hydrazine HCl+ NaAc, heat (50 min), cool examine ozazone crystals under the microscope. The ozazone are yellow, crystalline with sharp m.p. Glucose, mannose fructose will give the same crystals (reaction involves C-1 and C-2) due to destruction of asymmetric center at C-2 .

CHOH3 PhNH-NH2

CH=N-NH-Ph

Ozazone crystals

+ Ph-NH2 + NH3

)characteristic(

phenyl hydrazine HCl

6 (Effect of Alkalis•Strong alkalis: Polymerization

• Weak alkalis: Isomerization e.g.

OHCH2OH

D-Glucose D-Fructose

D- Mannose

intermediate

7 (Oxidation:

•a) Mild Oxidation:•These are oxidizing agents like Bromine water (or I2) that convert the CHO group

to COOH to produce “onic acids.”•Colour tests based on this reaction:

–Fehling’s reduction test:Sugar solutions + Fehling’s A (CuSO4) + Fehling’s B (NaOH and Na,K tartarate,

Rochell salt), heat on water bath Red Precipitate

RCHO + Cu++ RCOOH + Cu2O (ppt cuprous oxide)

D-Glucose

Gluconic acid

I2 or Fehling's

–Barfoed’s test:

Sugar solution + Barfoed’s reagent (Cu Acetate/Acetic acid),

heat for 3 minutes on boiling water bath Red ppt with monosaccharides only.

* Acidic medium decreases the oxidation power of Cu++.

b) Strong Oxidation:

•These are oxidizing agents like HNO3 that convert the CHO and CH2OH group to COOH to produce

“aric acids.”

D-Glucose

Saccharic acid

•Glalactaric acid (Mucic acid) test:–Oxidation of galactose resulted in the formation of Galactaric acid. It is a

meso compound insoluble in water and have zero optical rotation.

D-Galactose

Galactaric acid

Plane ofsymmetry

Meso comp. (no optical rotation)

c) Enzymatic oxidation:

•Takes place in plants and resulted in the oxidation of the primary alcohol group only producing “uronic acids.”

D-Glucose

Glucuronic acid

8 (Reduction

•This resulted in the reduction of the CHO to CH2OH producing “Sugar Alcohols”. Sodium borohydride or H2/Pt are examples of reducing agents.

D-Glucose

Sorbitol

PentosesExamples:

-D-Ribose: found in all plant and animal cells as the carbohydrate part of nucleic acids e.g. ribonucleic acid (RNA).

-D-Xylose (or wood sugar): prepared from corncobs, bran, straw (or any woody material) by boiling with acids, fermenting out any glucose present with yeast, and crystallizing the D-xylose from the evaporated solution .

-L-Arabinose (or pectin sugar): found in gums, pectic substances, accompanying hemicelluloses and forms the sugar part of several glycosides.

L-Arabinose D-Ribose D-Xylose

Hexoses1 (-D-Glucose

)dextrose, grape sugar, blood sugar or common sugar(

•Occurrence: Widely distributed in nature. Present in Grape and blood .

•Preparation: •D-Glucose is commercially prepared from starch by:

•Autoclaving (at 150 0C) an aqueous starch suspension (15-20%) with dilute acid (0.03 N hydrochloric acid) for 30 minutes (complete hydrolysis).

D-Glucose

OCH2OH

D-Glucopyranose

Uses: -As source of energy (nutrient) either by mouth or IV injection. -IV solutions to restore blood volume. -Shocks following insulin administration. -As osmotic diuretic. -Sweetening agent for Pharmaceutical preparations, ice-cream and candy.

•Liquid glucose:–Preparation:

• It is prepared by partial acid hydrolysis of starch using dilute hydrochloric acid and heating for 20 minutes at about 30 pounds pressure.

–Composition:•It consists of a mixture of glucose, dextrin, maltose and

water .–Uses:

• Used as sweetening agent, as substitute for sucrose and as an excipient in massing pills.

2 -Fructose

•Preparation: •a) Acid hydrolysis of Inulin.

•b) Hydrolysis of Sucrose.

SucroseAcid or Enzyme

Fructose + Glucose

Ca(OH)2

Ca fructosateppt

Ca glucosateSolution

solution

Hydrolysis

•Test for ketoses:•Fructose + HCl + resorcinol, heat red color

•Fructose + CaCl2 ppt

•Uses:•- Infant food-.

•- Diabetic food ???? (low glycemic factor). • - Diet control

D-(-)-Fructose

CH2OHHO

-D-(-)-Fructofuranose

“furanose structure”

Deoxy-sugars

Rhamnose

Digitoxose

Cymarose

They are of little occurrence, common in cardiac glycosides

6-deoxy sugar 2,6-deseoxy sugar 2,6-deseoxy sugar

cardiac glycosides

Keller Kelliani TestKeller Kelliani Test::• 2-Deoxy sugars gives positive results whether in the free

state or in glycosidic combinations:

•Dissolve sample in glacial acetic acid containing FeCl3, add H2SO4 containing FeCl3 on the wall of test tube. An intense green color develops at the interface between the two layers, then spreads into the acetic acid layer (upper layer).

Digitoxose

Cymarose

Some MonosaccharideMonosaccharide derivatives in Pharmacy

•1 (Gluconic acid and its salts:–Preparation:

•Gluconic acid is prepared from glucose by mild oxidation using either dilute HNO3 or Br2/Na2CO3 or Electrically or by

fermentation using Acetobacter aceti.

–Uses:

•Ca gluconate is used (by i.v. or orally) for treatment calcium deficiency.

•Ferrous gluconate, (orally or by i.v.) is used in iron deficiency.

•These salts are characterized by being more easily absorbed than other Ca or Fe salts.

• 2 )Glucuronic Acid: Naturally present in Gums and Mucilage's. It can be prepared by Enzymatic oxidation of glucose.Uses:Treatment of certain arthritic condition as it is a component of cartilages, joint capsules and fluids, nerve sheath and tendons.

3)Aurothioglucose:•Also known as gold thioglucose, water soluble

Treatment of rheumatic arthritis by IM injection.•Not uniformly effective.

OCH2OH

Aurothioglucose

•Auranofin:It is the alkyl Phosphine Gold complex with Acetylated thioglucose.Treatment of rheumatic arthritis orally.

OCH2OR

Auranofin

R= COCH3

P(C2H5)3

•4 (Sorbitol and Mannitol:•sugar alcohols

–Preparation:•Sorbitol is prepared by reduction of glucose and mannitol

by reduction of mannose.

–Uses:•Sorbitol is used as sweetening agent in dietetic food (not

absorbed), chewing gum&tooth pastes. Test of kidney function (iv), not metabolized .

•Mannitol is used as an osmotic diuretic, laxative, and in tests of kidney function (not metabolized if i.v.),

vasodilator (mannitol hexanitrate) ,

5 (Glucosamine

Source: strong acid hydrolysis of chitin (shells of crustaceae)

Uses : regeneration of cartilage (as sulphate salt) in joint injuries and arthritis

OCH2OH

6 (Ascorbic acid•Preparation:

•-extraction from citrus fruits• -synthesis from glucose

•Uses:•-Cure its deficiency (scurvy), cold, capillary fragility

•-Antioxidant in some pharmaceutical preparations

Vitamin C

Dr. Ashraf Taha Khalil. Carbohydrates Definition Organic compounds composed of C, H and O with H and...

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