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CHAPTER 22
CARBOHYDRATES
22.1 INTRODUCTION
21.1A CLASSIFICATION OF CARBOHYDRATES
Carbodydrares: polyhydroxy aldehydes and ketones or substances
that hydrolyze to yield polyhydroxy aldehydes and
ketones.
Monosaccharides: simple carbohydrates cannot be hydrolyzed into
smaller simpler carbohydrates.
Disaccharides: on a molecular basis, carbohydrates that undergo
hydrolysis to produce only two molecules of
monosaccharide.
Trisaccharides: those carbohydrates that yield three molecules of
monosaccharide.
Polysaccharide: carbohydrates that yield a large number of molecules
of monosaccharide (﹥10).
Disaccharides Trisaccharides and Polysaccharide are easily
Hydrolysis to monosaccharide .
Carbohydrares are the most abundant organic constitutes of plants.
We encounter carbohydrates at almost every turn of our daily life.
21.1B PHOTOSYNTHESIS AND CARBOHYDRATE
METABOLESM
Carbohydrates are synthesized in green plants by photosynthesis:
¦Ö
CO2 + yH2O + solar energy
C¦ Ö(H2O)y + ¦ÖO2
Carbohydrate
(̼ˮ» ¯ºÏ Îï £©
Carbohydrates can be released energy when animals or plants
metabolize them to carbon dioxide and water.
C¦ Ö(H2O)y + ¦ÖO2
¦ÖCO2 + yH2O + energy
Much of the energy is conserved in ATP. Plants and animals can use
the energy of ATP to carry out all of their energy-requiring process.
When the energy in ATP is used, a coupled reaction takes place in
which ATP is hydrolyzed:
ATP + H2O -energy
ADP + Pi
22.2 MONOSACCHARIDES
22.2A CLASSIFICATION OF MONOSACCHARIDES
Monosaccharides are classified according to:
(1) The number of carbon atoms present in the molecular.
(2) whether they contain an aldehyde or keto group.
three carbon atoms
triose (±ûÌÇ)
four carbon atoms
tetrose (ËÄÌÇ)
five carbon atoms
six carbon atoms
pentose (Îì ÌÇ)
hexose (¼ºõ±)
These two classification are frequently combined. For example:
C4 aldose
aldotetrose
(¶¡ È©ÌÇ£©
ketopentose
C5 ketose
(Îì ͪ ÌÇ£©
O
CH2OH
O
CH2OH
CH
C
CH
C
CHOH
CHOH
O
O
(CHOH)n
(CHOH)n
CHOH
CHOH
CH2OH
CH2OH
CH2OH
CH2OH
An aldose
A ketose
aldotetrose
ketopentose
(ͪ ÌÇ£©
(¶¡ È©ÌÇ£©
(Îì ͪ ÌÇ£©
(È©õ±)
22.2B
D AND L
DESIGNATIONS OF MONOSACCHARIDES
Glyceraldehyde exists two enantiomeric forms which have the
absolute configurations:
O
O
H
C
H
C
OH
CH2OH
HO
C
H
C
H
CH2OH
(+)-Glyceraldehyde
(-)-Glyceraldehyde
(+)-¸ÊÓÍÈ©
(-)-¸ÊÓÍÈ©
(+)-Glyceraldehyde should be designated (R)-(+)- Glyceraldehyde
and (-)-Glyceraldehyde should be designated (S)-(-)- Glyceraldehyde
(section 5.5)
Other system designated (+)-Glyceraldehyde as D-(+)- Glyceraldehyde
and (-)-Glyceraldehyde as L-(-)-Glyceraldehyde.
1 CH2OH
1 CHO
H
2 C
O
2 * CHOH
3 * CHOH
3 * CHOH
4 * CHOH
4
C
OH
5 CH2OH
D-aldopentose
(D-Îì È©ÌÇ£©
HO
Highest number sterocenter
C
H
CH2OH
L-ketohexose
(L-¼ºÍª ÌÇ£©
and L designations are not necessarily related to the optical
rotations of the sugars to which they are applied.
D
22.2C ATRUCTURAL FORMULAS FOR MONOSACCHARIDES
Fisher projection formula: horizontal lines project out towards the
reader and vertical lines project behind the plane of the page.
CHO
H
OH
CHO
H
OH
HO
H
H
OH
H
OH
CH2OH
Fisher projection
formula
1
CHO
HO
H
H
H
OH
OH
CH2OH
Cirele-and-line
formula
2
H
C
OH
HO
C
H
H
C
OH
H
C
OH
CH2OH
Wedge-line-dashed
wedge formula
3
CH2OH
H
O
H
OH
H
+
H
H
OH
OH
H
CH2OH
O
H
H
OH
H
OH
OH
H
Haworth formulas
4
OH
5
OH
HO
HO
H2 C
OH
OH
O
OH
OH
6
¦Á-D-(+)-Glucopyranose
(¦Á-D-(+)-ßÁà«(ÐÍ)Æ ÌÏÑÌÇ)
HO
HO
+
H2 C
OH
O
OH
7
¦Â-D-(+)-Glucopyranose
(¦Â-D-(+)-ßÁà«(ÐÍ)Æ ÌÏÑÌÇ)
Open –chair structure (1, 2, or 3) exists equilibrium with two
cyclic forms 4 and 5 or 6 and 7.
