dr. wolf's chm 424 25- 1 modified chapter 25 carbohydrates

Dr. Wolf's CHM 424 25- 1

ModifiedModifiedChapter 25Chapter 25

CarbohydratesCarbohydrates


25.125.1Classification 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)

CC66HH1212OO6 6 + + CC66HH1212OO66

glucoseglucose(a monosaccharide)(a monosaccharide)

fructosefructose(a monosaccharide)(a monosaccharide)


oligosaccharideoligosaccharide::

gives two or more monosaccharide units on gives two or more monosaccharide units on hydrolysishydrolysis

is homogeneous—all molecules of a particularis homogeneous—all molecules of a particularoligosaccharide are the same, including chainoligosaccharide are the same, including chainlengthlength

polysaccharidepolysaccharide: :

yields "many" monosaccharide units on hydrolysisyields "many" monosaccharide units on hydrolysis

mixtures of the same polysaccharide differing onlymixtures of the same polysaccharide differing onlyin chain lengthin chain length

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

Table 25.1 Some Classes of CarbohydratesTable 25.1 Some Classes of Carbohydrates


25.225.2Fischer 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


25.325.3The 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

44DD


An AldotetroseAn Aldotetrose

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

DD-Erythrose-Erythrose LL-Erythrose-Erythrose

CHCH OO

CHCH22OHOH

HOHO HH

HHHOHO

DD-Erythrose and -Erythrose and LL-erythrose are -erythrose are enantiomersenantiomers



CHCH OO

CHCH22OHOH

HH OHOH

HH OHOH

CHCH OO

CHCH22OHOH

HHHOHO

HH OHOH

DD-Erythrose-Erythrose DD-Threose-Threose

DD-Erythrose and -Erythrose and DD-threose are -threose are diastereomersdiastereomers


CHCH OO

CHCH22OHOH

HOHO HH

HHHOHO


CHCH OO

CHCH22OHOH

HHHOHO

HH OHOH

LL-Erythrose-Erythrose DD-Threose-Threose

LL-Erythrose and -Erythrose and DD-threose are -threose are diastereomersdiastereomers



CHCH OO

CHCH22OHOH

HHHOHO

HH OHOH

DD-Threose-Threose

DD-Threose and -Threose and LL-threose are -threose are enantiomersenantiomers

LL-Threose-Threose

OHOH

CHCH OO

CHCH22OHOH

HHHOHO

HH



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


25.425.4Aldopentoses 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 DD-Arabinose-Arabinose DD-Xylose-Xylose DD-Lyxose-Lyxose

HH OHOH HOHO HH HH OHOH HHHOHO

HH OHOH HH OHOH HOHO HH HHHOHO

CHCH22OHOH

HH OHOH HH OHOH HH OHOH HH OHOH

CHCH OO

CHCH22OHOH

CHCH OO CHCH OO

CHCH22OHOH

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.


