chapter 22 carbohydrates 22.1 introduction 21.1a classification of carbohydrates carbodydrares:...
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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 easilyHydrolysis 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:
CO2 + yH2O + solar energy¦Ö C¦Ö (H2O)y + O2¦Ö
Carbohydrate (̼ˮ»¯ºÏ Îï £©
CO2 + yH2O + energy¦ÖC¦Ö (H2O)y + O2¦Ö
Much of the energy is conserved in ATP. Plants and animals can usethe 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
Carbohydrates can be released energy when animals or plants
metabolize them to carbon dioxide and water.
22.2A CLASSIFICATION OF MONOSACCHARIDES
22.2 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
four carbon atoms
five carbon atoms
six carbon atoms
triose
tetrose
pentose
hexose
(±ûÌÇ)
(ËÄÌÇ)
(Îì ÌÇ)
(¼ºõ±)
These two classification are frequently combined. For example:
C4 aldose aldotetrose(¶¡ È©ÌÇ£©
C5 ketose ketopentose
(Îì ͪ ÌÇ£©
O
CH
CHOH
CHOH
CH2OH
O
CH
(CHOH)n
CH2OH
CH2OH
C
(CHOH)n
O
CH2OH
CH2OH
C O
CHOH
CHOH
CH2OH
An aldose (È©õ±)
A ketose (ͪ ÌÇ£©
aldotetrose(¶¡ È©ÌÇ£©
ketopentose(Îì ͪ ÌÇ£©
22.2B D AND L DESIGNATIONS OF MONOSACCHARIDES
Glyceraldehyde exists two enantiomeric forms which have the absolute configurations:
O
C
C
CH2OH
OHH
H
O
C
C
CH2OH
HHO
H
(+)-Glyceraldehyde (+)-¸ÊÓÍÈ©
(-)-Glyceraldehyde (-)-¸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.
CHO
CHOH
CHOH
C
CH2OH
C
CHOH
CHOH
C
CH2OH
OHH HHO
*
* *
*
O
CH2OH
Highest number sterocenter
1
2 3
4
5
1
2
3
4
D-aldopentose (D-Îì È©ÌÇ£©
L-ketohexose (L-¼ºÍª ÌÇ£©
D and L designations are not necessarily related to the optical rotations of the sugars to which they are applied.
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
HO H
H OH
H OH
CH2OH
CHO
CH OH
C
C
HO H
C
H OH
H OH
CH2OH
CHO
HHO
OHH
OHH
H OH
CH2OH
Fisher projection formula
Cirele-and-line formula
Wedge-line-dashed wedge formula
1 2 3
Open –chair structure (1, 2, or 3) exists equilibrium with two cyclic forms 4 and 5 or 6 and 7.
OH
OH
H
OHH
OHH
OH
CH2OH
HOH
OH
OH
HH
OHH
OH
CH2OH
H
4 5
6 7
Haworth formulas
+
+
OHOHO
H2COH
OHOH
OHOHO
H2COH
OHOH
¦Á-D-(+)-Glucopyranose(¦Á-D-(+)-ßÁà«(ÐÍ)ÆÏÌÑÌÇ)
¦Â-D-(+)-Glucopyranose(¦Â-D-(+)-ßÁà«(ÐÍ)ÆÏÌÑÌÇ)
The cyclic forms of D-(+)-Glucose are hemiacetals formed by an intramolecular reaction of the –OH group at C-5 with the aldehydegroup.