The cyclic forms of D-(+)-Glucose are hemiacetals formed by an
intramolecular reaction of the –OH group at C-5 with the aldehyde
group.
H
HOH2C
C
6 5
H
4
C
OH H
C
3
OH OH H
C
2
H
H
1
C
O
OH
(plane projection formula)
when a model of this is
made. it will coil as
follows
H
4
5
OH
OH
OH 3
H
6
CH2OH
H
CHO
1
2
OH
If the group attached to
C-4 is pivoted as the
arrows indicate
this -OH group adds
O
accross the
to close a ring make
a cyclic hemiacetal
6 CH2OH
5
O
H
OH
H
H
4
OH 3
H
2
H
C
1
* OH
OH
¦Á-D-(+)-Glucopyranose
(¦Á-D-(+)-ßÁà«(ÐÍ)Æ ÏÌÑÌÇ)
(start -OH is the hemiacetal
OH. which in ¦Á-glucose is
on the oppsite side of the
ring from the -CH2 OH
group at C-5 )
Notes:
H
6 CH2OH
5
O
H
OH
H
H
4
OH 3
H
6 CH2OH
5
O
H
OH
H
H
CH
1
O
2
OH
Open-chain form of D-glucose
(¿ªÁ´ÐÍD-ÆÏÌÑÌÇ£©
4
OH 3
H
2
* OH
C
1
H
OH
¦Â-D-(+)-Glucopyranose
(¦Â-D-(+)-ßÁà«(ÐÍ)Æ ÌÏÑÌÇ)
(start -OH is the hemiacetal
OH. which in ¦Â-glucose is
on the same side of the
ring as the -CH2OH group
at C-5 )
(1) These two cyclic forms are diastereomers that differ only
in the configuration of C-1.
(2) In carbohydrate chemistry diastereomers of this type are called
anomers, and the hemiacetal carbon atom is called the anomeric
Carbon atom
( 3) In the orientation shown the αanomer has the –OH down and
the βanomer has the –OH up.
(4) The actual conformations of the rings are the chair forms. In the
β anomer of D-glucose, all of the large substituents, -OH, or
–CH2OH , are equatorial. In the α anomer, the only bulky axial
substituent is the -OH at C-1
22.3 MUTAROTATION
The optical rotations of αand βforms are found to be significantly
different,but when an aqueous solution of either form is allowed
to stand, its rotation changed.
Mutarotation: the change in rotation towards an equilibrium value.
CHO
OH
H
H2C
O
HO
HO
OH
OH
¦Á-D-(+)-Glucopyranose
(¦Á-D-(+)-ßÁà«(ÐÍ)Æ ÌÏÑÌÇ)
(mp, 146¡æ [a]D25 = +1120)
HO
OH
OH
H
H
OH
H
OH
CH2OH
Open-chain form
of D-glucose
(¿ªÁ´ÐÍD-ÆÏÌÑÌÇ£©
H2C
O
HO
HO
OH
OH
¦Â-D-(+)-Glucopyranose
(¦Â-D-(+)-ßÁà«(ÐÍ)Æ ÌÏÑÌÇ)
(mp, 150¡æ [a]D25 = +18.70)
Ordinary D-(+)-glucose has the α configuration at the anomeric
carbon atom and that higher melting form has the βconfiguration.
The percentage of the α andβanomers present at equilibrium.