25.525.5A Mnemonic for Carbohydrate A Mnemonic for Carbohydrate

ConfigurationsConfigurations


The Eight The Eight DD-Aldohexoses-Aldohexoses

CHCH OO

CHCH22OHOH

HH OHOH


AllAll

AltruistsAltruists

GladlyGladly

MakeMake

GumGum

InIn

GallonGallon

TanksTanks


CHCH OO

CHCH22OHOH

HH OHOH


AllAll AlloseAllose

AltruistsAltruists AltroseAltrose

GladlyGladly GlucoseGlucose

MakeMake MannoseMannose

GumGum GuloseGulose

InIn IdoseIdose

GallonGallon GalactoseGalactose

TanksTanks TaloseTalose


CHCH OO

CHCH22OHOH

HH OHOH


AlloseAllose

AltroseAltrose

GlucoseGlucose

MannoseMannose

GuloseGulose

IdoseIdose

GalactoseGalactose

TaloseTalose


CHCH OO

CHCH22OHOH

HH OHOH


AlloseAllose

AltroseAltrose

GlucoseGlucose

MannoseMannose

GuloseGulose

IdoseIdose

GalactoseGalactose

TaloseTalose


CHCH OO

CHCH22OHOH

HH OHOH

HH OHOH


AlloseAllose

AltroseAltrose

GlucoseGlucose

MannoseMannose

GuloseGulose

IdoseIdose

GalactoseGalactose

TaloseTalose


CHCH OO

CHCH22OHOH

HH OHOH

HHHOHO


AlloseAllose

AltroseAltrose

GlucoseGlucose

MannoseMannose

GuloseGulose

IdoseIdose

GalactoseGalactose

TaloseTalose


CHCH OO

CHCH22OHOH

HH OHOH

HH OHOH


AlloseAllose

AltroseAltrose

GlucoseGlucose

MannoseMannose

GuloseGulose

IdoseIdose

GalactoseGalactose

TaloseTalose


CHCH OO

CHCH22OHOH

HH OHOH

HH OHOH

HH OHOH


AlloseAllose

AltroseAltrose

GlucoseGlucose

MannoseMannose

GuloseGulose

IdoseIdose

GalactoseGalactose

TaloseTalose


CHCH OO

CHCH22OHOH

HH OHOH

HH OHOH

HHHOHO


AlloseAllose

AltroseAltrose

GlucoseGlucose

MannoseMannose

GuloseGulose

IdoseIdose

GalactoseGalactose

TaloseTalose


CHCH OO

CHCH22OHOH

HH OHOH

HHHOHO


AlloseAllose

AltroseAltrose

GlucoseGlucose

MannoseMannose

GuloseGulose

IdoseIdose

GalactoseGalactose

TaloseTalose


CHCH OO

CHCH22OHOH

HH OHOH

HHHOHO

HH OHOH


AlloseAllose

AltroseAltrose

GlucoseGlucose

MannoseMannose

GuloseGulose

IdoseIdose

GalactoseGalactose

TaloseTalose


CHCH OO

CHCH22OHOH

HH OHOH

HHHOHO

HHHOHO


AlloseAllose

AltroseAltrose

GlucoseGlucose

MannoseMannose

GuloseGulose

IdoseIdose

GalactoseGalactose

TaloseTalose


CHCH OO

CHCH22OHOH

HH OHOH

HH OHOH

HH OHOH


AlloseAllose

AltroseAltrose

GlucoseGlucose

MannoseMannose

GuloseGulose

IdoseIdose

GalactoseGalactose

TaloseTalose


CHCH OO

CHCH22OHOH

HH OHOH

HH OHOH

HH OHOH

HH OHOH


AlloseAllose

AltroseAltrose

GlucoseGlucose

MannoseMannose

GuloseGulose

IdoseIdose

GalactoseGalactose

TaloseTalose


CHCH OO

CHCH22OHOH

HH OHOH

HH OHOH

HH OHOH

HHHOHO


AlloseAllose

AltroseAltrose

GlucoseGlucose

MannoseMannose

GuloseGulose

IdoseIdose

GalactoseGalactose

TaloseTalose


HOHO

CHCH OO

CHCH22OHOH

HH OHOH

HH OHOH

HH


AlloseAllose

AltroseAltrose

GlucoseGlucose

MannoseMannose

GuloseGulose

IdoseIdose

GalactoseGalactose

TaloseTalose


HOHO

CHCH OO

CHCH22OHOH

HH OHOH

HH OHOH

HH

HH OHOH


AlloseAllose

AltroseAltrose

GlucoseGlucose

MannoseMannose

GuloseGulose

IdoseIdose

GalactoseGalactose

TaloseTalose


HOHO

CHCH OO

CHCH22OHOH

HH OHOH

HH OHOH

HH

HHHOHO


AlloseAllose

AltroseAltrose

GlucoseGlucose

MannoseMannose

GuloseGulose

IdoseIdose

GalactoseGalactose

TaloseTalose


CHCH OO

CHCH22OHOH

HH OHOH

HHHOHO

HH OHOH


AlloseAllose

AltroseAltrose

GlucoseGlucose

MannoseMannose

GuloseGulose

IdoseIdose

GalactoseGalactose

TaloseTalose


CHCH OO

CHCH22OHOH

HH OHOH

HHHOHO

HH OHOH

HH OHOH


AlloseAllose

AltroseAltrose

GlucoseGlucose

MannoseMannose

GuloseGulose

IdoseIdose

GalactoseGalactose

TaloseTalose


CHCH OO

CHCH22OHOH

HH OHOH

HHHOHO

HH OHOH

HHHOHO


AlloseAllose

AltroseAltrose

GlucoseGlucose

MannoseMannose

GuloseGulose

IdoseIdose

GalactoseGalactose

TaloseTalose


CHCH OO

CHCH22OHOH

HH OHOH

HHHOHO

HHHOHO


AlloseAllose

AltroseAltrose

GlucoseGlucose

MannoseMannose

GuloseGulose

IdoseIdose

GalactoseGalactose

TaloseTalose


CHCH OO

CHCH22OHOH

HH OHOH

HHHOHO

HHHOHO

HH OHOH


AlloseAllose

AltroseAltrose

GlucoseGlucose

MannoseMannose

GuloseGulose

IdoseIdose

GalactoseGalactose

TaloseTalose


CHCH OO

CHCH22OHOH

HH OHOH

HHHOHO

HHHOHO

HHHOHO


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


25.625.6

Cyclic Forms of Carbohydrates:Cyclic Forms of Carbohydrates:

Furanose FormsFuranose Forms


Recall from Section 17.8Recall from Section 17.8

R"OR"OHHCC••••OO ••••

RR

R'R'

R"OR"O CC OO HH••••

••••

••••

••••

RR

R'R'

Product is a hemiacetal.Product is a hemiacetal.