CC
H
OH
CC
OH
H
C
H
OH
H
OH
HOH2C O
H
123456 CHO
CH2OHH
OH
H
OHH
OH
H
OH
1
23
4
5
6
(plane projection formula)when a model of this is made. it will coil as follows If the group attached to
C-4 is pivoted as the arrows indicate
CH
OH
OH
H
OHH
OH
CH2OH
H
1
23
4
5
6 H
O C
OH
OH
H
OHH
OH
CH2OH
H
1
23
4
5
6
OH
H
*
C
OH
OH
H
OHH
OH
CH2OH
H
1
23
4
5
6
H
OH*
this -OH group adds accross the to close a ring makea cyclic hemiacetal
O
¦Á-D-(+)-Glucopyranose(¦Á-D-(+)-ßÁà«(ÐÍ)ÆÏÌÑÌÇ)
¦Â-D-(+)-Glucopyranose(¦Â-D-(+)-ßÁà«(ÐÍ)ÆÏÌÑÌÇ)
Open-chain form of D-glucose (¿ªÁ´ÐÍD-ÆÏÌÑÌÇ£©
(start -OH is the hemiacetal OH. which in ¦Á-glucose is on the oppsite side of the ring from the -CH2OH group at C-5 )
(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 )
Notes:
(2) In carbohydrate chemistry diastereomers of this type are called anomers, and the hemiacetal carbon atom is called the anomericCarbon 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
(1) These two cyclic forms are diastereomers that differ only in the configuration of 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 allowedto stand, its rotation changed.
Mutarotation: the change in rotation towards an equilibrium value.
OHO
H2C
OH
HO
OHOH
OHO
H2C
OH
HO
OH
OH
CHO
H OH
HO H
H OH
H OH
CH2OH
¦Á-D-(+)-Glucopyranose(¦Á-D-(+)-ßÁà«(ÐÍ)ÆÏÌÑÌÇ)(mp, 146¡æ [a]D
25 = +1120)
¦Â-D-(+)-Glucopyranose(¦Â-D-(+)-ßÁà«(ÐÍ)ÆÏÌÑÌÇ)(mp, 150¡æ [a]D
25 = +18.70)
Open-chain form of D-glucose(¿ªÁ´ÐÍD-ÆÏÌÑÌÇ£©
Ordinary D-(+)-glucose has the α configuration at the anomericcarbon atom and that higher melting form has the βconfiguration.
The percentage of the α andβanomers present at equilibrium.
OHO
H2C
OH
HO
OHOH
OHO
H2C
OH
HO
OH
OH
¦Á-D-(+)-Glucopyranose(¦Á-D-(+)-ßÁà«(ÐÍ)ÆÏÌÑÌÇ)(36% at equilibrium )
¦Â-D-(+)-Glucopyranose(¦Â-D-(+)-ßÁà«(ÐÍ)ÆÏÌÑÌÇ)(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:
CHOH
OHO
H2COH
HO
OH
D-(+)-Glucose
OHO
H2COH
HO
OH
OCH3
CHO
H OH
HO H
H OH
H OH
CH2OH
methyl ¦Â-D-Glucopyranose(¼×»ù ¦Â-D-(+)-ßÁà«(ÐÍ)ÆÏÌÑÌÇ)(mp, 107¡æ [a]D
25 = -330)
CH3OH
HCl
OHO
H2COH
HO
OHOCH3
methyl ¦Á-D-Glucopyranose(¼×»ù ¦Á-D-(+)-ßÁà«(ÐÍ)ÆÏÌÑÌÇ)(mp, 165¡æ [a]D
25 = +1580)
+
The mechanism for the formation of the methyl glucosides:
OHO
H2COH
HO
OH
OH
OHO
H2COH
HO
OHOHCH3
++ H+
- H+
OHO
H2COH
HO
OH
OH2
- H2O
+H2O
OHO
H2COH
HO
OH
+
+ HOCH3
OHO
H2COH
HO
OH
OHCH3
+
++ H+
- H+
+ H+
- H+
methyl ¦Á-D-Gluco- pyranoside
methyl ¦Â-D-Gluco- pyranoside
acetal of glucose
acetals of mannose
ketals of fructose
glucoside
mannosides
fructosides
Carbohydrate acetals, generally, are called glycosides. Foe example:
In acidic solutions, however, glycosides undergo hydrolysis to produce a sugar and alcohol:
OHO
H2COH
HO
OHOCH3
OHO
H2COH
HO
OHOH
H2O, H3O+ + R-OH
Glycoside (Åäõ±)
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.
C
CH OH
C
C
HO H
C
H OH
H OH
CH2OH
O
H C
C OH
C
C
HO H
C
H OH
H OH
CH2OH
O
H C
C OH
C
C
HO H
C
H OH
H OH
CH2OH
O
H C
CHO H
C
C
HO H
C
H OH
H OH
CH2OH
O
H
H2O
H2O OH-OH-
C
C OH
C
C
HO H
C
H OH
H OH
CH2OH
OH
H
H2OOH-
tautomerization
CH2OH
C O
C
C
HO H
C
H OH
H OH
CH2OH
22.5A FORMATION OF ETHERS
A methyl glucoside can be converted to the derivative by treatingit with excess dimethyl sulfate in aqueous sodium hydroxide.
