Carbohydrates Sugars or Saccharides

1
CarbohydratesSugars or Saccharides

• One of the most abundant compounds of living
  cells
• In living cells (plants) -gt carbohydrates are
  made by photosynthesis
• Monosaccharides C3-C9
• Oligosaccharides 2-10 units

2
Carbohydrates
Monosaccharides (biological sugars ose)
Most frequently found in nature - hexoses
(six-carbon sugars) -gt glucose and fructose
-
pentoses (five-carbon sugars) -gt ribose
2 Enantiomers
S, R Configuration
Fischer Projection
Highest Oxidation state
3
Carbohydrates
Monosaccharides (biological sugars ose)
Most frequently found in nature - hexoses
(six-carbon sugars) -gt glucose and fructose
-
pentoses (five-carbon sugars) -gt ribose
Pyranoside
Furanoside
Aldoses
Ketoses
4
Carbohydrates
Monosaccharides
D-Aldoses in the range of C3-C6
5
Carbohydrates
Monosaccharides
D-Ketoses in the range of C3-C6
6
Carbohydrates
Monosaccharides
Stereochemistry
D-Erythrose L-Erythrose -gt Enantiomers D-Erythr
ose D-Threose -gt Diastereoisomers D-Erythrose
L-Threose -gt Diastereoisomers
D-glucose L-glucose -gt Enantiomers
7
Carbohydrates
Monosaccharides
Enolization and Isomerization
Epimerization
Epimerization
Base-catalysed in water -gt Epimerization
isomerization
Isomerization
8
Carbohydrates
Monosaccharides
Cyclic hemiacetals hemiketals
9
Carbohydrates
Monosaccharides
Cyclic hemiacetals hemiketals -gt glucose
10
Carbohydrates
Monosaccharides
Cyclic hemiacetals hemiketals -gt glucose
a
b
D
L
a-Sugars have the -CH2OH group and the anomeric
hydroxyl group trans.
ß-Sugars have the -CH2OH group and the anomeric
hydroxyl group cis.
11
Carbohydrates
Monosaccharides
Cyclic hemiacetals hemiketals -gt glucose
Glucopyranoside more stable -gt almost 100 in
pyranoside form
12
Carbohydrates
Monosaccharides
Cyclic hemiacetals hemiketals -gt ribose
In solution mainly in pyranoside form (76) In
nucleotides (or other combinations) mostly found
in furanose form
13
Carbohydrates
Monosaccharides
Cyclic hemiacetals hemiketals -gt fructose
14
Carbohydrates
Monosaccharides
Cyclic hemiacetals hemiketals -gt fructose
In solution mainly in pyranoside form (67) In
combinations mostly found in furanose form
15
Carbohydrates
Monosaccharides
The anomeric center Carbonyl group is planar -gt
attack of OH from either side possible -gt 2
epimeric structures (anomers) Both anomers are in
equillibrium in solution
Epimers a -gt anomeric center highest chiral
center -gt different configuration (R,S
convention) Hydroxyl (OH) on anomeric C Down -gt
a-D-sugars and ß-L-sugars ß -gt anomeric center
highest chiral center -gt same configuration
(R,S convention) Up -gt ß-D-sugars and a-L-sugars
Epimer (Anomer)
Epimer (Anomer)
16
Carbohydrates
Monosaccharides
The anomeric center Carbonyl group is planar -gt
attack of OH from either side possible -gt 2
epimeric structures (anomers) Both anomers are in
equillibrium in solution
Epimers ß -gt anomeric center highest chiral
center -gt same configuration (R,S convention) a
-gt anomeric center highest chiral center -gt
different configuration
R,R-gt ß
S,R-gt a
17
Carbohydrates
Monosaccharides
The anomeric center Carbonyl group is planar -gt
attack of OH from either side possible -gt 2
epimeric structures (anomers) In solution -gt all
4 forms in equillibrium !!!
Aldohexoses
Ketose
18
Carbohydrates
Monosaccharides
The anomeric center Esterfication -gt freezes
sugar in its anomeric form (no interconvertion
between a and ß any more)
19
Carbohydrates
Monosaccharides
Alditols Reduction of sugars -gt reducing agent
(NaBH4) -gt reduces aldehydes ketons Reduction
occurs at small amount of open chain form -gt
shift in equilibrium -gt total reduction
achieved Reduction of Aldoses -gt 1 product
(primary alcohol) -gt Alditols Reduction of
Ketoses -gt 2 products (secondary alcohol) -gt
Alditols
20
Carbohydrates
Monosaccharides
Glycosides (replace suffix ose with oside) -gt
Reaction at C1 (anomeric C) Hemiacetals Alcohol
-gt Acetals (Glycoside) Hemiketals Alcohols -gt
Ketals (Glycoside)
OH on the anomeric C1
21
Carbohydrates
Monosaccharides
Glycosides (replace suffix ose with
oside) Hemiacetals Alcohol -gt Acetals
(Glycoside) Hemiketals Alcohols -gt Ketals
(Glycoside)
22
Carbohydrates
Monosaccharides
Glycosides (replace suffix ose with oside) -gt
Reaction at C1 Hemiacetal/Hemiketal Alcohol -gt
O- Glycoside -gt Polysaccharides Hemiketal/Hemiketa
l Amine -gt N-Glycoside
23
Carbohydrates
Monosaccharides
Glycosides (replace suffix ose with
oside) Hemiacetal/Hemiketal Alcohol -gt O-
Glycoside -gt Polysaccharides Hemiketal/Hemiketal
Amine -gt N-Glycoside
Template for aspirin
Nucleotides of RNA and DNA
24
Carbohydrates
Monosaccharides
Glycosides (replace suffix ose with
oside) Glucose MeOH -gt Acetal --? reaction
works directly Glucose complex alcohol -gt not
that easy
Example Production of salicin -gt Template for
Aspirin
25
Carbohydrates
Monosaccharides
Glycosides (replace suffix ose with
oside) Glucose MeOH -gt Acetal --? reaction
works directly Glucose complex alcohol -gt not
that easy
Example Production of salicin -gt Template for
Aspirin
26
Carbohydrates
Monosaccharides
Cyclic Acetals Ketals -gt protecting groups
2 OH groups are cis conformation -gt reaction with
keton
C6
27
Carbohydrates
Monosaccharides
Modified sugars -gt in cell membranes
28
Carbohydrates
Oligosaccharides -gt a few monomers
Found in dietary products
29
Carbohydrates
Polysaccharides
In Plant cell wall -gt cotton
In animal and plant cells
30
Carbohydrates
Polysaccharides
Glycogen -gt mammalian sugar storage
31
Carbohydrates
Polysaccharides
Starch amylose amylopectine -gt main
plant food reserve
32
Carbohydrates
Polysaccharides - Hydrolysis

