Clase 7 Reactions of CHO

REACCIONES DE
CARBOHIDRATOS
Reactions of monosaccharides
• Carbonyl reactions:
•
•
•
•
•
•
•
Osazone formation
Cyanohydrin reaction
Reduction
Oxidation
Action of base
Action of acid
Ring chain tautomerism
• Alcohol reactions:
• Glycoside formation
• Ether formation
• Ester formation
Mutarrotación
Glucosa (Dextrosa);
Dextrosa);
Dextro--rotatoria
Dextro
rotatoria..
3
Mutorrotación
D-glucosa
glucosa::
Cicla de 2 formas → Estructuras
Furanosas o Piranosas.
Piranosas.
D-Ribose (C
(C--5): Estructuras
Furanosa o Piranosa
Conformaciones Silla o Bote de una estructura Piranosa.
Piranosa.
2 possible chair conformations
of β-D-glucose
Epimerización
H de C2 Removido → Ión Enolate.
Enolate.
Reprotonación:: Δ Estereoquímica de C2.
Reprotonación
8
Rearreglo Enodiol
• En medio Básico:
Básico: La posición del C=O puede Cambiar.
Cambiar.
• Los CHOs deben permanecer en slns ácidas o neutras
para preservar su identidad
identidad..
9
Reducción
• Puede ser:
– Cataliticamente: NaBH4
(H2/Ni,Pt,Pd)
– Enzimaticamente.
o
(H2
+
Catalizador)
• Productos : Polioles o Alco- Azucares (Alditoles)
• En general; se nombran adicionando la
terminación itol a la raíz del nombre del azúcar.
– Glucosa → Sorbitol (Glucitol)
– Manosa → Manitol
– Fructosa → Manitol + Sorbitol
– Gliceraldehido → Glicerol
ALDITOLES
Rxs Oxidación
Aldosas oxidadas → 3 9pos de ácidos
– Ácidos Aldónicos
Aldónicos:: Aldehído → Carbonilo (Glucosa →
ácido glucónico
glucónico))
– Ácidos Uronicos
Uronicos:: Aldehído permanece intacto ⇒ Se
oxida el primer alcohol del otro extremo de la
molécula..
molécula
• Glucosa → Ácido Glucuronico
• Galactosa → Ácido Galacturonico
– Ácidos Sacáricos (ácidos glicáricos
glicáricos)) – Oxidación en
ambos extremos de un monosacárido
monosacárido))
• Glucosa → Ácido Sacárico
• Galactosa → Ácido Múcico
• Manosa → Ácido Manárico
Oxidación con Bromo
• El agua de bromo oxida el aldehído formando
un Ácido Aldónico.
Chapter 23
14
Oxidación con Ácido Nítrico
• Oxida el aldehído y el alcohol terminal.
• Forma ácido aldárico.
15
Oxidación con Reactivo de Tollens.
Tollens.
• Reactivo de Tollens Rx con el aldehído, pero el
álcali del medio promueve el rearreglo enodiol,
así Rxnan también las cetosas.
plata.
• Azucares reductores forman un espejo de plata
Chapter 23
16
Formas Oxidadas DD-Glucosa
Azucares no Reductores
• Glicósidos son acetales, estables a álcalis, no
dan fácilmente reacciones de oxidación.
• Disacáridos y Polisacáridos son también acetales
y azucares no reductores.
18
Formation of Glycosides
• React the sugar with alcohol in acid.
• Since the open chain sugar is in equilibrium
with its α- and β-hemiacetal, both anomers of
the acetal are formed.
• Aglycone is the term used for the group bonded
to the anomeric carbon.
=>
Chapter 23
19
Ether Formation
• Sugars are difficult to recrystallize from water
because of their high solubility.
• Convert all -OH groups to -OR, using a modified
Williamson synthesis
synthesis, after converting sugar to
acetal, stable in base.
20
Ester Formation
Acetic anhydride with pyridine catalyst converts
all the oxygens to acetate esters.
