25-1 Carbohydrates Chapter 25. 25-2 Carbohydrates Carbohydrate: Carbohydrate: A polyhydroxyaldehyde, a polyhydroxyketone, or a compound that gives

25-25-11

CarbohydratesCarbohydrates

Chapter 25Chapter 25

25-25-22

CarbohydratesCarbohydrates

Carbohydrate:Carbohydrate: A polyhydroxyaldehyde, a polyhydroxyketone, or a compound that gives either of these compounds after hydrolysis.

Monosaccharide:Monosaccharide: A carbohydrate that cannot be hydrolyzed to a simpler carbohydrate.• They have the general formula CCnnHH2n2nOOnn, where nn varies

from 3 to 8.• AldoseAldose:: a monosaccharide containing an aldehyde

group.• KetoseKetose:: a monosaccharide containing a ketone group.

25-25-33

Importance of Carbohydrates to us….Importance of Carbohydrates to us….

CO2+ H2O

photosynthesis

chlorophylllight

glucose

polymerizecellulosegiving structure to plants

polymerize

starch, plant seeds

eaten by animals

glucose glycogen (liver)CO2+H2O+energy

clothing fiberwood

25-25-44

MonosaccharidesMonosaccharides

Monosaccharides are classified by their number of carbon atoms:

Hexose

HeptoseOctose

TrioseTetrose

Pentose

FormulaNameC3H6O3C4H8O4

C5H10O5C6H12O6

C7H14O7C8H16O8

25-25-55

MonosaccharidesMonosaccharides

There are only two trioses:

These compounds are referred to simply as trioses, tetroses, and so forth tellling the number of carbon atoms present.

Dihydroxyacetone (a ketotriose)

Glyceraldehyde (an aldotriose)

CHO

CHOH

CH2OH

CH2OH

C=O

CH2OH

Chiral CenterR and S stereoisomers

25-25-66

Review Fischer ProjectionsReview Fischer Projections

Fischer projection:Fischer projection: A two dimensional representation for showing the configuration of carbohydrates.• Horizontal lines represent bonds projecting forward. • Vertical lines represent bonds projecting to the rear.• The more highly oxidized carbon is shown at the top.

C

CHO

CH2OH

OHH

CHO

CH2OH

OHH

(R)-Glyceraldehyde(three-dimensional

representation)

convert to aFischer projection

.

(R)-Glyceraldehyde(Fischer projection)

25-25-77

D,L MonosaccharidesD,L Monosaccharides

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

CHO

H OH

CH2OH

CHO

CH2OH

HHO

D D

L-Glyceraldehyde(S)-Glyceraldehyde

D-Glyceraldehyde(R)-Glyceraldehyde

[]25 = +13.5 []25 = -13.5

25-25-88


According to the conventions proposed by Fischer:• D-monosaccharide:D-monosaccharide: A monosaccharide that has the

same configuration at its penultimate (next to bottom) carbon as D-glyceraldehyde; that is, its -OH is on the right when written as a Fischer projection.

• L-monosaccharide:L-monosaccharide: A monosaccharide that has the same configuration at its penultimate carbon as L-glyceraldehyde; that is, its -OH is on the left when written as a Fischer projection.

25-25-99

D-aldotetroses and the two most abundant D-aldopentoses in the biological world:


D-Erythrose D-Threose D-Ribose 2-Deoxy-D-ribose

CH2OH

CHO

OH

OHH

H

CH2OH

CHO

OH

HHO

H

CH2OH

CHO

OH

OHH

H

CH2OH

CHO

OH

HH

H

OHH OHH

D-aldotetroses D-aldopentosesExpect four stereoisomer 22 for aldotetroses. Two D and two L.

Expect total of 8 (=23) steroisomers. Four D, four L.

25-25-1010


The most abundant hexoses:CHO

HOHH

HOOHH

CH2OHOHH

HHO

CH2OHOHH

CHO

HOHH

HO

CH2OH

HHOC

OHH

CH2OHOHH

O

D-FructoseD-Glucose D-Galactose

aldohexoses ketohexose

Expect 16 stereoisomers 24 for aldohexoses. Eight D and eight L.

Expect 8 stereoisomers 24 for ketohexoses. Four D and four L.

25-25-1111

D Aldohexoses binary displayD Aldohexoses binary display

CHO

OHH

OHH

OHH

OHH

CH2OH

D-Allose

CHO

HHO

OHH

OHH

OHH

CH2OH

D-Altrose

CHO

OHH

HHO

OHH

OHH

CH2OH

D-Glucose

D-Mannose

CHO

HHO

HHO

OHH

OHH

CH2OH

D-Gulose

CHO

OHH

OHH

HHO

OHH

CH2OH

D-Idose

CHO

HHO

OHH

HHO

OHH

CH2OH

D-Galactose

CHO

OHH

HHO

HHO

OHH

CH2OH

D-Talose

CHO

HHO

HHO

HHO

OHH

CH2OH

There is also the L series, the mirror image structures

All altruists gladly make gum in gallon tanks.

L.Fieser

0= 000 1=001 2=010 3=011

4=100 5=101 6=110 7=111

25-25-1212

Amino SugarsAmino Sugars

Amino sugar:Amino sugar: A sugar that contains an -NH2 group in place of an -OH group.• Only three amino sugars are common in nature• N-Acetyl-D-glucosamine is a derivative of D-

glucosamine.CHO

OHOHHNH2

HH

HOH

CH2OH

CHO

OHOHHH

HH

HOH2N

CH2OH

CHO

OHOHHNHCCH3

HH

HOH

CH2OH

OCHO

OHHHNH2

HHOHO

H

CH2OH

D-Glucosamine D-Galactosamine N-Acetyl-D-glucosamine

4

2

D-Mannosamine

25-25-1313

Physical PropertiesPhysical Properties

Monosaccharides are colorless crystalline solids, very soluble in water, but only slightly soluble in ethanol.• sweetness relative to sucrose:

Carbohydrate

Fructose

Glucose

Galactose

Sucrose (table sugar)

Lactose (milk sugar)

Honey

SweetnessRelative to Sucrose

1.74

1.000.970.74

0.320.16

Invert sugar 1.25

Artificial Sweetener

SweetnessRelative to Sucrose

Maltose 0.33

Saccharin 450Acesulfame-K 200Aspartame 160

25-25-1414

Cyclic StructureCyclic Structure

Monosaccharides have hydroxyl and carbonyl groups in the same molecule and those with five or more carbons exist almost entirely as five- and six-membered cyclic hemiacetals.• Anomeric carbon:Anomeric carbon: The new stereocenter created as a

result of cyclic hemiacetal formation.• Anomers:Anomers: Carbohydrates that differ in configuration at

their anomeric carbons named and .

25-25-1515

Haworth ProjectionsHaworth Projections

Haworth projections• Five- and six-membered hemiacetals are represented

as planar pentagons or hexagons viewed through the edge.

• They are commonly written with the anomeric carbon on the right and the hemiacetal oxygen to the back right.

• The designation - means that the -OH on the anomeric carbon is cis to the terminal -CH2OH; - means that it is trans to the terminal -CH2OH.

25-25-1616


CHO

OH

H

OH

H

HO

H

H OH

CH2OH

HH OH

HHO

HOH()

OH

H

CH2OHO

C

H OH

HHO

HOH

H

CH2OHOH

O

H

OH()H OH

HHO

HH

OH

H

CH2OHO

D-Glucose

-D-Glucopyranose (-D-Glucose)

-D-Glucopyranose (-D-Glucose)

anomeric carbon

+

anomericcarbon

5

5

1

1

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

cis, trans,

Lay molecule on side.to

p

25-25-1717


• Six-membered hemiacetal rings are shown by the infix -pyranpyran-.

• Five-membered hemiacetal rings are shown by the infix -furanfuran-.

OO

PyranFuran

25-25-1818

Conformational FormulasConformational Formulas

• Five-membered rings are so close to being planar that Haworth projections are adequate to represent furanoses.

OH ()

H

OH

HOHOCH2

HOH

H

HOCH2

H

OH ()

HOH H

H HO

-D-Ribofuranose(-D-Ribose)

-2-Deoxy-D-ribofuranose(-2-Deoxy-D-ribose)

25-25-1919


• Other monosaccharides also form five-membered cyclic hemiacetals.

• Here are the five-membered cyclic hemiacetals of D-fructose, a ketohexose.

HO

HOCH2 OH

HHO

CH2OH

OHH H

C=O

CH2OH

HOH

CH2OH

OHH

HO HOH

HOHOCH2

HO HCH2OH

OH

D-Fructose

1

2

3

4

5

6

55

1

22

()

-D-Fructofuranose(-D-Fructose)

-D-Fructofuranose(-D-Fructose)

()

1

25-25-2222

Conformational Formulas; Conformational Formulas; to to conversion conversion

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

OH

HO

H

HO

H

HOHH

OH

OH

OHH

HO

H

HO

H

HOHH

O

OH

OH

HO

H

HO

H

OHOHH

H

OH

OH

H

HO

H

HO

H

OOHH

H

OH

-D-Glucopyranose(-D-Glucose)

-D-Glucopyranose(-D-Glucose)

rotate aboutC-1 to C-2 bond

Open chain form

25-25-2323


• The orientations of groups on carbons 1-5 in the Haworth and chair projections of -D-glucopyranose are up-down-up-down-up.

OCH2OH

HOHO

OHOH()H

H OH

HHO

HOH()

OH

H

CH2OH

O

-D-Glucopyranose(chair conformation)

-D-Glucopyranose(Haworth projection)

123

4

5

6

1

23

4

5

6

25-25-2424

MutarotationMutarotation

MutarotationMutarotation:: The change in specific rotation that occurs when an or form of a carbohydrate is converted to an equilibrium mixture of the two.

+80.2

+80.2+52.8

+150.7-D-galactose-D-galactose

[] afterMutarotation[]Monosaccharide

% Present atEquilibrium

2872

64

36-D-glucose-D-glucose

+112.0+18.7

+52.7+52.7

OHOH

HOHO

CH2OHO O

CH2OH

HO

HOOH

HO

[]D25 +18.7

-D-Glucopyranose-D-Glucopyranose

()

()

[]D25 +112

25-25-2525

Hemiacetals and Acetals, carbonyls and alcoholsHemiacetals and Acetals, carbonyls and alcohols

(Unstable in Acid; Stable in base)

(Unstable in Acid; Unstable in base)

Addition reaction.

Substitution reaction

25-25-2626

GlycoGlycosidessides, anomeric OH becomes OR, acetal formation., anomeric OH becomes OR, acetal formation.

Glycoside:Glycoside: A carbohydrate in which the -OH of the anomeric carbon is replaced by -OR.• methyl -D-glucopyranoside (methyl -D-glucoside)

HH OH

HHO

HOH

OH

H

CH2OHO

CH3OH H+

-H2O

OCH2OH

H

OH

OCH3H

HOH

OHH

H

OCH2OH

H

OH

HH

HOH

OHHOCH3

(-D-Glucose)-D-Glucopyranose Methyl -D-gluco-

pyranoside(Methyl -D-glucoside)

++

Methyl -D-gluco-pyranoside

(Methyl -D-glucoside)

glycosidicbond

25-25-2727

Glycosides, acetalsGlycosides, acetals

Glycosidic bond:Glycosidic bond: The bond from the anomeric carbon of the glycoside to an -OR group.

Glycosides are named by listing the name of the alkyl or aryl group bonded to oxygen followed by the name of the carbohydrate with the ending -e-e replaced by -ide-ide.• methyl -D-glucopyranoside• methyl -D-ribofuranoside

25-25-2828

NN-Glycosides-Glycosides

The anomeric carbon of a cyclic hemiacetal also undergoes reaction with the N-H group of an amine to form an N-glycoside.• N-glycosides of the following purine and pyrimidine

bases are structural units of nucleic acids.

HN

NH

O

O

Uracil

N

NH

O

NH2

Cytosine

HN

NH

O

O

Thymine

CH3N

N N

N

H

NH2

HN

N N

N

H

O

H2N

Adenine Guanine

25-25-2929

NN-Glycosides-Glycosides

• The -N-glycoside formed between D-ribofuranose and cytosine.

H

H

H

H

OHOCH2

HO OH

NH2

O

N

N

anomericcarbon

a -N-glycosidicbond

25-25-3030

ReactionsReactions

25-25-3131

Reduction to Alditols, aldehyde Reduction to Alditols, aldehyde alcohol alcohol

The carbonyl group of a monosaccharide can be reduced to an hydroxyl group by a variety of reducing agents, including NaBH4 and H2/M.

OHOH

HOHO

CH2OHO

CHOOHHHHOOHH

CH2OHOHH

NaBH4

CH2OHOHHHHOOHH

CH2OHOHH

D-Glucitol(D-Sorbitol)

D-Glucose-D-Glucopyranose

An alditol

25-25-3232

Other alditolsOther alditols

• Other alditols common in the biological world are:

CH2OH

CH2OH

OHHOHH

CH2OH

CH2OH

OHHHHOOHH

CH2OHHHOHHOOHH

CH2OHOHH

D-Mannitol XylitolErythritol

25-25-3333

OxidationsOxidations

Oxidation can be done in several ways.

Tollens reagent (Ag+(NH3)2 or Benedict’s solution (Cu2+ tartrate complex). Not synthetically useful due to side reactions.

Bromine water oxidizes aldoses (not ketoses) to monocarboxylic acids (Aldonic Acids).

Nitric Acid oxidizes aldoses to dicarboxylic acids (Aldaric acids).

Enzyme catalyzed oxidation of terminal OH to carboxylic acid (Uronic Acid)

Periodic Acid oxidizes and breaks C C bonds. Later for that.

25-25-3434

Reducing SugarsReducing Sugars

Sugars with aldehyde (or ketone group) in solution. The group can be oxidized and is detected with Tollens or Benedicts solution. Ketone groups converted to aldehyde via tautomeric shifts (later).

25-25-3535

Problem with TollensProblem with Tollens

2-Ketoses are also oxidized to aldonic acids in basic solution (Tollens).

An aldoseAn enediolA 2-ketose

CH2OHC=O

CH2OH

C-OH

CH2OH

CHOH

CHOH

CH2OH

CHO

(CHOH)n (CHOH)n (CHOH)n

An aldonic acid

CHOH

CH2OH

COOH

(CHOH)n

(1) (2) (3)

Ketose to aldose conversion via keto enol tautomerism

Oxidation

Reducing sugar

25-25-3737

Oxidation to carboxylic acidsOxidation to carboxylic acids

CHO

OHH

HHO

OHH

OHH

CH2OH

Br2 water

HNO3

CO2H

OHH

HHO

OHH

OHH

CH2OH

CO2H

OHH

HHO

OHH

OHH

CO2H

Aldonic Acid

Aldaric Acid

25-25-3838

Oxidation to Uronic AcidsOxidation to Uronic Acids

Enzyme-catalyzed oxidation of the terminal -OH group gives a -COOH group.

CHO

CH2OH

OHHHHOOHHOHH

CHO

COOH

OHHHHOOHHOHH

HOHO

OHOH

COOHO

D-Glucose

enzyme-catalyzedoxidation

D-Glucuronic acid(a uronic acid)

25-25-4040

Oxidation by periodic acid, HIOOxidation by periodic acid, HIO4 4 or H or H55IOIO66

Periodic acid cleaves the C-C bond of a glycol.

+

Periodic acid

A cyclic periodic ester

+

A 1,2-diol

Iodic acid

C

C OH

OHI

OHHO

HO

O

C O

C O C

C

OHOH

IOH

OH

OOH

-2H2O

H3IO4

O

O

25-25-4141

Oxidation by HIOOxidation by HIO44

• It also cleaves -hydroxyketones

• and -hydroxyaldehydes.

C OH

C

R

H

H

OH2O

OHC

C

H

H

HO

R

OH H5IO6

C O

R

HO

C OH

H

Hydratedintermediate

-Hydroxyketone

+

C

C

O

H

H

R

OHH2O

C OH

C

R

H

H

OH

OHH5IO6

C

OH

H O

CH

R

O

-Hydroxyaldehyde

+

Hydratedintermediate

25-25-4242

Examples. Identify each of the glucose derivativesExamples. Identify each of the glucose derivatives..

A + 4 HIO4 yielded 3 HCO2H + HCHO + OHC-CO2H

B + 5 HIO4 yielded 4 HCO2H + 2 HCHO

C + 3 HIO4 yielded 2 HCO2H + 2 OHC-CO2H

Analysis of A:4 moles of periodic acid used. 4 bonds broken.Products:Formic acid from –CHOH- or CHO-.Formaldehyde from CH2OH-OHC-CO2H from –CHOH-CO2H

CO2H

OHH

HHO

OHH

OHH

CH2OH

25-25-4343

Another exampleAnother example

Oxidation of methyl -D-glucoside consumes two moles of HIO4 and produces one mole of formic acid, which indicates three adjacent C-OH groups.

OCH3OH

HOHO

CH2OHO 2 HIO5

C

H

OHO OCH3

H

O

H

CH2OHC

OC

O

Methyl -D-glucopyranoside

periodic acid cleavageat these two bonds

2 HIO4

25-25-4444

Osazones, EpimersOsazones, Epimers

CHO

CHOH

3 PhNHNH2CH=NNHPh

C=NNHPh

osazone

PhCHO

O

O

osonealdose

25-25-4545

Use of osazone in structure determinationUse of osazone in structure determination

Fischer found that (+) glucose and (+) mannose yielded the same osazone indicating that they differed only at the C2 configuration. Hence, if we know the configuration of (+) glucose we immediately have that of (+) mannose. Stereoisomers that differ in configuration at only one stereogenic center are called epimers. D-glucose and D-mannose are epimers.

CHO

OHH

HHO

OHH

OHH

CH2OH

CHO

HHO

HHO

OHH

OHH

CH2OH

HC

PhHNN

HHO

OHH

OHH

CH2OH

NNHPH

D glucose D mannose

25-25-4646

Glucose Assay: diabetes (background)Glucose Assay: diabetes (background)

The analytical procedure most often performed in the clinical chemistry laboratory is the determination of glucose in blood, urine, or other biological fluid.

25-25-4747

Glucose AssayGlucose Assay

The glucose oxidase method is completely specific for D-glucose.

25-25-4848

Glucose AssayGlucose Assay

• The enzyme glucose oxidase is specific for -D-glucose.

• Molecular oxygen, O2, used in this reaction is reduced to hydrogen peroxide H2O2.

• The concentration of H2O2 is determined experimentally, and is proportional to the concentration of glucose in the sample.

• In one procedure, the hydrogen peroxide oxidizes o-toluidine to a colored product, whose concentration is determined spectrophotometrically.

25-25-4949

Killani-Fischer lengthening of chainKillani-Fischer lengthening of chain

CHO

HHO

OHH

OHH

CH2OH

D Arabinose

HCN

CN

OHH

HHO

OHH

OHH

CH2OH

CN

HHO

HHO

OHH

OHH

CH2OH

+

epimers

aq acid

CO2H

OHH

HHO

OHH

OHH

CH2OH

CO2H

HHO

HHO

OHH

OHH

CH2OH

+

CHO

OHH

HHO

OHH

OHH

CH2OH

CHO

HHO

HHO

OHH

OHH

CH2OH

+Na

Get both epimers.