OH
OH
H 2C
H2C
O
HO
HO
O
HO
HO
OH
OH
¦Á-D-(+)-Glucopyranose
(¦Á-D-(+)-ßÁà«(ÐÍ)Æ ÏÌÑÌÇ)
(36% at equilibrium )
OH
OH
¦Â-D-(+)-Glucopyranose
(¦Â-D-(+)-ßÁà«(ÐÍ)Æ ÏÌÑÌÇ)
(64% at equilibrium)
22.4 GLYCOSIDE FORMATION
When a small amount of gaseous hydrogen chloride is passed into
a solution of D-(+)-glucose in methanol, the reaction as follows:
CHO
H
HO
OH
H2C
OH
H
H
OH
H
OH
O
HO
HO
CHOH
OH
HCl
D-(+)-Glucose
CH2OH
OH
OH
H2C
HO
HO
CH3OH
H2C
O
+
OH
OCH3
methyl ¦Á-D-Glucopyranose
(¼×»ù ¦Á-D-(+)-ßÁà«(ÐÍ)Æ ÌÏÑÌÇ)
(mp, 165¡æ [a]D25 = +1580)
HO
HO
O
OCH3
OH
methyl ¦Â-D-Glucopyranose
(¼×»ù ¦Â-D-(+)-ßÁà«(ÐÍ)Æ ÌÏÑÌÇ)
(mp, 107¡æ [a]D25 = -330)
The mechanism for the formation of the methyl glucosides:
OH
OH
H2C
H2C
O
HO
HO
+H
OH
-
+
H+
O
HO
HO
OH
- H2 O
+
OH2
+H2O
OH
OH
H2C
OH
H2C
HO
HO
O
HO
HO
+
OHCH3
+
OH
O
+ HOCH3
+ H+
- H+
methyl
¦Â-D-Glucopyranoside
OH
OH
H2C
HO
HO
O
+ H+
- H+
OH +
OHCH3
methyl
¦Á-D-Glucopyranoside
Carbohydrate acetals, generally, are called glycosides. Foe example:
acetal of glucose
glucoside
acetals of mannose
mannosides
fructosides
ketals of fructose
In acidic solutions, however, glycosides undergo hydrolysis to
produce a sugar and alcohol:
OH
OH
H2C
HO
HO
H2C
O
OCH3
OH
Glycoside
(Åäõ±)
H2O, H3
O+
HO
HO
O
OH
+ R-OH
OH
Sugar
(õ±)
Aglycone
(ÌÇÜÕÅä»ù)
22.5 REACTIONS OF MONOSACCHARIDES
Dissolving monosaccharides in aqueous base causes them to undergo
a series of keto-enol tauomerizations that lead to isomerizastions.
O
O
H
C
H
C
OH
HO
C
H
OH-
H
C
OH
H2O
H
C
OH
H
CH2OH
C
H
C
OH
HO
C
H
H
C
H
C
OH
HO
C
H
OH
H
C
OH
OH
H
C
OH
CH2OH
CH2OH
H2O
OH
CH2OH
O
HO
C
H
H
C
OH
H
C
C
C
OH-
C
O
O
tautomerization
H
C
C
OH
HO
C
H
OH
H
C
OH
CH2OH
H
C
OH
CH2OH
H2O
OH-
H
C
HO
C
H
HO
C
H
H
C
OH
H
C
OH
CH2OH
22.5A FORMATION OF ETHERS
A methyl glucoside can be converted to the derivative by treating
it with excess dimethyl sulfate in aqueous sodium hydroxide.
HOH2C
HOH2C
O
HO
HO
-OH
OCH3
O
HO
HO
CH3__OSO3CH3
OCH3
O-
OH
Methyl glucoside
(¼×» ù.ÅäÌÇÎï )
OCH3
H2C
HOH2C
HO
HO
O
OCH3
OCH3
repeated
methylations
H3CO
H3CO
O
OCH3
OCH3
Pentamethyl derivative
(Îå ¼×» ùÑÜÉúÎï £©
The methoxy groups at C-2,C-3,C-4 and C-6 atoms are stable in dilute
aqueous acid, but C-1is different from the others because it is Part of
an acetal linkage.
Under dilute aqueous acid the methoxy group at C-1 will hydrolyze:
CHO
OCH3
OCH3
H3CO
H3CO
H
H2C
H2C
H3O+
O
OCH3
OCH3
H2O
H3CO
H3CO
O
H3CO
OH
OCH3
OCH3
H
H
OCH3
OH
H
CH2OCH3
2,3,4,6-tetra-O-methyl-D-glucose
(2,3,4,6-Ëļ×Ñõ» ùÆ ÏÌÑÌÇ£©
The oxygen at C-5 dose not bear a methyl group brcause it was
originally a part of the cyclic hemiacetal linkage of D-glucose
25.5B CONVERSION TO ESTERS
Under excess acetic anhydride and a weak base monosaccharide
converts all of the hydroxyl groups to ester groups
H3CCOOH2C
HOH2C
HO
HO
O
(CH3CO)2O
Pyridine
OH
OH
H3CO2C
H3CO2C
O
CO2CH3
O2CCH3
If the reaction is carried out at a low temperature, the reaction
occurs stereospecifically:the αanomer gives the α-acetate and
the βanomer gives the β-acetate.
22.5C CONVERSION TO CYCLIC ACETALS AND KETALS
Aldehydes and ketones react with open-chain 1,2-diols to produce
cyclic acetals and ketals.
CH2OH
+
CH2OH
1,2-Diol
(1,2-¶þ´¼£©
H+
O
CH3
O
CH3
O
Cyclic ketal
(»·Ëõͪ )
If the 1,2-diol is attached to a ring, as in a monosaccharide,
formation of the cyclic acetal or ketal occurs only when the
vicinal hydroxyl froups are cis to each other.