OHO
HOH2C
HO
OHOCH3
OHO
HOH2C
HO
O-OCH3
OHO
HOH2C
HO
OCH3
OCH3
OH3CO
H2COCH3
H3CO
OCH3
OCH3
-OH CH3__OSO3CH3
repeatedmethylations
Methyl glucoside (¼×»ù.ÅäÌÇÎï )
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:
OH3CO
H2COCH3
H3CO
OCH3
OCH3
H3O+
H2O
OH3CO
H2COCH3
H3CO
OCH3
OH
CHO
H OCH3
H3CO H
H OCH3
H OH
CH2OCH3
2,3,4,6-tetra-O-methyl-D-glucose (2,3,4,6-Ëļ×Ñõ»ùÆÏÌÑÌÇ£©
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 monosaccharideconverts all of the hydroxyl groups to ester groups
OHO
HOH2C
HO
OHOH
(CH3CO)2O
Pyridine
OH3CO2C
H3CCOOH2C
H3CO2C
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 producecyclic acetals and ketals.
CH2OH
CH2OH+ O
H+
O
O
CH3
CH3
1,2-Diol(1,2-¶þ´¼£©
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.
O
OH
HOH2C
OHOH
HO CH3COCH3H2SO4
OHOH2C
OO
O
H3C
H3C
H3CCH3
0
+ 2H2O
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 specificeffect.
22.6A BENEDICT’S OR TOLLENS’REAGENTS: REDUCING SUGARS
Benedict’s and Tollens’ reagent give positive tests with aldoses and ketoses.
Cu+ +(complex) or Cu2O + oxidation products
O
CH
(CHOH)n
CH2OH
CH2OH
C
(CHOH)n
O
CH2OH
aldose
ketose
(brick-redreductionproduct)
Benedit'ssolution (blue)
Sugars that give positive tests with Tollens’or Benedict’s solutionsare known as reducing sugars, and all carbohydrates that containa 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
aldose(È©ÌÇ£©
Br2H2O
COOH
(CHOH)n
CH2OH
Aldonic acid£¨ 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 thealdonic acid may undergo a subsequent ring closure to form aγ –aldonolactone.
OHO
HOH2C
HO
OH
OH
OHO
HOH2C
HO
OH
OBr2H2O
+H2O
-H2O
COOH
H OH
HO H
H OH
H OH
CH2OH
H
H OH
OH HO
HHO
CH2OH
O+H2O
-H2O
¦Â-D-Glucopyranose (¦Â-D-ßÁà«(ÐÍ)ÆÏÌÑÌÇ)
D-Glucono-¦Ä-lactone (D-ÆÏÌÑÌÇ-¦Ä-ÄÚõ¥£©
D-Gluconic acid(D-ÆÏÌÑÌÇËᣩ
D-Glucono-¦Ãlactone (D-ÆÏÌÑÌÇ-¦Ã-ÄÚõ¥£©
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
aldose(È©ÌÇ£©
HNO3
COOH
(CHOH)n
CH2OH
Aldonic acid£¨ ÌÇËᣩ
It is not known whether a lactone is an intermediate in the oxidation of an aldose to an aldaric acid; however, aldaricacids from γandδ-lactones readily
C
CHOH
CHOH
CHOH
CHOH
C
O
OH
O
OH
-H2O
C
CHOH
HC
CHOH
CHOH
C
O
OH
O
C
CHOH
CHOH
HC
CHOH
C
O
O
OH
O or Corners such as this do not represent a -CH2 group
Aldaric acid (ÌÇËᣩ
¦Ã-lactone of an Aldaric acid (ÌÇËá--¦Ã-ÄÚõ¥£©
The aldaric acid obtained from D-glucose is called D-glucaric acid
OHO
HOH2C
HO
OH
HO
CHO
H OH
HO H
H OH
H OH
CH2OH
COOH
H OH
HO H
H OH
H OH
COOH
HNO3
D-GlucoseD-Glucaric acid (ÆÏÌÑÌǶþËᣩ
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 compoundsproduced.