++


Cyclic HemiacetalsCyclic Hemiacetals

Aldehydes and ketones that contain an Aldehydes and ketones that contain an OOH H group elsewhere in the molecule can undergo group elsewhere in the molecule can undergo intramolecular hemiacetal formation.intramolecular hemiacetal formation.

The equilibrium favors the cyclic hemiacetal if The equilibrium favors the cyclic hemiacetal if the ring is 5- or 6-membered.the ring is 5- or 6-membered.

CC OO

RR

OOHH

CC

OHOHRR

OO


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


CHCH OO

CHCH22OOHH

11

22

33

44

HH

OHOHOO

11

2233

44

HH

HH

OHOH

OHOH

HH HH HH

OHOHOHOHHH


D-Erythrose

turn 90°

1

23

4

1

2

3

4


D-Erythrose

move O into position by rotating about bond between carbon-3 and carbon-4

1

23

4


D-Erythrose

1

23

41

23

4


D-Erythrose

1

23

4close ring by hemiacetal formation between OH at C-4 and carbonyl group


D-Erythrose

1

23

41

23

4


stereochemistry is variable at anomeric carbon;stereochemistry is variable at anomeric carbon;two diastereomers are formedtwo diastereomers are formed


CHCH OO

CHCH22OOHH

11

22

33

44

HH

OHOHOO

11

2233

44

HH

HH

OHOH

OHOH

HH HH HH

OHOHOHOHHH

anomeric carbonanomeric carbon


DD-Erythrose-Erythrose HH

OHOHOO

11

2233

44

HH HH HH

OHOHOHOHHH

OHOH

HHOO

11

2233

44

HH HH HH

OHOHOHOHHH

--DD-Erythrofuranose-Erythrofuranose --DD-Erythrofuranose-Erythrofuranose


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 HOCHHOCH22

HH

OHOHOO

11

2233

44

HH HH

OHOHOHOHHH

55

--DD-Ribofuranose-Ribofuranose


25.725.7

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

CHCH OOHHHH

HH CHCH22OOHH

OHOHOHOHHOHO

11

2233

44

55

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


DD-Ribose-Ribose CHCH OOHHHH

HH CHCH22OOHH

OHOHOHOHHOHO

11

2233

44

55 HH

OHOHOO11

2233

44

OHOHOHOHHOHO

HHHH

HHHH

HH55

-D-D-Ribopyranose-Ribopyranose


DD-Ribose-Ribose HH

OHOHOO11

2233

44

OHOHOHOHHOHO

HHHH

HHHH

HH55


OHOH

HHOO11

2233

44

OHOHOHOHHOHO

HHHH

HHHH

HH55



DD-Glucose-Glucose

CHCH OO

CHCH22OHOH

11

22

33

44

55

HH

HOHO

HH OHOH

HH

OHOH

HH OOHH66

OOHH

CHCH OOHHOHOH

HH CHCH22OHOH

OHOHHHHOHO

11

2233

44

5566

HH

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


DD-Glucose-Glucose CHCH OOHHOHOH

HH CHCH22OHOH

OHOHHHHOHO

11

2233

44

5566

HH

OOHH

CHCH OOHHOHOH

HH

HOCHHOCH22

OHOHHHHOHO

11

2233

44

55

66

HHOOHH

need C(4)-C(5) bond rotation to put need C(4)-C(5) bond rotation to put OOH in proper H in proper orientation to close 6-membered ringorientation to close 6-membered ring


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


HH

OHOHOO11

2233

44

OHOHHHHOHO

HHOHOH

HHHH

HOCHHOCH22

55

66

pyranose forms of carbohydrates adopt chair pyranose forms of carbohydrates adopt chair conformationsconformations


DD-Glucose-Glucose


HH

OHOHOO11

2233

44

OHOHHHHOHO

HHOHOH

HHHH

HOCHHOCH22

55

66 OHOH

HHOHOH

HH

HOHOHOHO

HH

HHHH

HOCHHOCH22

OO

all substituents are equatorial in all substituents are equatorial in --DD-glucopyranose-glucopyranose

112233

4455

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


Figure 25.5Figure 25.5

CHCH OO

CHCH22OHOH

HH OOHH

HH OHOH

HH OHOH

Less than 1% of the open-chain form of Less than 1% of the open-chain form of DD-ribose -ribose is present at equilibrium in aqueous solution.is present at equilibrium in aqueous solution.


Figure 25.5Figure 25.5 OHOH

HHOHOH

HH

HHHOHO

HH

OHOHHH

OO

-D-D-Ribopyranose (56%)-Ribopyranose (56%)

HH

HOHO

-D-D-Ribopyranose (20%)-Ribopyranose (20%)

HH

OHOHOHOH

HH

HH

HH

OHOHHH

OO

11

HH

76% of the 76% of the DD-ribose is a mixture of the -ribose is a mixture of the and and - - pyranose forms, with the pyranose forms, with the -form predominating-form predominating


Figure 25.5Figure 25.5 HOCHHOCH22

HH

OHOHOOHH HH

OHOHOHOHHH

--DD-Ribofuranose (18%)-Ribofuranose (18%)

HOCHHOCH22

OHOH

HHOOHH HH

OHOHOHOHHH

--DD-Ribofuranose (6%)-Ribofuranose (6%)

The The and and -furanose forms comprise 24% of -furanose forms comprise 24% of the mixture.the mixture.


25.825.8MutarotationMutarotation


MutarotationMutarotation

Mutarotation is a term given to the change in Mutarotation is a term given to the change in the observed optical rotation of a substance with the observed optical rotation of a substance with time. time.

Glucose, for example, can be obtained in Glucose, for example, can be obtained in either its either its or or -pyranose form. The two forms -pyranose form. The two forms have different physical properties such as have different physical properties such as melting point and optical rotation.melting point and optical rotation.

When either form is dissolved in water, its When either form is dissolved in water, its initial rotation changes with time. Eventually initial rotation changes with time. Eventually both solutions have the same rotation.both solutions have the same rotation.


Mutarotation of Mutarotation of D D-Glucose-Glucose


OHOH

HHOHOH

HH

HOHOHOHO

HH

HHHH

HOCHHOCH22

OO

11


HH

OHOHOHOH

HH

HOHOHOHO

HH

HHHH

HOCHHOCH22

OO

11

Initial: [Initial: []]DD +18.7° +18.7° Initial: [Initial: []]DD +112.2° +112.2°

Final: [Final: []]DD +52.5° +52.5°


Mutarotation of Mutarotation of D D-Glucose-Glucose


OHOH

HHOHOH

HH

HOHOHOHO

HH

HHHH

HOCHHOCH22

OO

11


HH

OHOHOHOH

HH

HOHOHOHO

HH

HHHH

HOCHHOCH22

OO

11

Explanation: After being dissolved in water, the Explanation: After being dissolved in water, the and and forms slowly interconvert via the open- forms slowly interconvert via the open-chain form. An equilibrium state is reached that chain form. An equilibrium state is reached that contains 64% contains 64% and 36% and 36% . .


25.925.9KetosesKetoses


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


25.1325.13GlycosidesGlycosides


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 Linamarin is an 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



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.

Examples of glycosides in which the atom Examples of glycosides in which the atom connected to the anomeric carbon is something connected to the anomeric carbon is something other than oxygen include other than oxygen include SS-glycosides and -glycosides and NN--glycosides.glycosides.


ExampleExample

Adenosine is an Adenosine is an NN--glycoside derived from glycoside derived from DD-ribose-ribose HOCHHOCH22

HH

OHOHOOHH HH

OHOHOHOHHH

DD-Ribose-Ribose

HOCHHOCH22

HH

NNOOHH HH

OHOHOHOHHH

NN

NHNH22

NN

NN

AdenosineAdenosine


ExampleExample

Sinigrin is an Sinigrin is an SS-glycoside -glycoside derived from derived from DD-glucose.-glucose.

OO

OHOH

OHOH

HOHOHOHO

HOCHHOCH22

DD-Glucose-Glucose OO

SSCCHCCH22CHCH

OHOH

HOHOHOHO

HOCHHOCH22

CHCH22

NOSONOSO33KK



OO-Glycosides are mixed acetals-Glycosides are mixed acetals..


O-Glycosides are mixed acetalsO-Glycosides are mixed acetals HH

OHOHOO

CHCH OO

CHCH22OOHH

hemiacetalhemiacetal HH

OROROOROHROH

acetalacetal


Preparation of GlycosidesPreparation of Glycosides

Glycosides of simple alcohols (such as Glycosides of simple alcohols (such as methanol) are prepared by adding an acid methanol) are prepared by adding an acid catalyst (usually gaseous HCl) to a solution of a catalyst (usually gaseous HCl) to a solution of a carbohydrate in the appropriate alcohol.carbohydrate in the appropriate alcohol.

Only the anomeric OH group is replaced.Only the anomeric OH group is replaced.