0
OH
HOH2C
HO
H3C
O
CH3COCH3
H2SO4
OH
OH
HOH2C
O
H3C
O
+ 2H2O
O
H3C
O
CH3
This reaction can be used to protect certain hydroxyl groups of a
sugar while reactions are carried out on other parts of the molecule.
22.6 OXIDATION REACTIONS OF MONOSACCHARIDES
The most important oxidizing agents are:
(1) Benedict’s or Tollens’ reagent
(2) bromine water
(3) nitric acid
(4) periodic acid.
Each of these reagents produces a different and usually specific
effect.
22.6A BENEDICT’S OR TOLLENS’REAGENTS:
REDUCING SUGARS
Benedict’s and Tollens’ reagent give positive tests with aldoses
and ketoses.
O
CH
(CHOH)n
CH2OH
aldose
Cu+ (complex) + or
Benedit's
solution
(blue)
CH2OH
C
O
(CHOH)n
CH2OH
ketose
Cu2O
+ oxidation products
(brick-red
reduction
product)
Sugars that give positive tests with Tollens’or Benedict’s solutions
are known as reducing sugars, and all carbohydrates that contain
a hemiacetal group or a hemoketal group give positive tests.
Carbohydrates that contain only acetal or ketal group do not give
positive tests with Tollens’or Benedict’s solution.
But neither of these reagents is useful as a preparative reagent in
carbohydrate oxidations.
Oxidations with both reagents take place in alkaline solution,
and in alkaline solutions sugars undergo a complex series of
reactions that lead to isomerization.
22.6B BROMINE WATER: THE SYNTHESIS
OF ALDONIC ACIDS
Bromine water is a general reagent that selectively oxidizes
-CHO group to a –COOH group.
CHO
(CHOH)n
CH2OH
COOH
Br2
H2O
(CHOH)n
CH2OH
aldose
Aldonic acid
(È©ÌÇ£©
£¨ÌÇËᣩ
Bromine water specifically oxidizes the βanomer, and the initial
product that forms is a δ–aldonolactone.
This compound may then hydrolyze to an aldonic acid, and the
aldonic acid may undergo a subsequent ring closure to form a
γ –aldonolactone.
HOH2C
HOH2C
O
HO
HO
OH
Br2
H2O
O
HO
HO
O
OH
-H2O
OH
¦Â-D-Glucopyranose
D-Glucono-¦Ä
-lactone
(D-Æ ÌÏÑÌÇ-¦ Ä
-ÄÚõ¥£©
(¦ Â
-D-ßÁà«(ÐÍ)Æ ÌÏÑÌÇ)
COOH
H
HO
CH2OH
OH
H
H
OH
H
OH
-H2O
H
+H2O
CH2OH
D-Gluconic acid
(D-Æ ÌÏÑÌÇËᣩ
HO
O
OH
H
H
OH
H
D-Glucono-¦Ã
lactone
(D-Æ ÌÏÑÌÇ-¦Ã
-ÄÚõ¥£©
+H2O
O
22.6C NITRIC ACID OXIDATION：ALDARIC ACIDS
Dilute nitric acid oxidizes both the –CHO group and the terminal
-CH2OH group of an aldose to –COOH groups.
CHO
(CHOH)n
CH2OH
COOH
HNO3
(CHOH)n
CH2OH
aldose
Aldonic acid
(È©ÌÇ£©
£¨ÌÇËᣩ
It is not known whether a lactone is an intermediate in the
oxidation of an aldose to an aldaric acid; however, aldaric
acids from γandδ-lactones readily
O
O
O
C OH
CHOH
C
CHOH
C OH
CHOH
CHOH
CHOH
-H2O
CHOH O
or
HC
HC
CHOH
CHOH
CHOH
CHOH
C
C
C
OH
O
Aldaric acid
(ÌÇËᣩ
OH
O
Corners such as
this do not
represent a
-CH2 group
O
¦Ã
-lactone of an Aldaric acid
(ÌÇËá--¦ Ã
-ÄÚõ¥£©
The aldaric acid obtained from D-glucose is called D-glucaric acid
CHO
HOH2C
HO
HO
H
O
HO
HO
OH
OH
H
H
HNO3
HO
OH
H
H
OH
H
OH
H
OH
H
OH
CH2OH
D-Glucose
COOH
COOH
D-Glucaric acid
(Æ ÌÏÑÌǶþËᣩ
22.6D PERIODATE OXIDATIONS: OXIDATIVE CLEAVAGE
OF POLYHYDROXY COMPOUNDS
Compounds that have hydroxyl groups on adjacent atoms undergo
oxidative cleavage when they are treated with aqueous periodic
acid. Carbon-carbon bonds breaks and carbonyl compounds
produced.