C OH
C OH+ HIO4 O + HIO3 + H2O2
This reaction usually takes place in quantitative yield. By measuringthe 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.
+ 2 HIO4
H
O
H C
H
OH
C OHH
C OHH
HH
H
O
H C OH
O
+
+
formaldehyde (¼×È©)
formic acid (¼×Ëᣩ
formaldehyde (¼×È©)
H
+ 2 HIO4
C
O
OH
C OHH
C OHH
HH
H
O
H C OH
O
+
+
formic acid (¼×Ëᣩ
H C OH
O
formic acid (¼×Ëᣩ
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).
+ 2 HIO4
H
H
O
H C
H
OH
C O
C OHH
HH
H
O
O C O
+
+
formaldehyde (¼×È©)
carbon dioxide (¶þÑõ»¯Ì¼£©
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
CHO
(CHOH)n
CH2OH
aldose(È©ÌÇ£©
CH2OH
(CHOH)n
CH2OH
Alditol £¨ ÌÇ ¼£©
NaBH4orH2, Pt
Aldoses( and ketoses) can be reduced with sodium borohydride to compounds called alditols.
NaBH4
OHO
HOH2C
HO
OH
HO
CHO
H OH
HO H
H OH
H OH
CH2OH
CH2OH
H OH
HO H
H OH
H OH
CH2OH
D-GlucoseD-Glucitol (D-ÆÏÌÑÌÇ´¼£©
22.8 REACTIONS OF MONOSACCHARIDES WITH PHENYLHYDRAZINE: OSAZONES
The aldehyde group of an aldose react with such carbonyl reagentsas hydroxylamine and phenylhydrazine.
O
CH
(CHOH)n
CH2OH
H
C NNHC6H5
C
(CHOH)n
CH2OH
+ 3C6H5NHNH2 NNHC6H5+ C6H5NH2 + NH3 + H2O
phenylosazone (±½ëÛ)
Osazone formation results in a loss of the stereocenter at C-2 butdose not affect other stereocenters.
CHO
H OH
HO H
H OH
H OH
CH2OH
CH=NNHC6H5
C NNHC6H5
HO H
H OH
H OH
CH2OH
D-Glucose(ÆÏÌÑÌÇ£©
CHO
HO H
HO H
H OH
H OH
CH2OH
C6H5NHNH2 C6H5NHNH2
Same phenylosazone (±½ëÛ)
D-Mannose(¸Ê¶ÌÇ)
22.9 SYNTHESIS AND DEGRADATION OF MONOSACCHARIDES
22.9A KILIANI-FISCHER SYNTHESIS
Kiliani-fischer synthesis: the method of lengthening the carbon chain of the an aldose.
OH
CHO
CH2OH
H
OHH
CH2OH
OHH
CN
OHH
CH2OH
HHO
CN
HCl
(1) Ba(OH)2(2) H3O+
Epimericcyanohydrine(separated)
(1) Ba(OH)2(2) H3O+
O
CHO
H OH
H OH
CH2OH
Epimericaldonic acids
O
CHO
HO H
H OH
CH2OH
Epimeric¦Ã-aldonlactones
Na-Hg, H2OPh 3-5
Na-Hg, H2OPh 3-5
O
CH
H OH
H OH
CH2OH
O
CH
H OH
H OH
CH2OH
H
H
OH OH
H HO
OH
H
OH H
H HOO
O
We can be sure that the aldotetroses that we obtain from kiliani-fischersynthesis 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.
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 Dfamily with D-(-)-glucose being by far the most common.