21
Formation of osazones
• Identification of sugars.
sugars.
Phenylhydrazine..
• Rx Monosaccharide + Phenylhydrazine
• A crystalline compound with a sharp melting point will
be obtained
obtained..
• D-fructose and D-mannose
Osazone as D-glucose
glucose..
• Seldom used for identification
identification;; we now use HPLC or
mass spectrometry.
spectrometry.
Osazone Formation
Both C1 and C2 react with phenylhydrazine.
23
Ruff Degradation
Aldose chain is shortened by oxidizing the
aldehyde to -COOH
COOH,, then decarboxylation
decarboxylation..
25
Ruff degradation
Series of reactions that removes the reducing carbon ( C=O ) from
a sugar and decreases the number of chiral centers by one;
one; used to
relate configuration.
configuration.
CHO
H
OH
H
OH
CH 2 O H
Br 2
H 2O
CO 2 H
H
OH
H
OH
CH 2 O H
Ca 2+
CHO
H
OH
CH 2 O H
D-(+)-glyceraldehyde
H 2O 2
Fe 3 +
CO 2
H
OH
H
OH
CH 2 O H
Cyanohydrin formation
• Rxn Aldose + HCN
• Used to increase the chain length of
monosaccharides
• Results in a Cyanohydrin
hydrolyzed
Acid
Reduced
Aldehyde..
Aldehyde
• Known as the Fischer
Fischer--Kiliani synthesis
• Can prepare all monosaccharides from Dglyceraldehyde
Kiliani--Fischer synthesis.
Kiliani
Series of reactions that extends the carbon chain in a CHO by one
carbon and one chiral center.
CHO
HCN
H
OH
CH2OH
C N
C N
COOH
COOH
H
H
OH HO
+,H O
H
2 H
OH HO
H
+ H
OH
H
OH
H
OH H
OH
CH2OH
CH2OH
CH2OH
CH2OH
CHO
H
OH
H
OH
CH2OH
diastereomers
separable
Na(Hg)
O C
H
OH
H
OH
H2C
O
lactone
-H2O
Kiliani--Fischer Synthesis
Kiliani
• This process lengthens the aldose chain.
• A mixture of C2 epimers is formed.
29
Periodic Acid Cleavage
• Periodic acid cleaves vicinal diols to give two
carbonyl compounds.
• Separation and identification of the products
determine the size of the ring.
30
Base-catalyzed isomerisation of
monosaccharides
H
O
H
HO
H
H
OH
H
OH
OH
CH2OH
Glucose
Enolization
H
OH
OH
HO
H
H
OH
H
OH
CH2OH
Ca(OH)2
H2O
H
O
H
O
H
HO
H
H
OH
H
OH
OH
CH2OH
HO
HO
H
H
H
H
OH
OH
CH2OH
+
Recovered glucose, 67%
CH2OH
+
Mannose, 2%
O
HO
H
H
OH
H
OH
CH2OH
Fructose, 30%
Glycosides
Glycoside formation
A glycoside hydroxyl
CH2OH
OH
H
H
OH H
HO
OH
H
OH
α-D-Glucopyranose (a hemiacetal)
CH2OH
OO
H
H
OH H
HO
H
H
OH
HCl, CH3OH
CH3
+
CH2OH
OH
H
H
OH H
HO
O
CH3
H
OH
Methyl β-D-glucopyranoside (a glycoside (an acetal)
+
H
CH2OH
OH
H
H
OH H
+
HO
O
H
H
OH
H
CH3
CH2OH
O
H
+
H
OH H C H
HO
H
OH
O
HO
CH3
CH2OH
CH2OH +
OH
OO
H
H
H
H
H+
OH H
OH H
+
HO
HO
H
O
H
OH
H
OH
O
OH
CH2OH
Another example of a glycoside:
OH
H3CO
OH H
O
O
H
H
Doxorubicin (an anticancer drug)