C
OH
C
OH
+ HIO4
2
O + HIO3 + H2 O
This reaction usually takes place in quantitative yield. By measuring
the number of molar equivalents valuable that are consumed in the
reaction, information can often be gained.
1. Three –CHOH groups : gives one molar equivalent of formiv acid
and two equivalents of formaldehyde.
H
H
C
formaldehyde
O
H
(¼×È©)
H +
OH
O
H
C
OH
H
C
OH
+ 2 HIO4
H
H
H
C
OH
(¼×Ëᣩ
+
O
H
formic acid
formaldehyde
(¼×È©)
2. Oxidative cleavage also takes place when an –OH group is
adjacent to the carbonyl group of an aldehyde or ketone(but
no that of an acid or an ester).
O
O
C
H
C
OH
(¼×Ëᣩ
+
OH
formic acid
O
H
C
OH
H
C
OH
+ 2 HIO4
H
H
H
C
OH
(¼×Ëᣩ
+
O
H
formic acid
formaldehyde
(¼×È©)
H
H
H
H
formaldehyde
O
H
C
OH
C
O
C
OH
+ 2 HIO4
O
H
H
(¼×È©)
+
C
O
(¶þÑõ»¯Ì¼£©
+
O
H
carbon dioxide
formaldehyde
(¼×È©)
3. Periodic acid dose not cleave compounds in which the hydroxyl
groups are separated by an intervening –CH2 group, nor those
in which a hydroxyl group is adiacent to an ether or acetal function.
22.7 REDUCTION OF MONOSACCHARIDES:ALDITOLS
Aldoses( and ketoses) can be reduced with sodium borohydride to
compounds called alditols.
CHO
(CHOH)n
CH2OH
CH2OH
NaBH4
or
H2, Pt
(CHOH)n
CH2OH
aldose
Alditol
(È©ÌÇ£©
£¨ ÌÇ´¼£©
CHO
HOH2C
HO
HO
H
O
HO
HO
OH
OH
H
H
NaBH4
HO
OH
H
H
OH
H
OH
H
OH
H
OH
CH2OH
D-Glucose
CH2OH
CH2OH
D-Glucitol
(D-Æ ÌÏÑÌÇ´¼£©
22.8 REACTIONS OF MONOSACCHARIDES WITH
PHENYLHYDRAZINE: OSAZONES
The aldehyde group of an aldose react with such carbonyl reagents
as hydroxylamine and phenylhydrazine.
O
H
CH
C
(CHOH)n
CH2OH
+ 3C6H5NHNH2
NNHC6H5
C NNHC6H5
+ C6H5NH2 + NH3 + H2O
(CHOH)n
CH2OH
phenylosazone
(±½ëÛ)
Osazone formation results in a loss of the stereocenter at C-2 but
dose not affect other stereocenters.
CHO
H
HO
CH=NNHC6H5
C
OH
H
H
OH
H
OH
CH2OH
D-Glucose
(Æ ÏÌÑÌÇ£©
HO
C6H5NHNH2
CHO
NNHC6H5
HO
H
H
HO
H
H
OH
H
OH
C6H5NHNH2
CH2OH
Same phenylosazone
(±½ëÛ)
22.9 SYNTHESIS AND DEGRADATION OF
MONOSACCHARIDES
22.9A KILIANI-FISCHER SYNTHESIS
H
OH
H
OH
CH2OH
D-Mannose
(¸Ê¶ÌÇ)
Kiliani-fischer synthesis: the method of lengthening the carbon chain
of the an aldose.
CHO
H
OH
CH2OH
HCl
CN
CN
H
OH
H
OH
CH2OH
(1) Ba(OH)2
(2) H3O+
HO
H
Epimeric
H
OH
cyanohydrine
CH2 OH
(separated)
(1) Ba(OH)2
(2) H3O+
O
O
HO
HO
C
H
OH
H
OH
HO
Epimeric
aldonic acids
H
H
H
O
H
O
H
OH
OH
H
OH
O
HO
H
Epimeric
¦Ã-aldonlactones OH
H
O
O
H
C
C
H
OH
H
OH
H
OH
H
OH
CH2OH
O
Na-Hg, H2O
Ph 3-5
Na-Hg, H2O
Ph 3-5
H
H
CH2OH
CH2OH
H
C
CH2OH
We can be sure that the aldotetroses that we obtain from kiliani-fischer
synthesis are both D sugar because the starting compound is
D-glyceraldehyde and its stereocenter is unaffected.
22.9B THE RUFF DEGRADATION
The Ruff degradation can be used to shorten the chain by a similar
unit.
The Ruff degradation involves:
(1) Oxidation of the aldose to an aldonic acid.
(2) Oxidative decarboxylation of the aldonic acid to the next lower
aldose.