As lactones

25-25-5050

Ruff Degradation shortening of chainRuff Degradation shortening of chain

CHO

OHH

HHO

OHH

OHH

CH2OH

Br2

CO2H

OHH

HHO

OHH

OHH

CH2OH

CaCO3

CO2- )2 Ca+2

OHH

HHO

OHH

OHH

CH2OH

H2O2

CHO

HHO

OHH

OHH

CH2OH

Fe+3

25-25-5151

Fischer proof of structure of glucoseFischer proof of structure of glucose

Emil Fischer received the 1902 Nobel prize for determining the structure of glucose.

What was available to him in 1888?

•Theory of stereoisomerism•Ruff degradation •Oxidation to aldonic and aldaric acids•Killani-Fischer synthesis•Various aldohexoses and aldopentoses

25-25-5252

Fischer proof of structure of glucoseFischer proof of structure of glucose

CHO

CH2OH

glucose known to be an aldohexose but of unknown structure

four chiral centers.16 stereoisomers, 8 pairs of enantionmers, 8 D and 8 L

Fischer could not work with absolute configurations. He assumed that naturally occuring glucose was D.He had to work out the relationship of the other three OH.

OH

25-25-5353

Fischer started with the aldopentosesFischer started with the aldopentoses

CHO

CH2OH

three chiral centers

8 stereoisomers = 4 pairs of enantiomers = 4 L + 4 D

One monosaccharide that was available was (-) arabinose, an aldopentose.

Again, Fischer could not work with absolute configurations. He assumed that naturally occuring (-) arabinose was D.He had to work out the relationship of the other two OH.

OH

25-25-5454

Experiments on (-) arabinoseExperiments on (-) arabinose

CHO

OH

CH2OH

assumed partialstructure of (-) arabinose

Fact: Nitric acid oxidation of (-) arabinose yielded an optically active aldaric acid

CO2H

HO

OH

CO2H

optically active

HNO3

Conclusion: (-) arabinose is either

CHO

HO

OH

OH

CH2OH

CHO

HO

HO

OH

CH2OH

or

Must be an OH here

25-25-5555

Use KF to get aldohexosesUse KF to get aldohexoses

CHO

HO

OH

CH2OH

partialstructure of arabinose

Fact: Killani Fischer synthesis on (-) arabinose yielded (+) glucose and (+) mannose

K. F.

CHO

OH

HO

OH

CH2OH

CHO

HO

HO

OH

CH2OH

+

mixture of + glucose and + mannose,both of unknown structure. Which is glucose is unknown.

25-25-5656

Aldaric acids from glucose and mannoseAldaric acids from glucose and mannose

Fact: nitric acid oxidation of either glucose or mannose yields optically active aldaric acids. This locates the OH on C4 since both aldaric acids have to be active.

CHO

OH

HO

OH

OH

CH2OH

CHO

HO

HO

OH

OH

CH2OH

+

Each yields optically active aldaric acid.

CHO

OH

HO

HO

OH

CH2OH

CHO

HO

HO

HO

OH

CH2OH

+

yields opticallyinactive aldaric

yields opticallyactive aldric

C4 OH on right C4 OH on left

25-25-5757

Which is glucose??Which is glucose??

CHO

OH

HO

OH

OH

CH2OH

CHO

HO

HO

OH

OH

CH2OH

+

A B

Which one, A or B, is glucose is determined by preparing the aldaric acids (dicarboxylic acids).

25-25-5858

Final piece of data…Final piece of data…

Fact: the aldaric acid from (+)glucose is also produced by nitric acid oxidation of a different aldohexose, (+)gulose.

CHO

HO

HO

OH

OH

CH2OH

CHO

OHH

HHO

OHH

OHH

CH2OH

HNO3

CO2H

OH

HO

OH

OH

CO2H

CH2OH

OH

HO

OH

OH

CHO

HNO3

A (+) gulose which turns outto be an L aldohexosestructure of glucose

aldaric acid fromA.

Aldaric acid from Bcomes only from B, (+) mannose

25-25-5959

Where are we?Where are we?

We have determined the straight chain structure of (+) glucose. But certain data indicates the problem is not yet solved.

