Transcript CATALYTIC AZIDE-ALKYNE CYCLOADDITION:REACTIVITY AND

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CATALYTIC AZIDE-ALKYNE
CYCLOADDITION: REACTIVITY
AND APPLICATION
PREET PAL SINGH SIDHU
GRADUATE STUDENT
DEPT.OF MEDICINAL CHEMISTRY
SCHOOL OF PHARMACY, VCU
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OVERVIEW
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Introduction
Mechanism
Source of catalyst
Auxiliary ligands
One pot synthesis
Microwave assisted CuAAC
CuAAC of sulfonyl azide
Potential problems
Applications
Conclusion
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INTRODUCTION
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Most suited reaction of CLICK CHEMISTRY
Selective reaction to form hetero-link.
Huisgen thermal 1,3-cycloaddition
+
N N
-
R1
N
+
60-120 0C
R1
N
N
R1
N
+
Hours-days
R2
N
N
N
∆H= -45 kcal/mol
R2
R2
1,5
1,4
CuAAC
+
N N
-
+
N
R1
R1
Cu catalyst
rt, mins-hours
N
N
R2
3
2
R1
N
R2
1N
5
N
N
4
3
R2
1,4
Sharpless et al. Angew. Chem. Int. Ed. 2001, 40, 2004
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CHARACTERISTIC OF CuAAC
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Not affected by steric and electronic
properties of functional groups.
Can be carried out in both water and
organic solvents.
Rate is 107 faster than uncatalyzed.
High regioselectivity.
Minimal work-up and purification.
Least affected by temperature and pH.
Fokin et al. Aldrichimica Acta, 2007,40,7
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PROPERTIES OF REACTANTS
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Alkyne and azide is reactive and selective.
Organic azides are stable and safe to use.
Low molecular wt azides are unsafe to use.
Electron deficient azides gives poor yield.
Electron rich alkynes are not reactive.
+
N N
-
+
N
R1
R1
Cu catalyst
rt, mins-hours
N
N
R2
R2
1,4
5
N
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ADVANTAGES OF 1,2,3-TRIAZOLE
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High chemical stability.
Strong dipole moment (5.2-5.6D).
Good hydrogen bond acceptor.
An alternative for amide linkage.
2
R1 N
3
N1
N
5
4
R2
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Sharpless et al. Drug Discov. Today, 2003, 8, 1128
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MECHANISM
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Thermal cycloaddition occurs in concerted
fashion
CuAAC occurs in stepwise.
Cu(I) species is required.
Reaction is second order in copper.
Lower the activation barrier by 11 kcal/mol
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MECHANISM
R2
H
+
LnCu
2
R
[LnCu]2
N
H
R2
+
R1
N
1 -
1
N
LnCu2
N
N
R2
L
I
N Cu
1
R1
B-H
3
L
N
N
I
L
CuI L Cu
R1
R2
CuI
N
R1-N3
LnCu2
R2
3
8
B B-H
CumLn
B
R1
1
N
H
N
N3
R2
Maarseveen et al. Eur. J. Org. Chem. 2006, 1, 51
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GENERATION OF Cu(I) CATALYST
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Direct addition of Cu(I) salts.
Reduction of Cu(II) salts.
Oxidation of Cu metal.
Comproportionation of Cu(0) and Cu(II).
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DIRECT ADDITION OF Cu(I) SALT
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Examples: CuI, CuBr, and coordination
complexes like Cu(CH3CN)4PF6, (EtO)3P·CuI.
Thermodynamically unstable.
Nitrogen type donors prevent degradation.
Reliable catalyst in presence of base.
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DIRECT ADDITION OF Cu(I) SALT
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Wong et al J. Am. Chem. Soc. 2002, 124, 14397
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REDUCTION OF Cu (II) SALT
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Example: Cu sulfate pentahydrate, Cu
acetate etc.
Sodium ascorbate is used as reductant.
No inert atmosphere requirement.
Economical.
Thermodynamically stable.
High yield and purity.
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REDUCTION OF Cu (II) SALT
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Fokin et al Angew. Chem. Int. Ed. 2002, 41, 2596
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OXIDATION OF Cu METAL
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Require more Cu and long reaction time.
Cu(0) nanosize activated powder can be used.
Amine hydrochloride salts are used for
oxidative dissolution.
Acid sensitive group need to be protected.
Seven times costly.
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OXIDATION OF Cu METAL
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Sharpless et al J. Am. Chem. Soc. 2005, 127, 210
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COMPROPORTIONATION METHOD
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By comproportionation of Cu(II) and Cu(0).
Just a piece of copper wire is added.
Requires longer time.
Convenient for high throughput synthesis of
screening library.
Fokin et al Angew. Chem. Int. Ed. 2002, 41, 2596
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AUXILIARY LIGANDS
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Examples: TBTA
Sulfonated bathophenanthroline
Pybox
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Accelerate the rate of CuAAC.
Sequester copper ions and hence prevent
damage to bio-molecules.
Best suited for bioconjugation process.