22.11 FISCHER’S PROOF OF THE CONFIGURATION OF
D-(+)-GLUCOSE
CHO
H OH
H OH
H OH
CH2OH
COOH
H OH
H OH
H OH
CH2OH
Br2H2O
CHO
H OH
H OH
CH2OH
H2O2Fe2(SO4)3
D-(-)-Ribose(D-(-)-ºËÌÇ£©
D-Ribonic acid (D-ºËÌÇËᣩ
D-(-)-Erythrose
CHO
H OH
HO H
H OH
CH2OH
CHO
H OH
HO H
HO H
H OH
CH2OH
CHO
H OH
H OH
HO H
H OH
CH2OH
CHO
HO OH
H OH
HO H
H OH
CH2OH
CHO
HO H
HO H
HO H
H OH
CH2OH
CHO
HO H
HO H
H OH
CH2OH
CHO
HO H
H OH
CH2OHCHO
H OH
CH2OH
CHO
H OH
H OH
CH2OHAldotriose (±ûÈ©ÌÇ)
Aldotetroses (¶¡È©ÌÇ£©
Aldopentoses (Îì È©ÌÇ£©
Aldohexoses( ¼ºÈ©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.
CHO
H OH
HO H
H OH
H OH
CH2OH
end-groupinterchange
CH2OH
H OH
HO H
H OH
H OH
CH2OH
CHO
HO H
HO H
H OH
HO H
CH2OH
C
H OH
HO H
H
H OH
COOH
CH2OH
H OH
HO H
H OH
H OH
COOH
O
ONa-Hg
C
OHH
OHH
H
OHH
CH2OH
O
O
Na-Hg
pH 3-5
C
HO H
HO H
H
HO H
CH2OH
O
H
OH
CH
OHH
OHH
H
OHH
CH2OH
O
HO
¦Ã-lactone (¦Ã-ÄÚõ¥£©
L-Gulonic acid ¦Ã-aldonolactone (¦Ã-È©ÌÇÄÚõ¥£©
L-(+)-Gulose(L-(+)-ÆÏÌÑÌÇ£©
22.12A SUCROSE
22.12 DISACCHARIDES
Sucrose: the most widely occurring disaccharide of ordinary table sugar.
Structure:
C
OH
OH
H
OHH
OH
CH2OH
H
1
23
4
5
6
H
OOH H
H OH
OHOH2C
CH2OH
1
2
3 4
56
FromD-fructose
FromD-glucose
-Glucosidic linkage¦Á-Glucosidic linkage
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:
OHO
HO
HOH2C
OH
O
O
HO
HOH2C
OHOHNotes:
or
¦Á-Glucosidic linkage
C
OH
OH
H
OHH
OH
CH2OH
H
1
23
4
5
6
H
OC
OH
H
OHH
OH
CH2OH
H1
23
4
5
6
HO
H
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, , and β-(+)-maltose, [a]D
25 = +1120 [a]D25 = +1680
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-D- gluconic 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-methyl- D-glucose.
C
OH
OHH
OHH
OH
CH2OH
H1
23
4
5
6
H
OCHOH
OHH
OHH
OH
CH2OH
H
23
4
5
6
C
OH
OH
H
OHH
OH
CH2OH
HH
OCOOH
OHHH
OHH
OH
CH2OH
H C
OH
OCH3
H
OCH3H
OCH3
CH2OCH3
HH
O
OHH
OCH3H
OCH3
CH2OCH3
H OCH3
C
OH
OCH3
H
OCH3H
OCH3
CH2OCH3
HH
OCO2CH3
OCH3HH
OCH3H
OCH3
CH2OCH3
H
OH
OCH3
H
OCH3H
OCH3
CH2OCH3
HO
H
OCH3H
OCH3
COOCH3
H OHOH
H
OH+
Br2 / H2O (1) CH3OH, H+
(2) (CH3)2SO4, OH-
(CH3)2SO4 OH-
H+, H2O
2,3,4,6-tetra-O-methyl-D-glucose ( as pyranose)
2,3,6-tri-O-methyl-D-glucose ( as pyranose)
H+, H2O
1
OH
OCH3
H
OCH3H
OCH3
CH2OCH3
HCO2H
OCH3
H
OCH3H
OCH3
COOCH3
HOH
H
OH
+
2,3,4,6-tetra-O-methyl-D-glucose ( as pyranose)
2,3,5,6-tetra-O-methyl-D-gluconic acid
H+, H2O
22.12C CELLOBIOSE
Structure:
C
OH
OHH
OHH
OH
CH2OH
H1
23
4
5
6
O
H
OHH
OHH
OH
CH2OH
H
23
4
5
6
1
OH
H
¦Â-Glycosidic linkage
OHO
HO
HOH2C
OH
O
HO
HOH2C
OHOH
Oor
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-glucoseand D-galactose; the glycosidic linkage is β.