CHO
H
OH
H
OH
H
OH
CH2OH
D-(-)-Ribose
(D-(-)-ºËÌÇ£©
COOH
Br2
H2O
H
OH
H
OH
H
OH
CHO
H2O2
Fe2(SO4)3
H
OH
H
OH
CH2OH
CH2OH
D-Ribonic acid
(D-ºËÌÇËᣩ
D-(-)-Erythrose
22.10 THE D FAMILY OF ALDOSES
We can place all of the aldose into families or “family trees” based
on their relation to D- or L-glyceraldehyde
Most, but not all, of the naturally occurring aldose belong to the D
family with D-(-)-glucose being by far the most common.
22.11 FISCHER’S PROOF OF THE CONFIGURATION OF
D-(+)-GLUCOSE
CHO
CHO
CHO
H
OH
HO
OH
H
H
OH
H
OH
H
HO
HO
H
H
H
OH
HO
H
HO
H
HO
H
Aldohexoses
HO
H
HO
H
( ¼ºÈ©ÌÇ£©
OH
CHO
H
HO
H
H
OH
CH2OH
OH
HO
H
H
HO
H
OH
H
Aldopentoses
(Îì È©ÌÇ£©
OH
CH2OH
CHO
OH
OH
CHO
CH2OH
H
H
CH2OH
CH2OH
CH2OH
OH
H
OH
CHO
CHO
HO
H
CHO
CH2OH
H
OH
CH2OH
H
OH
CH2OH
Aldotetroses
(¶¡È©ÌÇ£©
Aldotriose
(±ûÈ©ÌÇ)
Fischer’s assignment was based on the following reasoning.
(1) Nitric acid oxidation of (+)-glucose gives an optically active
aldaric acid.
(2) Degradation of (+)-glucose gives (-)-arabinose, and nitric acid
oxidation of (-)-arabinose gives an optically active aldaric acid.
(3) A Kiliani-Fischer synthesis beginning with (-)-arabinose gives
(+)-glucose and (+)-mannose; nitric acid oxidation of
(+)-mannose gives an optically active aldaric acid.
(4) Fischer had already developed a method for effectively
interchanging the two end groups(CHO and CH2OH) of an
aldose chain.
H
HO
H
OH
H
H
end-group
OH interchange
H
OH
HO
H
H
HO
H
H
OH
COOH
¦Ã
-lactone
(¦ Ã
-ÄÚõ¥£©
H
H
HO
H
OH
H
H
OH
HO
OH
H
CH2OH
CH2OH
CH2OH
C
HO
HO
H
O
OH
Na-Hg
O
H
OH
CH2OH
CH2OH
H
CHO
CH2OH
CHO
H
H
OH
OH
H
H
OH
OH
O
H
Na-Hg
OH pH 3-5
H
OH
O
C H
CH2OH
H
OH
HO
H
H
OH
H
OH
HO
H
HO
H
H
OH
HO
H
COOH
C
O
L-Gulonic acid
¦Ã
-aldonolactone
L-(+)-Gulose
(¦ Ã
-È©ÌÇÄÚõ¥£©
(L-(+)-Æ ÌÏÑÌÇ£©
CH
O
CH2OH
22.12 DISACCHARIDES
22.12A SUCROSE
Sucrose: the most widely occurring disaccharide of ordinary table
sugar.
Structure:
6 CH2OH
From
D-glucose
H
4
5
H
OH
OH 3
H
1
O
H
HOH2C
H
2
C
1
2
O
O
H
3
OH
OH
4
5
6
CH2OH
H
OH
¦Á-Glucosidic linkage
-Glucosidic linkage
From
D-fructose
The structure of sucrose is based on the following evidence:
1. Sucrose has the molecular formula C12H22O11
2. Acid-catalyzed hydrolysis of 1 mol of sucrose yields 1 mol
of D-glucose and 1 mol of D-frutose.
3. 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.
4. The hydrolysis of sucrose indicates an α configuration at the
glucoside portion and an enzyme known to hydrolyze a
β-fructofuranosides.
5 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.
22.12B
MATOSE
Structure:
6 CH2OH
5
O
H
OH
H
H
4
6 CH2OH
OH 3
H
H
H
C
1
4
O
2
5
O
H
OH
H
3
2
OH
H
HO
C1
H
OH
¦Á-Glucosidic linkage
or
HOH2C
O
HO
HO
Notes:
HOH2C
OH
O
HO
O
OH
OH
1. When 1 mol of maltose is subjected to acid-catalyzed hydrolysis,
it yield 2 mol of D-(+)-glucose.
2. Maltose is a reducing sugar.
3. Maltose exists in two anomeric forms: α-(+)-maltose,
25 = +1120
25
0 , and β-(+)-maltose,
[a]
D
[a]D = +168
4. Maltose reacts with bromine water to form a monocarboxylic
acid, maltose acid.
5. 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-Dgluconic acid.