An equilibrium is established between the An equilibrium is established between the and and -glycosides (thermodynamic control). The -glycosides (thermodynamic control). The more stable stereoisomer predominates.more stable stereoisomer predominates.


Preparation of GlycosidesPreparation of Glycosides

HOHO

CHCH OO

CHCH22OHOH

HH OHOH

HH OHOH

HH

HH OHOHCHCH33OHOH

HClHCl

DD-Glucose-Glucose

OO

OCHOCH33

OHOH

HOHOHOHO

HOCHHOCH22

++ OO

OCHOCH33

OHOH

HOHOHOHO

HOCHHOCH22


Preparation of GlycosidesPreparation of Glycosides OO

OCHOCH33

OHOH

HOHOHOHO

HOCHHOCH22

++ OO

OCHOCH33

OHOH

HOHOHOHO

HOCHHOCH22

MethylMethyl--DD-glucopyranoside-glucopyranoside

MethylMethyl--DD-glucopyranoside-glucopyranoside

(major product)(major product)

Dr. Wolf's CHM 424 25- 100

Mechanism of Glycoside FormationMechanism of Glycoside Formation

HClHCl

carbocation is stabilized carbocation is stabilized by lone-pair donation from by lone-pair donation from oxygen of the ringoxygen of the ring

OO

OHOH

OHOH

HOHOHOHO

HOCHHOCH22••••

•••• OO

OHOH

HOHOHOHO

HOCHHOCH22

++

HH

•••• ••••

Dr. Wolf's CHM 424 25- 101

Mechanism of Glycoside FormationMechanism of Glycoside Formation

OO

OHOH

HOHOHOHO

HOCHHOCH22

++

HH

•••• •••• OO••••

HH

CHCH33

••••

OO

OO

OHOH

HOHOHOHO

HOCHHOCH22 •••• ••••CHCH33

HH

••••++

++

OO

OHOH

HOHOHOHO

HOCHHOCH22

OOHHHH33CC ••••

++

Dr. Wolf's CHM 424 25- 102

Mechanism of Glycoside FormationMechanism of Glycoside Formation OO

OO

OHOH

HOHOHOHO

HOCHHOCH22 •••• ••••CHCH33

HH

••••++

++

OO

OHOH

HOHOHOHO

HOCHHOCH22

OOHHHH33CC ••••

++

++

••••

OO

OCHOCH33

OHOH

HOHOHOHO

HOCHHOCH22 •••• ••••

••••

––HH++

••••OO

OCHOCH33

OHOH

HOHOHOHO

HOCHHOCH22

••••

••••

••••

Dr. Wolf's CHM 424 25- 103

25.1425.14DisaccharidesDisaccharides

Dr. Wolf's CHM 424 25- 104

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 from cellobiose and maltose. Both are derived from glucose.glucose.

Dr. Wolf's CHM 424 25- 105

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

Dr. Wolf's CHM 424 25- 106

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

Dr. Wolf's CHM 424 25- 107

Maltose and Cellobiose

CellobioseMaltose

Dr. Wolf's CHM 424 25- 108

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

Dr. Wolf's CHM 424 25- 109

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

Dr. Wolf's CHM 424 25- 110

25.1825.18Reduction of CarbohydratesReduction of Carbohydrates

Dr. Wolf's CHM 424 25- 111

Reduction of CarbohydratesReduction of Carbohydrates

Carbonyl group of open-chain form is reduced Carbonyl group of open-chain form is reduced to an alcohol.to an alcohol.

Product is called an alditol.Product is called an alditol.

Alditol lacks a carbonyl group so cannot cyclize Alditol lacks a carbonyl group so cannot cyclize to a hemiacetal.to a hemiacetal.

Dr. Wolf's CHM 424 25- 112

Reduction of Reduction of DD-Galactose-Galactose

--DD-galactofuranose-galactofuranose

--DD-galactofuranose-galactofuranose

--DD-galactopyranose-galactopyranose

--DD-galactopyranose-galactopyranose

CHCH22OHOH

HH OHOH

HHHOHO

HHHOHO

HH OHOH

CHCH OO

CHCH22OHOH

HH OHOH

HHHOHO

HHHOHO

HH OHOH

CHCH22OHOH

DD-Galactitol (90%)-Galactitol (90%)

reducing agent: NaBHreducing agent: NaBH44, H, H22OO

(catalytic hydrogenation can also be used)(catalytic hydrogenation can also be used)

Dr. Wolf's CHM 424 25- 113

25.1925.19Oxidation of CarbohydratesOxidation of Carbohydrates

Dr. Wolf's CHM 424 25- 114

Benedict's ReagentBenedict's Reagent

Benedict's reagent is a solution of the citrate complex of Benedict's reagent is a solution of the citrate complex of CuSOCuSO44 in water. It is used as a test for "reducing in water. It is used as a test for "reducing

sugars." Cusugars." Cu2+2+ is a weak oxidizing agent. is a weak oxidizing agent.