• Chemically - under harsh conditions with hot
  acid -gt monosaccharides (glucose)
• - under mild
  conditions with acid -gt oligosaccharides
  (randomly)
• 2. Enzymatic very specific hydrolysis
• -gt a-amylase -gt
  hydrolysis a 1 -gt 4 bonds in starch (mainly
  maltose glucose)
• -gt a-1,6-glucosidase -gt
  hydrolysis a 1 -gt 6 bonds in starch
• -gt lactase -gt hydrolysis
  lactose
• (high activity of
  enzyme in infants low activity in adults -gt
  intolerance)
• -gt cellulase -gt
  hydrolysis ß 1 -gt 4 bonds -gt animals do not have
  it (need bacteria)

33
Carbohydrates
Oxidation of sugars
Under mild conditions -gt with cupric ion
(Fehlings solution) or Br2 -gt oxidation of
aldehyde group -gt acid (aldonic acid) If sugars
are glycosidic linked (acetal formation) -gt
aldehyde group not available for oxidation -gt no
reducing sugars If sugar are free -gt reducing
sugars
34
Carbohydrates
Oxidation of sugars
Under strong conditions -gt with HNO3 -gt oxidation
of aldehyde group alcohol groups (primary
alcohol) -gt diacid (aldaric acid)
35
Carbohydrates
Oxidation of sugars
Determination of glucose level in blood or urine
-gt oxidation of glucose gt H2O2 involved in
second reaction -gt colorimetric or voltametric
sensor (Biosensor) Diabetes mellitus Insulin
deficiency Insulin regulates blood sugar
(glucose) level If glucose level is high -gt
insulin level increases -gt prevents break down of
glycogen into glucose and conversion of fat or
protein into glucose -gt blood glucose level will
sink again If glucose level is low -gt insulin
level drops -gt more glucose produced -gt blood
glucose level will rise
36
Carbohydrates
Oxidation of sugars
Also oxidized by most enzymes
Terminal OH group oxidized in Aldoses -gt Uronic
acids
Pectins in cell walls of fruits -gt acid
solutions form gels -gt jam making
37
Carbohydrates
Oxidation of sugars
Terminal OH group oxidized in Aldoses -gt Uronic
acids
Pain reliefer
Even stronger pain reliefer
Morphine metabolism in human body -gt make it more
soluble -gt excretion
38
Carbohydrates
Oxidation of sugars
Vitamin C most animals can synthesize Vitamin C
Humans and primates cannot NOT
-gt synthesized in liver from glucose Essential
for - formation of structural proteins in skin,
bones, ligaments -
cofactor in synthesis reactions of amino acids
and modifications -
antioxidants
Deficiently (scurvy) -gt muscular pain, skin
lesions, fragile blood vessel, bleeding gums,
tooth loss
39
Carbohydrates
Aminosugars
Replacement of one OH group by a amino group In
nature -gt done by enzymes -gt 2-amino-2-deoxy
sugars
Chitin insect skeleton and shells of crustaceans
40
Carbohydrates
Aminosugars
Replacement of one OH group by a amino group In
nature -gt done by enzymes -gt 2-amino-2-deoxy
sugars
Bacterial cell walls -gt glycycosidic bond cleaved
by lysozyme
Lysozyme
ß-lactam antibiotics -gt inhibit peptidase linking
peptide bond during biosythesis of cell wall
41
Carbohydrates
Aminosugars
Replacement of one OH group by a amino group In
nature -gt done by enzymes -gt 2-amino-2-deoxy
sugars
Blood groups Determined by glycoproteins