H
CH3
HO
O
H
NH2
1. Alkylation at the glycoside position.
H
CH3
2. Complete alkylation
OH
OH
HO
HH H
H
OH
OH OH
OCH3
H3CO
OH
(CH3O)2SO2
HH H
H
OCH3
NaOH
OCH3
H3CO
+
OCH3
H3CO
OOCH3
HH H
H
H
OCH3
OCH3
3. Complete acylation
OH
OAc
AcO
O
OH
HO
H Acetic anhydride
HH H
HH H
H
OH
H
OAc
Py
OH OH
OAc
AcO
+
OAc
AcO
OOAc
HH H
H
H
OAc
OAc
N y C Glycoside Formation
OH
OH
O OH
H
H
CH3OH
O CH
3
H
H
OH
H
OH
HO
H
H
H+
H
HO
H
H
OH
•Stable in water
•Does not undergo
mutorotation
OH
Acetal
Hemi-acetal
O
OH
O
O OH
H
NH
H
OH
H
HO
OH
NH
NH
O
OH
O
H
OH
H
H
N
O
H
H
HO
H
H
OH
N-glycoside
Glucose oxidase
• Glucose oxidase converts glucose to gluconic acid
and hydrogen peroxide
• When the reaction is performed in the presence of
peroxidase and O-Dianisidine a yellow color is
formed
• This forms the basis for the measurement of urinary
and blood glucose
• Testape
Testape,, Clinistix,
Clinistix, Diastix (urinary glucose)
• Dextrostix (venous glucose)
Glycoconjugates..
Glycoconjugates
Formation of spans and tweens
OH
CH2
O
SORBITOL
CH
OH
OH
THF compound
OH
1,4-SORBITAN
O
O
CH2 O
O
C
CH2 (O-C2H4) O C R
R
O
CH (O-C2H4)nOH
CH
OH
HO (C2H4-O)x
OH
(O-C2H4)x OH
OH
SPANS (form W/O emulsions)
TWEENS (form O/W emulsions)
Action of strong acids on monosaccharides
• Monosaccharides are normally stable to dilute
acids, but are dehydrated by strong acids
• D-ribose when heated with concentrated HCl
yields furfural (commercial route for the
production of THF (tetrahydrofuran
tetrahydrofuran))
• D-glucose under the same conditions yields 5hydroxymethyl furfural
Action of base on sugars
• Sugars are weak acids and can form salts at
high pH.
pH.
• A 1,2-enediol salt is formed as the result.
result.
• This allows the interconversion of D-mannose,
D-fructose and D-glucose
glucose..
• The reaction is known as the Lobry de Bruyn
Bruyn-Alberta von Eckenstein Reaction.
Reaction.
Action of base on sugars
• Enediols obtained by the action of base are quite susceptible
to oxidation when heated in the presence of an oxidizing
agent
• Copper sulfate is frequently used as the oxidizing agent and a
red preciptate of Cu2O is obtained
• Sugars which give this reaction are known as reducing sugars
• Fehling’s solution : KOH or NaOH and CuSO4
• Benedict’s solution: Na2CO3 and CuSO4
• Clinitest tablets are used to detect urinary glucose in diabetics
Glucose measurement methods
• Most methods are enzymatic methods
– 3 enzyme systems are currently used to measure glucose:
• Glucose oxidase
• Glucose dehydrogenase
• Hexokinase
• These reactions produce either a product that can be
measured photometrically or an electrical current
that is proportional to the initial glucose
concentration
Glucose dehydrogenase methods
α -D-glucose
mutarotase
β -D-glucose + NAD
ΜΤΤ + NADH
β -D-glucose
glucose dehydrogenase
diaphorase
D-gluconolactone + NADH
MTTH (blue color) +NAD
glucose dehydrogenase
Gluconolactone + PQQH
glucose + pyrroloquinoline quinone (PQQ)