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AUXILIARY LIGAND
Ph
N
N
N
N
N
N N
N
Ph
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Ph
NaO3S
N
N N
N
SO3Na
Sulfonated bathophenanthroline
TBTA
Pybox
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ONE POT MULTI-STEP SYNTHESIS
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Overcome safety problem of low MW azide.
Azide is generated in-situ.
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ONE POT MULTI-STEP SYNTHESIS
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Wang et al Tetrahedron Lett. 2005, 46, 2331
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MICROWAVE-ASSISTED CuAAC
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CuAAC requires no heating but microwave
reduces the time of reaction.
Reduces the undesired side reaction.
Reduces the catalyst loading.
Reduces the time of one pot synthesis to 15
min.
R1
R
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2
X + NaN3 + R
Cu(0), CuSO4
BuOH, MW,
10-15 MIN
N1
N
N
R2
1,4
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MICROWAVE-ASSISTED CuAAC
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REACTION OF SULFONYL AZIDE
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Different product in different condition.
Amidine, Amide, Azetidin-2-imines and
Triazole can be formed.
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REACTION OF SULFONYL AZIDE
Amidine
Amide
Azetidinimine
Triazole
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REACTION OF SULFONYL AZIDE
amine
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WHEN CLICK CHEMISTRY FAILS
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Binding problem for highly electron
deficient azide.
Alkyne homocoupling.
Cu(I) saturation by polyalkyne.
Diederich et al Angew. Chem. Int. Ed. 2000, 39, 2632
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ALKYNE HOMOCOUPLING
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Diederich et al. Angew. Chem. Int. Ed. 2000, 39, 2632
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Cu(I) SATURATION
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Zhou et al. Org. Lett. 2005, 7, 1035
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APPLICATIONS OF CuAAC
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Synthesis of small molecule screening
libraries.
Synthesis of glycoconjugate.
Modification and biological profiling of
natural products.
Bioconjugation.
Synthesis of functional dendrimers.
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SYNTHESIS OF SCREENING LIBRARIES
CuAAC is the ideal reaction for:
Synthesis of library for initial screening.
Structure-activity profiling.
What makes it ideal?
Works well in most of the solvents.
Doesn’t require inert atmosphere.
Results in cleaner isolated product.
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SYNTHESIS OF SCREENING LIBRARIES
a) NaN3, EtOH/H20 60 °C, 2 h; b) 4 N HCl/dioxane; c) (S)-3tetrahydrofuranyl N-oxysuccinimidyl carbonate, Et3N; d) i-BuNH2,
MeOH; e) p-methoxybenzenesulfonyl chloride, K2CO3, CH3CN, 3 h;
f) 4 N HCl/dioxane; g) TfN3, H2O/CH2Cl2/MeOH, RT.
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SYNTHESIS OF SCREENING LIBRARIES
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Wong et al ChemBioChem. 2003, 4, 1246
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SYNTHESIS OF SCREENING
LIBRARIES
4
1
1
2
3
4
Enzyme
IC50 [nM]
Ki [nM]
IC50 [nM]
Ki [nM]
HIV PR
6±0.5
1.7±0.1
13±0.5
4±0.5
V82F
19±1
10±0.5
24±1
13±0.5
G48V
39±1
22±1
17±1
9.7±0.5
V82A
46±2
27±1
52±2
30±1
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MODIFICATION AND BIOLOGICAL
PROFILING OF NATURAL PRODUCTS
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Many bioactive natural products have
narrow therapeutic window.
Modification is viable approach to
improve therapeutic index.
CuAAC is ideal reaction for last step
derivatization of complex bioactive
molecule.
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MODIFICATION AND BIOLOGICAL
PROFILING OF NATURAL PRODUCTS
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Zhang et al Org. Lett. 2005, 7, 1513
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MODIFICATION AND BIOLOGICAL
PROFILING OF NATURAL PRODUCTS
11µg/ml
7µg/ml
13µg/ml
24µg/ml
10µg/ml
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SYNTHESIS OF GYLCO-CONJUGATE
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Act as a mediator of complex cellular
events such as adhesion
inflammation,etc.
N- or O- glycosidic linkage are sensitive
to hydrolysis.
Alternative is stable and isosteric triazole
linkage by CuAAC.
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SYNTHESIS OF GYLCOCONJUGATE
Acetylene glycoside
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Groothuys et al, Org. Lett. 2004, 6, 3123
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BIOCONJUGATION
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For investigation of protein structure and
function in vivo.
Unnatural amino acid are incorporated
into proteome which allow tracking of
proteome dynamic to external stimuli.
Complement to gene labeling approach.
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BIOCONJUGATION
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Wang et al Org. Lett. 2004, 6, 4603
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SYNTHESIS OF DENDRIMERS
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Highly ordered, regularly branched,
globular macromolecule.
Ideal for creating bioactive nanomaterials
and for sensor application.
Currently 3rd generation are synthesized.
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SYNTHESIS OF DENDRIMERS
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Sharpless et al Chem. Commun. 2005, 5775
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CONCLUSION
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Catalytic azide-alkyne cycloaddition offers an
alternate method for cycloaddition reactions