6. Methylation of maltose itself, followed by hydrolysis, gives
2,3,4,6-tetra-O-methyl-D-glucose and 2,3,4,6-tri-O-methylD-glucose.
6 CH
H
5
2OH
H
OH
4
OH
3
H
6 CH
2OH
O
H
2
C
1
HH
O
OH
O
5
H
OH
4
H
1
CHOH
2
3
H
OH
(1) CH3OH, H+
(2) (CH3)2SO4, OH-
Br2 / H2O
H
CH2OH
O
H
H
OH
C
HH
O
OH
H
OH
CH2OH
OH
H
H COOH
OH
H
(CH3)2SO4
OH-
CH2OCH3
O
H
H
H
H
OCH3 H C
O
OCH3
H
OCH3
OH
CH2OCH3
OCH3
H
OCH3 H CO2CH3
H
H+, H2O
OCH3
CH2OCH3
CH2OCH3
O
H
H
O
H
H
H
OCH3 H C
OCH3 H
O
OCH3
H
OCH3
H
OCH3
H+, H2O
CH2OCH3
O
H
H
OCH3 H
OCH3
H
OCH3
2,3,4,6-tetra-Omethyl-D-glucose
( as pyranose)
OCH3
COOCH3
O
H
OCH3 H
H
OH +
OH
OH
H
OCH3
2,3,6-tri-Omethyl-D-glucose
( as pyranose)
H+, H2O
CH2OCH3
O
H
H
OCH3 H
OCH3
H
OCH3
COOCH3
OCH3
H
OCH3 H CO2H
H
OH
+
OH
H
2,3,4,6-tetra-Omethyl-D-glucose
( as pyranose)
OCH3
2,3,5,6-tetra-Omethyl-Dgluconic acid
22.12C CELLOBIOSE
Structure:
6 CH
2OH
¦Â-Glycosidic linkage
5
H
H
OH
6 CH
2OH
H
4
OH
5
H
OH
3
H
O
H
2
OH
O
C
1
4
OH
H
1
2
3
H
H
O
OH
H
HOH2C
or
HO
HO
O
HOH2C
O
O
OH
HO
OH
OH
Notes:
1. Cellobiose is a reducing sugar.
2. Cellobiose also undergoes mutarotation and forms a
phenylosazone.
3. Cellobiose is hydrolyzed by β-glucosidases. This is indicate
that the glycosidic linkage in cellobiose is β.
22.12D LACTOSE
Lactose is a reducing sugar that hydrolyzes to yield D-glucose
and D-galactose; the glycosidic linkage is β.
Structure:
6 CH
2OH
¦Â-Glucosidic linkage
5
H
H
OH
6 CH
2OH
From
D-galactose
OH
4
H
5
H
OH
3
H
O
O
4
H
1
2
OH
H
1
H
From
D-glucose
H
2
3
C
O
OH
H
OH
or
HO
HOH2C
HO
O
HOH2C
O
O
OH
HO
22.13 POLYSACCHARIDES
OH
OH
Homopolysaccharides: polysaccharides that are polymers of a single
monosaccharide.
Heteropolysaccharides: those made up of more than one type of
monosaccharide.
Glucan: a homopolysaccharide consisting of glucose monomeric
units.
Galactan: a homopolysaccharide consisting of galactose units
Three important polysaccharides, all of which are glucans,
glycogen, starch and cellulose.
22.13A STARCH
Heating starch with water produce amylose (10-20%)and
amylopectin(80-90%).
Structure of amylose:
CH2OH
CH2OH
O
H
H
OH
H
H
H
C
O
H
OH
H
OH
CH
O
H
OH
n > 1000
HO
H
OH
n
1:4-glycosidic linkages
In amylopectin the chains are branched. Branching takes place
between C-6 and C-1at intervals of 20-25 glucose units.
Partical structure of amylopectin:
Branch
CH2OH
O
H
H
OH
H
¡-
O
OH
Main chain CH2OH
¡-
O
O
H
OH
H
C
HH
O
H
HH
O
H
H
C
CH2OH
O
H
H
OH
OH
H
CH2OH
O
H
H
OH
H
OH
OH
C
OH
O
 1:6 branch poinr
H2C
H H
C O
O
H
OH
H
C
HH
O
H
OH
CH2OH
O
H
H
OH
OH
C
O
H
OH
The molecular weight is about 1-6 milion, include hundreds of
interconnecting chains of 20-25 glucose units.
¡-
22.13B GLYCOGEN
In glycogen the chain are much more highly branched and the
molecular weights as high as 100 million.
The size and structure of glycogen suits its function:
(1) Its size makes it too large to across cell membranes.
(2) The structure of glycogen solves the enormous of osmotic
pressure within the cell.
(3) The high branch structure of glycogen simplify the cell’s
logistical problems.
Glucose (from glycogen) is highly water soluble and as an ideal
Source of “ready energy”.