PQQH
2
+ 2[Fe(CN) 6 ] -3
2[Fe(CN) 6 ] -4
PQQ + 2[Fe(CN)
2[Fe(CN) 6 ] -3 + 2e -
6]
-4
+ 2H +
Glucose oxidase methods:
colorimetric method
glucose oxidase
β -D-glucose + O 2
D-gluconolactone + H 2O 2
D-gluconolactone + H 2O
gluconic acid
H 2O 2 + chromogenic oxygen acceptor (ortho-dianisidine, 4 aminophenazone, ortho-tolidine)
peroxidase
colored chromogen + H 2O
Glucose oxidase methods:
electronic sensing method
β -D-glucose +
2[Fe(CN) 6
]-3
glucose oxidase
+ H 2O
2[Fe(CN) 6]-4
D-gluconic acid +
2[Fe(CN) 6]-4 + 2H +
2[Fe(CN) 6]-3 + 2e -
glucose oxidase
β -D-glucose + O 2
H 2O 2
D-gluconolactone + H 2O 2
2H + + O 2 + 2e -
A blood test for glucose levels
Dye
H
C
H
HO
O2
Colored Dye
OH
H2O2
O
C
OH
H
H
Glucose Oxidase
HO
O
OH
H
H
OH
H
OH
H
OH
H
OH
CH2OH
D-Glucose
CH2OH
D-Gluconic Acid
(An Aldonic Acid)
An example of an enzymatic oligosaccharide synthesis
used for the production of a clinical candidate
OH OH
O
HO
OH
HO
NHAc
HO
O
CMP-Sialic acid
OR
O
OH
α2,3-Sialyltransferase
HO
AcHN
CO2–
OH
O
OH OH
O
O
NHAc
HO
O
OH
HO
N-Acetyllactosamine
(from chemical synthesis)
GDP-Fucose
α 1,3-Fucosyltransferase
OH
OH
HO
HO
AcHN
CO2–
OH
O
HO
H3C
OH OH
O
NHAc
O
O
O
O
OH
OH
O
OH
OR
Sialyl Lewis x: An anti-inflammatory agent developed by Cytel
O
OH
OR
Present limitations of enzymatic oligosaccharide synthesis:
1. The nucleotide sugars are expensive
2. Not all enzymes are available in recombinant form
3. The enzymes do not accept many unnatural sugars,
thus modified oligosaccharides cannot be readily made
4. Most glycosyltransferases are inhibited by high concentrations
of the nucleotide product; thus, large scale synthesis is difficult
Many groups are seeking solutions to these problems
so stay tuned!….
The present challenge:
Integrating oligosaccharide synthesis with protein
chemistry to make glycoproteins
OH
OH
H3C
OH OH
O
OH
HO OH
NHAc
CO2–
O
O
HO
O
O
O
O
O
AcHN
OH
OH
HO
OH OH
HO
HO OH CO2–
O
O
O
HO
O
O
AcHN
AcHN O
HO
HO
N
H
CH3(H)
O
Chemical synthesis of carbohydrates is important for…
• Studying their biological activities
• Development of new therapeutic compounds
Examples of approved carbohydrate drugs:
Substance
Acarbose
AMVISC
Hyalgan
Lovenox
Miglitol
ORTHOVISC
Relenza
Tamiflu
SOLARASE
Topamax
Voglibose
Indication
Diabetes
Opthalamic surgery
Osteoarthritis
Cardiovascular disease
Diabetes
Osteoarthritis
Influenza
Influenza
Actinic keratosis
Epilepsy
Diabetes
Company
Bayer AG
Anika Therapeutics
FIDIA/Sanofi
Aventis
Bayer AG
Anika Therapeutics
Glaxo Smithkline
Roche
Hyal Pharmaceuticals
J&J
Takedo/Abbott
Modificación del Almidón
Almidón
Modificación Física:
Física: Modificación Química:
Pregelatinización
Enlaces cruzados ((cross
cross linked
linked))
Dextrinización
Esterificados
Hidroxialkilados
Fosfato monoesterificados
Xantatos
Dextrinización
Jarabe de glucosa
Modificación
Biotecnológica:
Dextrinización
Jarabe de glucosa
Jarabe de glucosaglucosafructosa