Carbohydrate

Carbohydrates

Outline

Introduction

Monosaccharides

Disaccharides and Oligosaccharides

Polysaccharides

Acidic polysaccharides

Introduction

NameTriose Tetrose Pentose HexoseHeptose

Formula C3H6O3

C4H8O4 C5H10O5 C6H12O6

C7H14O7

Monosacchrides

Formula CnH2nOn n=3-8

Structure and nomenclature

Aldose - aldehyde/hydroxyl

Ketose – ketone/hydroxyl

D and L Monosaccharides

Fischer Projection Formulas

In 1891, Emil Fischer made the arbitrary assignments of D- and L- to the enantiomers of glyceraldehyde

D-monosaccharide:D-monosaccharide: the -OH on its penultimate (next to last) carbon is on the right

L-monosaccharide:L-monosaccharide: the -OH on its penultimate (next to last) carbon is on the left

Amino sugars

Contain an –NH2 group in place of –OH group

Only three amino sugars

Glucose is produced in plants from CO2 and

H2O via photosynthesis.

Plants convert glucose into other small sugars

and polymers (cellulose, starch).

Dietary carbohydrates provide the major

source of energy required by organisms.

Physical properties

Colorless,crystalline solid

Are very soluble in water

Sightly soluble in ethanol

Insoluble in non-polar solvent diethyl ether,

chloro-form,benzene….

The Cyclic Structure of Monosaccharide

Aldehydes and ketones react with alcohols to form hemiacetalshemiacetals Cyclic hemiacetals form readily when the hydroxyl and

carbonyl groups are part of the same molecule and their interaction can form a five- or six-membered ring

For example:

H4-Hydroxypentanal

A cyclic hemiacetal

redraw to show -OH and -CHO

close to each other

A. Haworth Projections The cyclic structure of monosaccharide is

Haworth projection D-Glucose forms these cyclic hemiacetalsCHO

CH2OHO

CH2OHOH

OHH OH

CH2OHO

D-Glucose

-D-Glucopyranose (-D-Glucose)

anomericcarbon

redraw to show the -OH on carbon-5 close to thealdehyde on carbon-1

A. Haworth Projections

Cyclic hemiacetal is represented as a planar ring, lying roughly perpendicular to the plane of the paper

Groups bonded to the carbons of the ring then lie either above or below the plane of the ring

New carbon stereocenter created in forming the cyclic structure is called an anomeric carbonanomeric carbon

Stereoisomers that differ in configuration only at the anomeric carbon are called anomersanomers

Anomeric carbon of an aldose is carbon 1; that of the most common ketoses is carbon 2.

A. Haworth Projections form: -OH on the anomeric carbon is

on the same side of the ring as the terminal –CH2OH (up)

form: -OH on the anomeric carbon is on the side of the ring opposite from the terminal –CH2OH (down)

Pyranose:Pyranose: 6-member ring sugar containing O

Furanose:Furanose: 5-member ring sugar containing O

PyranFuranOO

A. Haworth ProjectionsD-fructose also forms a five-membered cyclic

hemiacetal

HOCH2 OH

HO HOH

HOHOCH2

HO HCH2OH

D-Fructose

-D-Fructofuranose(-D-Fructose)

B. Conformation Representations

For pyranoses, the six-membered ring is more accurately represented as a chair conformationchair conformation

OCH2OH

OHOH()

CH2OHOHHO

OH()HO

CH2OHO

(-D-Glucose)

-D-Glucopyranose

D-Glucose

anomericcarbon

B. Conformation RepresentationsThe Haworth projection and the chair

conformation, the orientations of groups on carbons 1- 5 of -D-glucopyranose are up, down, up, down, and up

OCH2OH

OHOH()H

CH2OHO

-D-Glucopyranose(chair conformation)

-D-Glucopyranose(Haworth projection)

C. Mutarotation

Mutarotation:Mutarotation: a- and b-anomers can have the ring open and then form the other anomer.A change in specific optical rotation accompanies the equilibration of in aqueous solution Example: when either a-D-glucose or b-D-glucose is dissolved in water, the specific rotation of the solution gradually changes to an equilibrium value of +52.7°, which corresponds to 64% beta and 36% alpha forms

C. Mutarotation

[]D25 = + 18.7°

-D-Glucopyranose-D-Glucopyranose[]D

25 = +112°

CH2OHO HO OH

OCH2OH

Open-chain form

C. Mutarotation

Rings can open to form open chain compound. New ring can be either - or -anomer Equilibrium among - and - forms (and open chain) will be established. Change in specific optical rotation accompanies this equilibration

If either -D-glucose or -D-glucose is dissolved in water, specific rotation changes to an equilibrium value of +52.7° 64% beta and 36% alpha forms at equilibrium Very little will exist in open chain form

C. Mutarotation

Another representation of ring opening and closure

C. Mutarotation

D-Glucose- a cyclic monosaccharideOHOCH2

OHOCH2

OHHOCH2

-D-glucopyranone Open Chain -D-glucopyranone

[] +18.70 +1120

Equilibrium 64% 36%

Mutorotation: Change in specific rotation that accompanies the interconversion of and - anomers in water.

Reaction Of Monosaccharides

A. Fromation of Glycosides (Acetals) The cyclic hemiacetal form of a sugar can react

with an alcohol in the presence of acid to form an acetal

Glycoside: a cyclic acetal derived from a monosaccharideGlycosidic bond: the bond from the anomeric carbon to

the –OR group

Glycosides: are named by the name of the carbonhydrates in which the ending –e is replaceed by –ide.

Example:

acetals of glucose glucosides

acetals of maltose maltosides

ketals of fructonse fructonsides

Just as the anomeric carbon of a cyclic hemiacetal undergoes reaction with the -OH group of an alcohol to form a glycoside, it also undergoes reaction with the N-H group of an amine to form an N-glycoside.

N-Glycosides of these pyrimidine and purine bases are structural units of nucleic acids

Hemi-acetal

N-glycoside

B. Reduction of Monosaccharides

Aldoses( and ketoses) can be reduced with sodium borohydride to compounds called alditols

Sorbitolis used in the manufacture of candies and as a sugar substitute for diabetics. D-Sorbitol is an important food additive, usually added to prevent dehydration of foods and other materials on exposure to air

C. Oxidation to Aldonic Acids

Oxidizing agents such as oxygen (O2), Tollens' reagent (Ag+, NH3), Fehling's reagent (Cu2+, sodium tartrate), Benedict`s reagent (Cu2+ sodium citrate) will oxidize aldehydes to give carboxylic acids

Ketones cannot be oxidized like aldehydesKetoses are reducing sugars if they can isomerize

to aldoses

D. Oxidation to Uronic acid

We learned that primary alcohols can be oxidized to carboxylic acids. Hexoses contain a primary alcohol at C6 which can be oxidized to a carboxylic acid by various enzymes in plants and animals

Enzyme-catalyzedoxidation

E. Oxidation by periodic acid

In this reaction, iodine (VII) of periodic acid is

reduced to iodine (V) of iodic acid.

Disaccharides and Oligosaccharides

Disaccharide: A carbohydrate containing two

monosaccharide units joined by a glycosidic bond.

Oligosaccharide: A carbohydrate containing four to

ten monosaccharide units, each joined to the next by a

glycosidic bond.

Maltose

Lactose is a sugar that is found most notably in milk. Lactose makes up around 2~8% of milk (by weight), although the amount varies among species and individuals. It is extracted from sweet or sour whey. The name comes from lac, the latin word for milk, plus the -ose ending used to name sugars. It has a formula of C12H22O11.

Structure:

When 1 mol of maltose is subjected to acid-catalyzed

hydrolysis, it yield 2 mol of D-(+)-glucose.

Maltose is a reducing sugar.

Maltose exists in two anomeric forms: α-(+)-maltose, and

β-(+)-maltose

Maltose reacts with bromine water to form a

monocarboxylic acid, maltose acid.

Methylation of maltose acid followed by hydrolysis gives

2,3,4,6-tetra-O-methyl-D-glucose and 2,3,5,6-tetra-O-

methyl-D-gluconic acid.

Methylation of maltose itself, followed by hydrolysis,

gives 2,3,4,6-tetra-O-methyl-D-glucose and 2,3,4,6-tri-O-

methyl-D-glucose.

Sucrose

Sucrose: the most widely occurring disaccharide of ordinary table sugar

Structure:

Sucrose has the molecular formula C12H22O11 Acid-catalyzed hydrolysis of 1 mol of sucrose

yields 1 mol of D-glucose and 1 mol of D-fructose. Sucrose is a nonreducing sugar. Neither the

glucose not the fructose portion of sucrose has a hemiacetal or hemiketal group, thus the two hexoses must have a glycoside linkage that involves C-1of glucose and C-2 of fructose.

The hydrolysis of sucrose indicates an α configuration at the glucoside portion and an enzyme known to hydrolyze a β-fructofuranosides.

Methylation of sucrose gives an octamethyl derivative that, on hydrolysis, gives 2,3,4,6-tetra-O-methyl-D-glucose and 1,3,4,6-tetra-O-methyl-D-fructose

Lactose

Lactose is a reducing sugar that hydrolyzes to yield D-glucose and D-galactose; the glycosidic linkage is β.