22.13C CELLULOSE
A portion of cellulose structure:
H
H
CH2OH
O
H
H
OH
CH2OH
O
H
H
OH
O
C
O
H
H
OH
n
H
H
OH
The glycosidic linkages are  , 1: 4
Special property:
The outside –OH groups are ideally situated to “zip” the chains
make together by forming hydrogen bonds.
Zipping many cellulose chains together in this way gives a highly
insoluble.
22.13D CELLULOSE DERIVATIVES
Most of the cellulose derivatives include two or three free hydroxyl
groups of each glucose unit which have been converted to an eater
or an ether.
Rayon is made by treating cellulose with carbon disulfide in base
solution.
NaOH
=
Cellulose-OH + CS2
S
Cellulose-O-C-S-Na+
cellulose xanthate
(ÏËάËØ» ÇËáõ¥£©
The solution of cellulose xanthate is then passed through a small
Orifice or slit into an acidic solution.
=
S
+
+ H3O
Cellulose-O-C-S Na
cellulose xanthate
Cellulose-OH
(ÏËάËØ» ÇËáõ¥£©
22.14 OTHER BIOLOGICALLY IMPORTANT SUGARS
Uronic acids: monosaccharide derivatives in which the –CH2OH
group at C-6 has been specifically oxidized to a carboxyl group.
For example:
Glucose
Glucuronic acid
Galactose
Galacturonic acid
CHO
CHO
H
HO
COOH
OH
COOH
OH
O
H
H
or
OH
H
OH
OH
OH
OH
H
O
OH or
OH
OH
OH
HO
H
HO
H
H
H
CH2OH
CH2OH
D-Glucuronic acid
(Æ Ï(ÌÑ)ÌÇÈ©Ëá)
OH
D-Galacturonic acid
(°ë ÈéÌÇÈ©Ëá)
Deoxy sugars: monosaccharides in which an –OH group has been
replaced by –H.
22.15 SUGARS THAT CONTAIN NITROGEN
22.15A GLYCOSYLAMINES
Glycosylamine: sugars in which an amino group replaces the
anomeric –OH. For example:
NH2
N
HOH2C
O
HO
HO
NH2
OH
 -D-Glucopyranosyl amine
CH2OHO
H
H
OH
N
N
N
H
H
OH
Adenosine
(ÏÙÜÕ)
Nucleoside: glycosylamines in which the amino component is a
pyrimidine or a purine and in which the sugar
component is either D-ribose or 2-deoxy-D-ribose.
22.15B AMINO SUGARS
Amino sugar: a sugar in which an amino group replaces a
nonanomeric –OH group.
CH2OH
O
H
H
OH
H
OH
H
OH
H
NH2
¦Â-D-Glucosamine
(¦ Â
-D-Æ Ï(ÌÑ)ÌÇ°· )
H
CH2OH
O
H
H
OH
OH
H
OH
H
NHCOCH3
¦Â-N-Acetyl-D-Glucosamine
(NAM)
H
CH2OH
O
H
H
OR
CH3
OH
R=
H
OH
H
H
COOH
NHCOCH3
¦Â-N-Acetylmuramic acid
(NAG)
D-glucosamine can be obtained by hydrolysis of chitin. The repeating
units in chitin is N-acetylglucosamine and the glycosidic linkages are
β, 1:4. The structure of chitin is smaller than that of cellulose.
D-glucosamine can also be isolated from heparin.
22.16 GLYCOLIIPIDS AND GLYCOPROTEINS OF THE
CELL SURFACE
Glycolipids: the carbohydrates joined through gltcosidic linkages
to lipids.
Glycoproteins: the carbohydrates joined through gltcosidic linkages
to proteins.
Glycolipids and glycoproteins on the cells are known to be the
agents by which cells interact with other cells and with invading
bacteria and viruses.
The A,B and O blood types are determined, respectively, by the
A, B and H determinants on the blood cell surface.
The A,B and H antigens differ only in the monodacchride units at
their nonreducing ends.
Type A antigens carry anti-B antibodies in their serum; type B
antigens carry anti-A antibodies in their serum; type AB cells
have both A and B antigens but have neither anti-A nor anti-B
antigens; type O cells have neither A nor B antigens but have
both anti-A and anti-B antigens.
22.17 CARBOHYDRATE ANTIBIOTICS
Streptomycin: isolation of the carbohydrate antibiotic.
Streptomycin is made up of the following three subunits:
H
HO
H3C
OH
HOH2C
O
O
CHO
H
O
OH
NHCNHNH2
OH
H
HN C NH2
NH
O
HO
HO
NHCH3
Other members of this family are antibiotics called kanamycins,
neomycins, and gentamicins. All are based on an amino cyclitol
linked to one or more amino augars. The glycosidic linkage is
nearly always α.