Structure:
C
OOH
HH
OHH
OH
CH2OH
H1
23
4
5
6
O
H
OHH
OHH
OH
CH2OH
H
23
4
5
6
1
OH
H
¦Â-Glucosidic linkage
FromD-galactose
FromD-glucose
or
O
HO
HOH2C
OH
O
HO
HOH2C
OHOH
O
HO
22.13 POLYSACCHARIDES
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:
In amylopectin the chains are branched. Branching takes placebetween C-6 and C-1at intervals of 20-25 glucose units.
C
OH
H
OHH
OH
CH2OH
HH
OCH
OH
H
OHH
OH
CH2OH
HOH
HO
n
n > 1000 1:4-glycosidic linkages
C
OH
OH
OHH
OH
CH2OH
HH
OC
OHH
OHH
OH
CH2OH
HOH
O
C
OH
OH
OHH
OH
CH2OH
HH
OC
OHH
OHH
OH
CH2OH
HH
C
OH
OH
OHH
OH
H2C
HH
OC
OHH
OHH
OH
CH2OH
HOH
O
¡
¡ ¡
Branch
Main chain
1:6 branch poinr
Partical structure of amylopectin:
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.
Glucose (from glycogen) is highly water soluble and as an idealSource of “ready energy”.
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.
22.13C CELLULOSE
A portion of cellulose structure:
C
OH
H
OHH
OH
CH2OH
HO
H
OHH
OHH
OH
CH2OH
H O
Hn
The glycosidic linkages are , 1: 4
The outside –OH groups are ideally situated to “zip” the chains make together by forming hydrogen bonds.
Special property:
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 basesolution.
Cellulose-OH + CS2NaOH
Cellulose-O-C-S-Na+=
S
cellulose xanthate(ÏËάËØ»ÇËáõ¥£©
The solution of cellulose xanthate is then passed through a smallOrifice or slit into an acidic solution.
Cellulose-O-C-S-Na+=
S
cellulose xanthate(ÏËάËØ»ÇËáõ¥£©
H3O+Cellulose-OH
22.14 OTHER BIOLOGICALLY IMPORTANT SUGARS
Uronic acids: monosaccharide derivatives in which the –CH2OHgroup at C-6 has been specifically oxidized to a carboxyl group.
For example:
Glucose Glucuronic acid
Galactose Galacturonic acid
CHO
H OH
HO H
H OH
H OH
CH2OH
CHO
H OH
HO H
HO H
H H
CH2OH
O
OH
OH
OH
COOH
OH
O
OH
OH
COOH
OH
OH
oror
D-Glucuronic acid (ÆÏ(ÌÑ)ÌÇÈ©Ëá)
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:
O
HO
HOH2C
OHNH2
HO
-D-Glucopyranosyl amine
H
CH2OH
OH OH
H HO
N
H
N
N
N
NH2
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.
OH
OH
OH
HH
NH2H
OH
CH2OH
HOH
OH
OH
HH
NHCOCH3H
OH
CH2OH
H
OH
OH
OH
HH
NHCOCH3H
OR
CH2OH
HH
CH3
COOH
R =
¦Â-D-Glucosamine(¦Â-D-ÆÏ(ÌÑ)ÌÇ°· )
¦Â-N-Acetyl-D-Glucosamine (NAM)
¦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.
Type A antigens carry anti-B antibodies in their serum; type B antigens carry anti-A antibodies in their serum; type AB cellshave both A and B antigens but have neither anti-A nor anti-Bantigens; type O cells have neither A nor B antigens but have both anti-A and anti-B antigens.
The A,B and H antigens differ only in the monodacchride units at
their nonreducing ends.
22.17 CARBOHYDRATE ANTIBIOTICS
Streptomycin: isolation of the carbohydrate antibiotic.
OHOH2C
HOHO
O
NHCH3
O O
HO
H
OHNHCNHNH2
OH
H
H
CHO
OHH3C HN C NH2
NH
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.
Streptomycin is made up of the following three subunits: