Lecture 24- Carbohydrates

General

Organic ChemistryTwo credits

Second Semester 2009

King Saud bin Abdulaziz University for Health Science

Reference Book: Organic Chemistry: A Brief Course, by Robert C. Atkins and Francis A. CareyThird Edition

Instructor: Rabih O. Al-Kaysi, PhD.

Chapter 15Chapter 15

CarbohydratesCarbohydrates

Lecture 24

Classification of CarbohydratesClassification of Carbohydrates

Classification of CarbohydratesClassification of Carbohydrates

monosaccharidemonosaccharide

disaccharidedisaccharide

oligosaccharideoligosaccharide

polysaccharidepolysaccharide

is not cleaved to a simpler carbohydrate on is not cleaved to a simpler carbohydrate on hydrolysishydrolysis

glucose, for example, is a monosaccharideglucose, for example, is a monosaccharide

MonosaccharideMonosaccharide

is cleaved to two monosaccharides on hydrolysis is cleaved to two monosaccharides on hydrolysis

these two monosaccharides may be the these two monosaccharides may be the same or differentsame or different

DisaccharideDisaccharide

CC1212HH2222OO11 11 + H+ H22OO

sucrosesucrose(a disaccharide)(a disaccharide)

is cleaved to two monosaccharides on hydrolysis is cleaved to two monosaccharides on hydrolysis

these two monosaccharides may be the these two monosaccharides may be the same or differentsame or different

DisaccharideDisaccharide

CC1212HH2222OO11 11 + H+ H22OO CC66HH1212OO6 6 + + CC66HH1212OO66

sucrosesucrose(a disaccharide)(a disaccharide)

glucoseglucose(a monosaccharide)(a monosaccharide)

fructosefructose(a monosaccharide)(a monosaccharide)

oligosaccharide:oligosaccharide:

gives three or more monosaccharide units on gives three or more monosaccharide units on hydrolysishydrolysis

polysaccharidepolysaccharide: :

yields more than 10 monosaccharide unitsyields more than 10 monosaccharide units

Higher SaccharidesHigher Saccharides

No. of carbonsNo. of carbons AldoseAldose KetoseKetose

44 AldotetroseAldotetrose KetotetroseKetotetrose

55 AldopentoseAldopentose KetopentoseKetopentose

66 AldohexoseAldohexose KetopentoseKetopentose

77 AldoheptoseAldoheptose KetoheptoseKetoheptose

88 AldooctoseAldooctose KetooctoseKetooctose

Some Classes of CarbohydratesSome Classes of Carbohydrates

Just for general knowledge, will not be tested on

Fischer Projections and Fischer Projections and DD--LL Notation Notation

Fischer ProjectionsFischer Projections

Fischer Projections of EnantiomersFischer Projections of Enantiomers

Enantiomers of GlyceraldehydeEnantiomers of Glyceraldehyde

CHCH OO

CHCH22OHOH

HH OHOHDD

CHCH OO

CHCH22OHOH

HHHOHOLL

(+)-Glyceraldehyde(+)-Glyceraldehyde (–)-Glyceraldehyde(–)-Glyceraldehyde

The AldotetrosesThe Aldotetroses

stereochemistry assigned on basis of whetherstereochemistry assigned on basis of whether

configuration of highest-numbered stereogenic centerconfiguration of highest-numbered stereogenic center

is analogous to is analogous to DD or or LL-glyceraldehyde-glyceraldehyde

An AldotetroseAn Aldotetrose

CHCH OO

CHCH22OHOH

HH OHOH

HH OHOH

11

22

33

44


stereochemistry assigned on basis of whetherstereochemistry assigned on basis of whether

configuration of highest-numbered stereogenic centerconfiguration of highest-numbered stereogenic center

is analogous to is analogous to DD or or LL-glyceraldehyde-glyceraldehyde


CHCH OO

CHCH22OHOH

HH OHOH

HH OHOH

11

22

33

44DD



CHCH OO

CHCH22OHOH

HH OHOH

HH OHOH

11

22

33

44

DD-Erythrose-Erythrose


The Four AldotetrosesThe Four Aldotetroses

CHCH OO

CHCH22OHOH

HH OHOH

HH OHOH

CHCH OO

CHCH22OHOH

HHHOHO

HH OHOH

HH OHOH

CHCH OO

CHCH22OHOH

HHHOHO

DD-Erythrose-Erythrose LL-Erythrose-Erythrose DD-Threose-Threose LL-Threose-Threose

CHCH OO

CHCH22OHOH

HOHO HH

HHHOHO


Aldopentoses and AldohexosesAldopentoses and Aldohexoses

The AldopentosesThe Aldopentoses

There are 8 aldopentoses.There are 8 aldopentoses.