Glucose does not give some reactions characteristic of aldehydes• A qualitative test, Schiff test, for aldehydes is negative.• Bisulfite addition products cannot be made

Mutarotation changes specific rotation. Glucose is converted into two acetals (the methyl

D-glucosides), not hemiacetals, by reaction with one mole of methanol (acid).

Conclude: glucose is a cyclic hemiacetal.

25-25-6060

Now to determine ring size.Now to determine ring size.

We can methylate the various OH groups, converting them into OMe. Two kinds of OH•OH at anomeric carbon•OH on backbone

One of the backbone OH groups may be bonded to the anomeric carbon to form a ring. We seek to detect which one.

First review characteristics of hemiacetals and acetals.

25-25-6161

Hemiacetals and Acetals, carbonyls and alcoholsHemiacetals and Acetals, carbonyls and alcohols

(Unstable in Acid; Stable in base)

(Unstable in Acid; Unstable in base)

Addition reaction.

Substitution reaction

25-25-6262

Methylation to find ring size.Methylation to find ring size.

O

H

HO

H

HO

H

H

OHH

OH

HO

CH3OH

dry HCl

O

H

HO

H

HO

H

H

OHH

OCH3

HO

Methyl D glucoside

(CH3O)2SO2,NaOH

O

H

H3CO

H

H3CO

H

H

OCH3H

OCH3

H3CO

dil HCl O

H

H3CO

H

H3CO

H

H

OCH3H

OH

H3CO

CHO

OCH3H

HH3CO

OCH3H

OHH

OCH3

C4 - C5 cleavage

C5 - C6 cleavage

oxidation

HNO3

CO2H

OCH3H

HH3CO

CO2H

C4 - C5 cleavage

+

CO2H

OCH3H

HH3CO

OCH3H

CO2H

C5 - C6 cleavage

The observed 4 carbon and 5 carbon dicarboxylic acids indicate free OH was on C5.

25-25-6363

Conformation of the pyranose ring.Conformation of the pyranose ring.

Ring flips can occur. Generally the conformation with large groups equatorial dominate.

Generally the CH2OH should be made equatorial

OO

HOH2CCH2OH

OH

HO

HOHO

OH

OH

OH

OH

more stableless stable

-D glucopyranose

25-25-6464

Extreme case: a-D-IdopyranoseExtreme case: a-D-Idopyranose

O

OH

H

HO

H

OH

HO

HH

HOH2C

HO

CH2OH

OHOH

HO

HO

-D-Idopyranose

axial

more stable

25-25-6565

disaccharidesdisaccharides

Sucrose, table sugar Maltose, from barley Lactose, milk sugar

25-25-6666

Sucrose, table sugarSucrose, table sugar

Table sugar, obtained from the juice of sugar cane and sugar beet.

-1, -2 bond

25-25-6767

LactoseLactose

The principle sugar present in milk, 5 – 10%.

25-25-6868

MaltoseMaltose

From malt, the juice of sprouted barley and other cereal grains.

25-25-6969

Structure Determinatin of (+) MaltoseStructure Determinatin of (+) Maltose

Experimental Facts C12H22O11

Positive for Tollens and Fehlings solution, reducing sugar

Reacts with phenylhydrazine to yield osazone, C12H20O9(NNHC6H5)2

Oxidizes by bromine water to monocaboxylic acid.

Exists in two forms which undergo mutarotation.

Consistent with two aldoses linked together with one hemiacetal group.

25-25-7070

More data…..More data…..

Maltose undergoes hydrolysis with aq. acid or maltase to yield two D (+) glucose units. Two glucose units joined together: glucose – acetal linkage (glucoside) – glucose – hemiacetal.

Maltase hydrolysis is characteristic of glucosides. Conclude something like

CH2OH

O

CH2OH

OH

25-25-7171

How to proceed…..How to proceed…..