A reducing sugar is one which has an aldehyde function, A reducing sugar is one which has an aldehyde function, or is in equilibrium with one that does.or is in equilibrium with one that does.

A positive test is the formation of a red precipitate of A positive test is the formation of a red precipitate of CuCu22O.O.

++ 22CuCu2+2+RCHRCH

OO

5HO5HO––++ ++ CuCu22OORCORCO––

OO

3H3H22OO++

Dr. Wolf's CHM 424 25- 115

Examples of Reducing SugarsExamples of Reducing Sugars

Aldoses: because they have an aldehyde Aldoses: because they have an aldehyde function in their open-chain form.function in their open-chain form.

Ketoses: because enolization establishes an Ketoses: because enolization establishes an equilibrium with an aldose.equilibrium with an aldose.

CHCH22OHOH

CC OO

RR

CHOHCHOH

CC OHOH

RR

CHCH

CHOHCHOH

RR

OO

oxidized by oxidized by CuCu2+2+

Dr. Wolf's CHM 424 25- 116


Disaccharides that have a free hemiacetal Disaccharides that have a free hemiacetal function.function.

OO


OHOH

OHOHHOHOOHOHHOHO

HOHOOO OO

MaltoseMaltose

Dr. Wolf's CHM 424 25- 117


Disaccharides that have a free hemiacetal Disaccharides that have a free hemiacetal function.function.

oxidized by oxidized by CuCu2+2+

OO


OHOHHOHOOHOHHOHO

HOHOOO OHOH

CHCH OOMaltoseMaltose

Dr. Wolf's CHM 424 25- 118

Glycosides are not reducing sugarsGlycosides are not reducing sugars OO

OCHOCH33

OHOH

HOHOHOHO

HOCHHOCH22

Methyl Methyl --DD-glucopyranoside lacks a free-glucopyranoside lacks a freehemiacetal function; cannot be in equilibriumhemiacetal function; cannot be in equilibriumwith a species having an aldehyde functionwith a species having an aldehyde function

Dr. Wolf's CHM 424 25- 119

Oxidation of Reducing SugarsOxidation of Reducing Sugars

The compounds formed on oxidation of The compounds formed on oxidation of reducing sugars are called aldonic acids.reducing sugars are called aldonic acids.

Aldonic acids exist as lactones when 5- or 6-Aldonic acids exist as lactones when 5- or 6-membered rings can form.membered rings can form.

A standard method for preparing aldonic acids A standard method for preparing aldonic acids uses Bruses Br22 as the oxidizing agent. as the oxidizing agent.

Dr. Wolf's CHM 424 25- 120

Oxidation of Oxidation of DD-Xylose-Xylose

HOHO

HH OHOH

HH OHOH

HH

CHCH OO

CHCH22OHOH

BrBr22

HH22OO

DD-Xylose-Xylose

HOHO

HH OHOH

HH OHOH

HH

CHCH22OHOH

COCO22HH

DD-Xylonic acid (90%)-Xylonic acid (90%)

Dr. Wolf's CHM 424 25- 121

Oxidation of Oxidation of DD-Xylose-Xylose

HOHO

HH OOHH

HH OHOH

HH

CHCH22OOHH

COCO22HH

DD-Xylonic acid (90%)-Xylonic acid (90%)

OOOO

OHOH

OHOHHHOOCHCH22

OO

OO

OHOH

HOHOHHOO

++

Dr. Wolf's CHM 424 25- 122

Ruff Degradation Ruff Degradation Part 1,Oxidation of Part 1,Oxidation of DD-Glucose-Glucose

CHCH OO

CHCH22OHOH

HH OHOH

HH OHOH

HH

HH OHOH

HOHO

CHCH22OHOH

HH OHOH

HH OHOH

HH

HH OHOH

HOHO

COCO22HH

DD-Gluconic acid-Gluconic acidDD-Glucose-Glucose

BrBr22

HH22OO

Dr. Wolf's CHM 424 25- 123

Ruff Degradation Ruff Degradation Part 2,Oxidized Carbon RemovedPart 2,Oxidized Carbon Removed

CHCH22OHOH

HH OHOH

HH OHOH

HH

HH OHOH

HOHO

COCO22HH

DD-Gluconic acid-Gluconic acid

1) CaCO1) CaCO33

2) H2) H22OO22, Fe, Fe+3+3 HH

HH OHOH

HH

OHOH

CHCH OO

CHCH22OHOH

HO

D-Arabinose

Dr. Wolf's CHM 424 25- 124

Nitric Acid OxidationNitric Acid Oxidation

Nitric acid oxidizes both the aldehyde function Nitric acid oxidizes both the aldehyde function and the terminal CHand the terminal CH22OH of an aldose to COOH of an aldose to CO22H.H.

The products of such oxidations are called The products of such oxidations are called aldaric acids.aldaric acids.

Dr. Wolf's CHM 424 25- 125

Nitric Acid OxidationNitric Acid Oxidation

CHCH OO

CHCH22OHOH

HH OHOH

HH OHOH

HH

HH OHOH

HOHO HNOHNO33

60°C60°C

COCO22HH

HH OHOH

HH OHOH

HH

HH OHOH

HOHO

COCO22HH

DD-Glucaric acid (41%)-Glucaric acid (41%)DD-Glucose-Glucose

Dr. Wolf's CHM 424 25- 126

25.2025.20Cyanohydrin Formation and Cyanohydrin Formation and

Carbohydrate Chain ExtensionCarbohydrate Chain ExtensionKiliani-Fischer SynthesisKiliani-Fischer Synthesis

Dr. Wolf's CHM 424 25- 127

Extending the Carbohydrate ChainExtending the Carbohydrate Chain

Carbohydrate chains can be extended by using Carbohydrate chains can be extended by using cyanohydrin formation as the key step in C—C cyanohydrin formation as the key step in C—C bond-making.bond-making.

The classical version of this method is called the The classical version of this method is called the Kiliani-Fischer synthesis. The following Kiliani-Fischer synthesis. The following example is a more modern modification.example is a more modern modification.

Dr. Wolf's CHM 424 25- 128

--LL-arabinofuranose-arabinofuranose

--LL-arabinofuranose-arabinofuranose

--LL-arabinopyranose-arabinopyranose

--LL-arabinopyranose-arabinopyranose

CHCH22OHOH

HHHOHO

HHHOHO

HH OHOH

CHCH OO


HCNHCN

CHCH22OHOH

HOHO HH

HHHOHO

OHOHHH

CNCN

CHCHOOHH

the cyanohydrin is a mixture of two stereoisomers that the cyanohydrin is a mixture of two stereoisomers that differ in configuration at C-2; these two diastereomers are differ in configuration at C-2; these two diastereomers are separated in the next stepseparated in the next step

Dr. Wolf's CHM 424 25- 129


CHCH22OHOH

HOHO HH

HHHOHO

OHOHHH

CNCN

CHCHOOHH

CHCH22OHOH

HOHO HH

HHHOHO

OHOHHH

HH OOHH

CNCN

CHCH22OHOH

HOHO HH

HHHOHO

OHOHHH

HHOO HH

CNCN

++separateseparate

LL-Mannononitrile-Mannononitrile LL-Gluconononitrile-Gluconononitrile

Dr. Wolf's CHM 424 25- 130


CHCH22OHOH

HOHO HH

HHHOHO

OHOHHH

HH OOHH

CNCN

LL-Mannononitrile-Mannononitrile

HH22, H, H22OO

Pd, BaSOPd, BaSO44

LL-Mannose-Mannose(56% from (56% from LL-arabinose)-arabinose)

CHCH22OHOH

HOHO HH

HHHOHO

OHOHHH

HH OOHH

CCHH OO

Dr. Wolf's CHM 424 25- 131

Likewise...Likewise...

CHCH22OHOH

HOHO HH

HHHOHO

OHOHHH

HHOO HH

CNCN

LL-Gluconononitrile-Gluconononitrile

HH22, H, H22OO

Pd, BaSOPd, BaSO44

LL-Glucose-Glucose(26% from (26% from LL-arabinose)-arabinose)

CHCH22OHOH

HOHO HH

HHHOHO

OHOHHH

HHOO HH

CCHH OO

Dr. Wolf's CHM 424 25- 132

25.2125.21Epimerization and Isomerization Epimerization and Isomerization

of Carbohydratesof Carbohydrates

Dr. Wolf's CHM 424 25- 133

Enol Forms of CarbohydratesEnol Forms of Carbohydrates

Enolization of an aldose scrambles the Enolization of an aldose scrambles the stereochemistry at C-2.stereochemistry at C-2.

This process is called This process is called epimerizationepimerization. . Diastereomers that differ in stereochemistry at Diastereomers that differ in stereochemistry at only one of their stereogenic centers are called only one of their stereogenic centers are called epimers.epimers.

DD-Glucose and -Glucose and DD-mannose, for example, are -mannose, for example, are epimers. epimers.

Dr. Wolf's CHM 424 25- 134

EpimerizationEpimerization

CHCH OO

CHCH22OHOH

HH OHOH

HH OHOH

HH

HH OHOH

HOHO

DD-Mannose-MannoseDD-Glucose-Glucose

CHCH OO

CHCH22OHOH

HH OHOH

HH OHOH

HH

HOHO HH

HOHO

EnediolEnediol

CHCH22OHOH

HH OHOH

HH OHOH

HH

OHOH

HOHO

CHOHCHOH

CC

This equilibration can be catalyzed by hydroxide ion.This equilibration can be catalyzed by hydroxide ion.

Dr. Wolf's CHM 424 25- 135

Enol Forms of CarbohydratesEnol Forms of Carbohydrates

The enediol intermediate on the preceding slide The enediol intermediate on the preceding slide can undergo a second reaction. It can lead to can undergo a second reaction. It can lead to the conversion of the conversion of DD-glucose or -glucose or DD-mannose -mannose (aldoses) to (aldoses) to DD-fructose (ketose).-fructose (ketose).

Dr. Wolf's CHM 424 25- 136

IsomerizationIsomerization

EnediolEnediol

CHCH22OHOH

HH OHOH

HH OHOH

HH

OHOH

HOHO

CHOHCHOH

CC

DD-Glucose or-Glucose orDD-Mannose-Mannose

CHCH OO

CHCH22OHOH

HH OHOH

HH OHOH

HHHOHO

CHOHCHOH

DD-Fructose-Fructose

CHCH22OHOH

CHCH22OHOH

HH OHOH

HH OHOH

HHHOHO

CC OO

Dr. Wolf's CHM 424 25- 137

25.2225.22Acylation and Alkylation of Acylation and Alkylation of

Hydroxyl Groups in Hydroxyl Groups in CarbohydratesCarbohydrates

Dr. Wolf's CHM 424 25- 138

Reactivity of Hydroxyl Groups in Reactivity of Hydroxyl Groups in CarbohydratesCarbohydrates

acylationacylationalkylationalkylation

Hydroxyl groups in carbohydrates undergo Hydroxyl groups in carbohydrates undergo reactions typical of alcohols.reactions typical of alcohols.

Dr. Wolf's CHM 424 25- 139

Example: Example: AcylationAcylation of of --DD-glucopyranose-glucopyranose OO

OHOHOHOH

HOHOHOHO

HOCHHOCH22

++ CHCH33COCCHCOCCH33

OO OO

55

pyridinepyridine OO

OO

CHCH33CCOCHOCH22

OO

CHCH33CCOO

OO

CHCH33CCOO

OOCHCH33CCOO

OOOOCCHCCH33

(88%)(88%)

Dr. Wolf's CHM 424 25- 140

Example: Example: AlkylationAlkylation of methyl of methyl --DD-glucopyranoside-glucopyranoside OO

OCHOCH33

OHOH

HOHOHOHO

HOCHHOCH22

++ 44CHCH33II

AgAg22O, CHO, CH33OHOH OO

OCHOCH33

CHCH33OO

CHCH33OOCHCH33OO

CHCH33OCHOCH22

(97%)(97%)

Dr. Wolf's CHM 424 25- 141

Classical Method for Ring SizeClassical Method for Ring Size

Ring sizes (furanose or pyranose) have been Ring sizes (furanose or pyranose) have been determined using alkylation as a key step.determined using alkylation as a key step.

OO

OCHOCH33

OHOH

HOHOHOHO

HOCHHOCH22

OCHOCH33

OO

CHCH33OO

CHCH33OOCHCH33OO

CHCH33OCHOCH22

Dr. Wolf's CHM 424 25- 142



OO

OCHOCH33

CHCH33OO

CHCH33OOCHCH33OO

CHCH33OCHOCH22

HH22OO

HH++

(mixture of (mixture of + + ))

OO

OHOHCHCH33OO

CHCH33OOCHCH33OO

CHCH33OCHOCH22

Dr. Wolf's CHM 424 25- 143



(mixture of (mixture of + + ))

OO

OHOHCHCH33OO

CHCH33OOCHCH33OO

CHCH33OCHOCH22

CHCH22OOCHCH33

HH OOHH

OOCHCH33HH

HHCHCH33OO

HH OOCHCH33

CHCH OO

Dr. Wolf's CHM 424 25- 144



CHCH22OOCHCH33

HH OOHH

OOCHCH33HH

HHCHCH33OO

HH OOCHCH33

CHCH OO

This carbon has This carbon has OOHHinstead of Oinstead of OCHCH33..

Therefore,its O was theTherefore,its O was theoxygenoxygen in the ring. in the ring.

Dr. Wolf's CHM 424 25- 145

End of Chapter 25End of Chapter 25

dr. wolf's chm 424 25- 1 modified chapter 25 carbohydrates

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