Four belong to the Four belong to the DD-series; four belong to -series; four belong to the the LL-series.-series.

Their names are ribose, arabinose, xylose, Their names are ribose, arabinose, xylose, and lyxose.and lyxose.

The Four The Four DD-Aldopentoses-Aldopentoses

DD-Ribose-Ribose

CHCH OO

CHCH22OHOH

HH OHOH

HH OHOH

HH OHOH

DD-Arabinose-Arabinose DD-Xylose-Xylose DD-Lyxose-Lyxose

HOHO

CHCH22OHOH

HH OHOH

HH OHOH

HH

CHCH OO

HOHO

HH OHOH

HH OHOH

HH

CHCH OO

CHCH22OHOH

HH OHOH

HH

HHHOHO

HOHO

CHCH OO

CHCH22OHOH


AldohexosesAldohexoses

There are 16 aldopentoses.There are 16 aldopentoses.

8 belong to the 8 belong to the DD-series; 8 belong to the -series; 8 belong to the LL--series.series.

Their names and configurations are best Their names and configurations are best remembered with the aid of the mnemonic remembered with the aid of the mnemonic described in Section 25.5.described in Section 25.5.

LL-Aldohexoses-Aldohexoses

There are 8 There are 8 aldohexoses of aldohexoses of the the LL-series.-series.

They have the They have the same name as same name as their mirror image their mirror image except the prefix is except the prefix is LL- rather than - rather than DD-.-.

CHCH OO

CHCH22OHOH

HH OHOH

HH OHOH

HH

HH OHOH

HOHO

DD-(+)-Glucose-(+)-Glucose LL-(–)-Glucose-(–)-Glucose

CHCH OO

CHCH22OHOH

HH

HH

HH

HH

OHOH

HOHO

HOHO

HOHO


Cyclic Forms of Carbohydrates:Cyclic Forms of Carbohydrates:

Furanose FormsFuranose Forms

RecallRecall

R"OR"OHHCC••••OO ••••

RR

R'R'

R"OR"O CC OO HH••••

••••

••••

••••

RR

R'R'

Product is a hemiacetal.Product is a hemiacetal.

++

equilibrium lies far to the rightequilibrium lies far to the right

cyclic hemiacetals that have 5-membered ringscyclic hemiacetals that have 5-membered ringsare called are called furanosefuranose forms forms

Carbohydrates Form Cyclic HemiacetalsCarbohydrates Form Cyclic Hemiacetals

CHCH OO

CHCH22OOHH

11

22

33

44

HH

OHOHOO

11

2233

44

stereochemistry is maintained during cyclicstereochemistry is maintained during cyclichemiacetal formationhemiacetal formation

DD-Erythrose-Erythrose

CHCH OO

CHCH22OOHH

11

22

33

44

HH

OHOHOO

11

2233

44

HH

HH

OHOH

OHOH

HH HH HH

OHOHOHOHHH

DD-Ribose-Ribose

CHCH OO

CHCH22OHOH

HH OOHH

HH OHOH

HH OHOH

11

22

33

44

55

furanose ring formation involves furanose ring formation involves OOH group at C-4H group at C-4

DD-Ribose-Ribose

CHCH OO

CHCH22OHOH

HH OOHH

HH OHOH

HH OHOH

11

22

33

44

55

need C(3)-C(4) bond rotation to put need C(3)-C(4) bond rotation to put OOH in proper H in proper orientation to close 5-membered ringorientation to close 5-membered ring

CHCH OOHHHH

HH CHCH22OHOH

OHOHOHOHHHOO

11

2233

44

55


DD-Ribose-Ribose CHCH OOHHHH

HH CHCH22OHOH

OHOHOHOHHHOO

11

2233

44

55 CHCH OOHHHH

HH

HOCHHOCH22

OHOHOHOH

OOHH11

2233

44

55


DD-Ribose-Ribose

CHCH22OH group becomes a substituent on ringOH group becomes a substituent on ring

CHCH OOHHHH

HH

HOCHHOCH22

OHOHOHOH

OOHH11

2233

44

55


DD-Ribose-Ribose

CHCH22OH group becomes a substituent on ringOH group becomes a substituent on ring

CHCH OOHHHH

HH

HOCHHOCH22

OHOHOHOH

OOHH11

2233

44

55 HOCHHOCH22

HH

OHOHOO

11

2233

44

HH HH

OHOHOHOHHH

55

--DD-Ribofuranose-Ribofuranose

Cyclic Forms of Carbohydrates:Cyclic Forms of Carbohydrates:

Pyranose FormsPyranose Forms

cyclic hemiacetals that have 6-membered ringscyclic hemiacetals that have 6-membered ringsare called are called pyranosepyranose forms forms

Carbohydrates Form Cyclic HemiacetalsCarbohydrates Form Cyclic Hemiacetals

HH

OHOHOO11

2233

44

55

CHCH OO

CHCH22OOHH

11

22

33

44

55

DD-Ribose-Ribose

CHCH OO

CHCH22OOHH

11

22

33

44

55

HH

HH

HH OHOH

OHOH

OHOH

pyranose ring formation involves pyranose ring formation involves OOH group at C-5H group at C-5



HH CHCH22OOHH

OHOHOHOHHOHO

11

2233

44

55CHCH OO

CHCH22OOHH

11

22

33

44

55

HH

HH

HH OHOH

OHOH

OHOH




HH CHCH22OOHH

OHOHOHOHHOHO

11

2233

44

55




HH CHCH22OOHH

OHOHOHOHHOHO

11

2233

44

55 HH

OHOHOO11

2233

44

OHOHOHOHHOHO

HHHH

HHHH

HH55

-D-D-Ribopyranose-Ribopyranose


DD-Glucose-Glucose

CHCH OO

CHCH22OHOH

11

22

33

44

55

HH

HOHO

HH OHOH

HH

OHOH

HH OOHH66


DD-Glucose-Glucose CHCH OOHHOHOH

HH

HOCHHOCH22

OHOHHHHOHO

11

2233

44

55

66

HHOOHH

-D-D-Glucopyranose-Glucopyranose

HH

OHOHOO11

2233

44

OHOHHHHOHO

HHOHOH

HHHH

HOCHHOCH22

55

66


DD-Glucose-Glucose


HH

OHOHOO11

2233

44

OHOHHHHOHO

HHOHOH

HHHH

HOCHHOCH22

55

66


OHOH

HHOO11

2233

44

OHOHHHHOHO

HHOHOH

HHHH

HOCHHOCH22

55

66


DD-Glucose-Glucose


OHOH

HHOHOH

HH

HOHOHOHO

HH

HHHH

HOCHHOCH22

OO

OH group at anomeric carbon is axialOH group at anomeric carbon is axialin in --DD-glucopyranose-glucopyranose

11


HH

OHOHOHOH

HH

HOHOHOHO

HH

HHHH

HOCHHOCH22

OO

11


KetosesKetoses

KetosesKetoses

Ketoses are carbohydrates that have a ketone Ketoses are carbohydrates that have a ketone carbonyl group in their open-chain form.carbonyl group in their open-chain form.

C-2 is usually the carbonyl carbon.C-2 is usually the carbonyl carbon.

ExamplesExamples

DD-Ribulose-Ribulose LL-Xyulose-Xyulose DD-Fructose-Fructose

HOHO

HH

CHCH22OHOH

CHCH22OHOH

OO

HH

OHOH

HH

HH

CHCH22OHOH

CHCH22OHOH

OO

OHOH

OHOH HOHO

HH

CHCH22OHOH

CHCH22OHOH

OO

OHOH

HH

HH OHOH

Deoxy SugarsDeoxy Sugars

Deoxy SugarsDeoxy Sugars

Often one or more of the carbons of a Often one or more of the carbons of a carbohydrate will lack an oxygen substituent. carbohydrate will lack an oxygen substituent. Such compounds are called deoxy sugars.Such compounds are called deoxy sugars.

2-Deoxy-2-Deoxy-DD-ribose-ribose

ExamplesExamples

CHCH OO

CHCH22OHOH

HH OHOH

HH OHOH

HH HH

6-Deoxy-6-Deoxy-LL-mannose-mannose

CHCH OO

CCHH33

HOHO HH

HH OHOH

HH OHOH

HOHO HH

Amino SugarsAmino Sugars

Amino SugarsAmino Sugars

An amino sugar has one or more of its oxygens An amino sugar has one or more of its oxygens replaced by nitrogen.replaced by nitrogen.

ExampleExample

NN-Acetyl--Acetyl-DD-glucosamine-glucosamine

OO

OHOH

NNHH

HOHOHOHO

HOCHHOCH22

CC

CHCH33

OO

ExampleExample

LL-Daunosamine-Daunosamine

OO

OHOH

HOHO

HH33CC

NNHH22

Branched-Chain CarbohydratesBranched-Chain Carbohydrates

Branched-Chain CarbohydratesBranched-Chain Carbohydrates

Carbohydrates that don't have a continuous Carbohydrates that don't have a continuous chain of carbon-carbon bonds are called chain of carbon-carbon bonds are called branched-chain carbohydrates.branched-chain carbohydrates.

ExamplesExamples

CHCH OO

CHCH22OHOH

HH OHOH

HOHO CHCH22OHOH

DD-Apiose-Apiose

OO

OHOH

HOHO

HH33CC

NHNH22

CHCH33

LL-Vancosamine-Vancosamine

GlycosidesGlycosides

GlycosidesGlycosides

Glycosides have a substituent other than OH at Glycosides have a substituent other than OH at the anomeric carbon.the anomeric carbon.

Usually the atom connected to the anomeric Usually the atom connected to the anomeric carbon is oxygen.carbon is oxygen.

ExampleExample

Linamarin is an Linamarin is an OO-glycoside -glycoside derived from derived from DD-glucose.-glucose.

OO

OHOH

OHOH

HOHOHOHO

HOCHHOCH22 OO

OOCCCC

OHOH

HOHOHOHO

HOCHHOCH22 CHCH33

NN

CHCH33

DD-Glucose-Glucose

DisaccharidesDisaccharides

DisaccharidesDisaccharides

Disaccharides are glycosides.Disaccharides are glycosides.

The glycosidic linkage connects two The glycosidic linkage connects two monosaccharides.monosaccharides.

Two structurally related disaccharides are Two structurally related disaccharides are cellobiose and maltose. Both are derived cellobiose and maltose. Both are derived from glucose.from glucose.

Maltose and CellobioseMaltose and Cellobiose

MaltoseMaltose

MaltoseMaltose is composed of two glucose units linked is composed of two glucose units linked together by a glycosidic bond between C-1 of together by a glycosidic bond between C-1 of one glucose and C-4 of the other.one glucose and C-4 of the other.

The stereochemistry at the anomeric carbon of The stereochemistry at the anomeric carbon of the glycosidic linkage is the glycosidic linkage is ..

The glycosidic linkage is described as The glycosidic linkage is described as (1,4)(1,4)

OO

HOCHHOCH22 HOCHHOCH22

OHOH

OHOHHOHOOHOHHOHO

HOHOOO OO11 44

Maltose and CellobioseMaltose and Cellobiose

CellobioseCellobiose

CellobioseCellobiose is a stereoisomer of maltose. is a stereoisomer of maltose.

The only difference between the two is that The only difference between the two is that cellobiose has a cellobiose has a (1,4) glycosidic bond while (1,4) glycosidic bond while that of maltose isthat of maltose is (1,4).(1,4).

OO


OHOH

OHOHHOHOOHOHHOHO

HOHOOO OO11 44

Maltose and Cellobiose

Cellobiose

Maltose


Cellobiose and LactoseCellobiose and Lactose

CellobioseCellobiose

CellobioseCellobiose and and lactoselactose are stereoisomeric are stereoisomeric disaccharides.disaccharides.

Both have Both have (1,4) glycosidic bonds.(1,4) glycosidic bonds.

The glycosidic bond unites two glucose units in The glycosidic bond unites two glucose units in cellobiose. It unites galactose and glucose in cellobiose. It unites galactose and glucose in lactose.lactose.

OO


OHOH

OHOHHOHOOHOHHOHO

HOHOOO OO11 44

Cellobiose and LactoseCellobiose and Lactose

LactoseLactose

CellobioseCellobiose and and lactoselactose are stereoisomeric are stereoisomeric disaccharides.disaccharides.

Both have Both have (1,4) glycosidic bonds.(1,4) glycosidic bonds.

The glycosidic bond unites two glucose units in The glycosidic bond unites two glucose units in cellobiose. It unites galactose and glucose in cellobiose. It unites galactose and glucose in lactose.lactose.

OO


OHOH

OHOHHOHOOHOHHOHO

HOHOOO OO11 44

PolysaccharidesPolysaccharides

CelluloseCellulose

Cellulose is a polysaccharide composed of Cellulose is a polysaccharide composed of several thousand several thousand DD-glucose units joined by -glucose units joined by (1,4)-glycosidic linkages. Thus, it can also (1,4)-glycosidic linkages. Thus, it can also be viewed as a repeating collection of be viewed as a repeating collection of cellobiose units.cellobiose units.

Cellulose

Four glucose units of a cellulose chain.

StarchStarch

Starch is a mixture of amylose and amylopectin. Starch is a mixture of amylose and amylopectin.

Amylose is a polysaccharide composed of 100 Amylose is a polysaccharide composed of 100 to several thousand to several thousand DD-glucose units joined by -glucose units joined by (1,4)-glycosidic linkages.(1,4)-glycosidic linkages.

Lecture 24- Carbohydrates

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