Label the rings and label the free OH groups.CH2OH

O

CH2OH

OH

Br2, H2O

CH2OH

O

CH2OH

OH

CO2H

O O

O

Me2SO4

base

HO

OH

OMe

O

OMe

OMe

CO2HO

MeO

OMe

aq acid

free OHmethylated free OH

methylated

unmethylated

NextSlide

25-25-7272

Hydrolysis productsHydrolysis products

CHO

OMeH

HMeO

OMeH

OHH

CH2OMe

CO2H

OHH

HMeO

OHH

OMeH

CH2OMe

This glucose derivative was the “free” CHO unit, the reducing sugar.

Point of attachment to the other glucose unit.

Not the reducing aldohexose unit (not the carboxylic acid).

Used in hemiacetal link.

Structure on next slide.

25-25-7373

MaltoseMaltose

O

H

HO

H

HO

H

OHHH

OH

O

O

H

H

HO

H

HO

OHHH

OH

25-25-7474

StarchStarch

Starch is used for energy storage in plants• It can be separated into two fractions; amylose and

amylopectin; each on complete hydrolysis gives only D-glucose.

• AmyloseAmylose: A polysaccharide composed of continuous, unbranched chains of up to 4000 D-glucose units joined by -1,4-glycosidic bonds.

• AmylopectinAmylopectin: A highly branched polymer of D-glucose; chains consist of 24-30 units of D-glucose joined by -1,4-glycosidic bonds and branches created by -1,6-glycosidic bonds.

25-25-7575

GlycogenGlycogen

Glycogen is the reserve carbohydrate for animals.• Like amylopectin, glycogen is a nonlinear polymer of

D-glucose units joined by -1,4- and -1,6-glycosidic bonds bonds.

• The total amount of glycogen in the body of a well-nourished adult is about 350 g (about 3/4 of a pound) divided almost equally between liver and muscle.

25-25-7676

CelluloseCellulose

Cellulose: A linear polymer of D-glucose units joined by -1,4-glycosidic bonds.• It has an average molecular weight of 400,000 g/mol,

corresponding to approximately 2800 D-glucose units per molecule.

• Both rayon and acetate rayon are made from chemically modified cellulose.

25-25-7777

Acidic PolysaccharidesAcidic Polysaccharides

Hyaluronic acid:Hyaluronic acid: An acidic polysaccharide present in connective tissue, such as synovial fluid and vitreous humor.

25-25-7878

Acidic PolysaccharidesAcidic Polysaccharides

Heparin• Its best understood function is as an anticoagulant.• Following is a pentasaccharide unit of heparin.

25-25-7979

An example…..An example…..A synthetic polysaccharide is composed of three monosaccharides units in the following order: (D-glucpyranose) – (L-fructofuranose) – (D-altropyranose). The linkages between the units and the structures of the individual D units are given below where the wavy lines are used to avoid specifying configuration.

D-glucopyranose

O

D-fructofuranose

CH2OH

CH2OH

OH

OH

OH

OO

CH2OHCH2OH

D-altropyranose

OH

OH

OHOH

OH

OH

OH

OH

OO O

1,4 linkage linkage anomer

D-Glucose L-Fructose D-Altrose

Add all substituents to the rings and show the linkages between the units. You must show stereochemistry clearly.

25-25-8080

D-glucopyranose

O

D-fructofuranose

CH2OH

CH2OH

OH

OH

OH

OO

CH2OHCH2OH

D-altropyranose

OH

OH

OHOH

OH

OH

OH

OH

OO O

1,4 linkage linkage anomer

D-Glucose L-Fructose D-Altrose

O

SolutionSolution

CH2OH

OH

OH

OH

CH2OH

OH

OH

O

First the D glucose…Now the 1,4 linkNow L fructose

H

Now D-Altrose

CH2OH

OH

OH

OHOH

OHOH

CH2OH

Now the 2,6

CH2

Now the ano mer

OH

CH2OH

Documents

25-1 Carbohydrates Chapter 25. 25-2 Carbohydrates Carbohydrate: Carbohydrate: A polyhydroxyaldehyde, a polyhydroxyketone, or a compound that gives