Structure:

Polysaccharides

Have a general formula of Cx(H2O)y (x:200-2500) or (C6H10O5)n (40n3000).

Are polymeric carbohydrate structure.

Consist of large numbers of monosaccharide units bonded together by glycosidic bonds ( it is formed between the hemiacetal group of a saccharide and the hydroxyl group of some organic compound such as an alcohol).

These structure are often linear, but may contain various degrees of branching.

Are often quite heterogeneous.

Three important polysaccharide are starch, glycogen and cellulose.

Starch

Is a carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds.

Is used for energy storage in plants.

Consists of two types of molecules: the linear and helical amylose and the branched amylopectin.

Contain 20-25% amylose and 75-80% amylopectin.

Pure starch is white, tasteless and odorless powder, insoluble in cold water or alcohol, but soluble in heated water

Amylose

Is composed of unbranched chains of up to 4000 D-glucose units joined by -1,4-glycosidic bonds.

Figure . Amylopectin

Amylopectin

Contains chains up to 10000 D-glucose units joined by -1,4-glycosidic bonds.

At branch points, new chains of 24 to 30 units are started by -1,6-glycosidic bonds.

OHOH2C

-glycosidic bond

-1,4-glycosidic bonds

Applications of starch

Glycogen

Is the energy-reserve carbohydrate for animals.

Is a branched polysaccharide of approximately

106 glucose units joined by -1,4- and -1,6-

glycosidic bonds.

Divided almost equally between liver and

muscle.

Cellulose

Figure . Cellulose.

-1,4-glycosidic bonds

Has the formula (C6H10O5)n.

Is a linear polysaccharide of D-glucose units joined by -1,4-glycosidic bonds.

Has an average molecular weight of 400000g/mol.

Is the structural component of the primary cell wall of green plants, many forms of algae,...

Has no taste, is odourless, is hydrophilic, is insoluble in water and most organic solvents.

Humans and other animals have only -glucosidases in digestion system no use cellulose as food

Textile fibers from cellulose

Cotton is almost pure cellulose.

Both rayon and acetate rayon are made from chemically modified cellulose and were the first commercially important synthetic textile fibers.

In the production of rayon:

Cellulose-OHNaOH

Cellulose- O NaS=C=S

Cellulose-O-S-S Na

San -OH group in a cellulose fiber

Sodium salt of a xanthate ester (a viscous colloidal suspension)

Cellulose (insoluble in water)

In the industrial synthesis of acetate rayon, cellulose is treated with acetic anhydride.

+3CH3COCCH3

+ CH3COOH

A glucose unit in a cellulose fiber

Acetic anhydride

A fully acetylated glucose unit

Acidic Polysaccharide

A group of polysaccharides contain carboxyl

groups and/or sulfuric ester groups.

Play important roles in the structure and

function of connective tissue.

There is no single general type of connective

tissue.

Hyaluronic Acid

Is the simplest acidic polysaccharide present in connective tissue.

Has a molecular weight of between 105 and 107g/mol.

Contains from 3000-100000 repeating units.

Is most abundant in embryonic tissues and in specialized connective tissue such as the vitreous humor of eye, the lubricant of joints in the body,...

D-glucuronic acid N-acetyl-D-glucosamine

The repeating unit of hyaluronic acid

The repeating disaccharide unit in hyaluronic acid is D-glucuronic acid linked by a -1,3-glucosidic bond to N-acetyl-D-glucosamine.

Heparin

Is a heterogeneous mixture of variably sulfonated polysaccharide chains.

Molecular weight from 6000-30000g/mol.

Is synthesized and stored in mast cell of various tissues: liver, lungs and gut.

Is widely as an injectable anticoagulant.

Binds strongly to antithrombin III.

HO OSO3-

The repeating monosaccharide units of heparin are N-acetyl-D-glucosamine, D-glucuronic acid, D-glucosamine, and L-ioduronic acid bonded by a combination of -1,4- and -1,4-glycosidic bonds.

A pentasaccharide unit of heparin.

http://en.wikipedia.org/wiki/Heparin

http://en.wikipedia.org/wiki/Hyaluronan

http://en.wikipedia.org/wiki/Glycogen

http://vi.wikipedia.org/wiki/Cellulose

http://en.wikipedia.org/wiki/Glycosidic_bond

http://www.daviddarling.info/encyclopedia/P/polysaccharide.html

http://vi.wikipedia.org/wiki/Tinh_b%E1%BB%99t

References

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