1

CATALYTIC AZIDE-ALKYNE CYCLOADDITION: REACTIVITY AND

APPLICATION

PREET PAL SINGH SIDHUGRADUATE STUDENTDEPT.OF MEDICINAL CHEMISTRYSCHOOL OF PHARMACY, VCU

For more presentations and information visit http://www.pharmaxchange.info

2

OVERVIEW

Introduction Mechanism Source of catalyst Auxiliary ligands One pot synthesis Microwave assisted CuAAC CuAAC of sulfonyl azide Potential problems Applications Conclusion

For more presentations and information visit http://www.pharmaxchange.info

3

INTRODUCTION

Most suited reaction of CLICK CHEMISTRY Selective reaction to form hetero-link.

Sharpless et al. Angew. Chem. Int. Ed. 2001, 40, 2004

R2

+NN -N

R1

+N

NN

R2

1,4

Cu catalystrt, mins-hours

R1N

NN

R2

R12

3

45

1

R2

+NN -N

R1

+N

NNN

NN

R2R2

R1R1

1,4 1,5

+60-120 0C

Hours-days

Huisgen thermal 1,3-cycloaddition

CuAAC

∆H= -45 kcal/mol

For more presentations and information visit http://www.pharmaxchange.info

4

CHARACTERISTIC OF CuAAC

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

For more presentations and information visit http://www.pharmaxchange.info

5

PROPERTIES OF REACTANTS

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.

R2

+NN -N

R1

+N

NN

R2

1,4

Cu catalystrt, mins-hours

R1

For more presentations and information visit http://www.pharmaxchange.info

6

ADVANTAGES OF 1,2,3-TRIAZOLE

High chemical stability. Strong dipole moment (5.2-5.6D). Good hydrogen bond acceptor. An alternative for amide linkage.

Sharpless et al. Drug Discov. Today, 2003, 8, 1128

NN

N1

R2

R12

3

45

For more presentations and information visit http://www.pharmaxchange.info

7

MECHANISM

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

For more presentations and information visit http://www.pharmaxchange.info

8

MECHANISM

Maarseveen et al. Eur. J. Org. Chem. 2006, 1, 51

R2 H+

LnCu [LnCu]2

CumLnR2 H B B-H

LnCu2 R2

R1-N3

R2

CuILLCuI

1N-R1

+N

N3

L L

CuI1N

R1

N

N

R2

N3N1NR1

R2LnCu2

B-H B

N3N1NR1

R2H

CuI

For more presentations and information visit http://www.pharmaxchange.info

9

GENERATION OF Cu(I) CATALYST

Direct addition of Cu(I) salts. Reduction of Cu(II) salts. Oxidation of Cu metal. Comproportionation of Cu(0) and Cu(II).

For more presentations and information visit http://www.pharmaxchange.info

10

DIRECT ADDITION OF Cu(I) SALT

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.

For more presentations and information visit http://www.pharmaxchange.info

11

DIRECT ADDITION OF Cu(I) SALT

Wong et al J. Am. Chem. Soc. 2002, 124, 14397

For more presentations and information visit http://www.pharmaxchange.info

12

REDUCTION OF Cu (II) SALT

Example: Cu sulfate pentahydrate, Cu acetate etc.

Sodium ascorbate is used as reductant. No inert atmosphere requirement. Economical. Thermodynamically stable. High yield and purity.

For more presentations and information visit http://www.pharmaxchange.info

13

REDUCTION OF Cu (II) SALT

Fokin et al Angew. Chem. Int. Ed. 2002, 41, 2596

For more presentations and information visit http://www.pharmaxchange.info

14

OXIDATION OF Cu METAL

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.

For more presentations and information visit http://www.pharmaxchange.info

15

OXIDATION OF Cu METAL

Sharpless et al J. Am. Chem. Soc. 2005, 127, 210

For more presentations and information visit http://www.pharmaxchange.info

16

COMPROPORTIONATION METHOD

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

For more presentations and information visit http://www.pharmaxchange.info

17

AUXILIARY LIGANDS

Examples: TBTA Sulfonated bathophenanthroline Pybox Accelerate the rate of CuAAC. Sequester copper ions and hence prevent

damage to bio-molecules. Best suited for bioconjugation process.

For more presentations and information visit http://www.pharmaxchange.info

18

AUXILIARY LIGAND

TBTA

Sulfonated bathophenanthroline

N N

NaO3S SO3Na

Pybox

N

NN

N

NN

N

N

N N

Ph

Ph

Ph

For more presentations and information visit http://www.pharmaxchange.info

19

ONE POT MULTI-STEP SYNTHESIS

Overcome safety problem of low MW azide. Azide is generated in-situ.

For more presentations and information visit http://www.pharmaxchange.info

20

ONE POT MULTI-STEP SYNTHESIS

Wang et al Tetrahedron Lett. 2005, 46, 2331

For more presentations and information visit http://www.pharmaxchange.info

21

MICROWAVE-ASSISTED CuAAC

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.

R2N

NN1

R2

R1

1,4

NaN3 +R X +Cu(0), CuSO4

BuOH, MW, 10-15 MIN

For more presentations and information visit http://www.pharmaxchange.info

22

MICROWAVE-ASSISTED CuAAC

For more presentations and information visit http://www.pharmaxchange.info

23

REACTION OF SULFONYL AZIDE

Different product in different condition. Amidine, Amide, Azetidin-2-imines and

Triazole can be formed.

For more presentations and information visit http://www.pharmaxchange.info

24

REACTION OF SULFONYL AZIDE

Amidine

Amide

Azetidinimine

Triazole

For more presentations and information visit http://www.pharmaxchange.info

25

REACTION OF SULFONYL AZIDE

amine

For more presentations and information visit http://www.pharmaxchange.info

26

WHEN CLICK CHEMISTRY FAILS

Binding problem for highly electron deficient azide.

Alkyne homocoupling. Cu(I) saturation by polyalkyne.

Diederich et al Angew. Chem. Int. Ed. 2000, 39, 2632

For more presentations and information visit http://www.pharmaxchange.info

27

ALKYNE HOMOCOUPLING

Diederich et al. Angew. Chem. Int. Ed. 2000, 39, 2632

For more presentations and information visit http://www.pharmaxchange.info

28

Cu(I) SATURATION

Zhou et al. Org. Lett. 2005, 7, 1035

For more presentations and information visit http://www.pharmaxchange.info

29

APPLICATIONS OF CuAAC

Synthesis of small molecule screening libraries.

Synthesis of glycoconjugate. Modification and biological profiling of

natural products. Bioconjugation. Synthesis of functional dendrimers.

For more presentations and information visit http://www.pharmaxchange.info

30

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.

For more presentations and information visit http://www.pharmaxchange.info

SYNTHESIS OF SCREENING LIBRARIES

a) NaN3, EtOH/H20 60 °C, 2 h; b) 4 N HCl/dioxane; c) (S)-3-tetrahydrofuranyl 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.

For more presentations and information visit http://www.pharmaxchange.info

32

SYNTHESIS OF SCREENING LIBRARIES

Wong et al ChemBioChem. 2003, 4, 1246

For more presentations and information visit http://www.pharmaxchange.info

SYNTHESIS OF SCREENING LIBRARIES

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

Enzyme IC50 [nM] Ki [nM] IC50 [nM] Ki [nM]

11

2

3

4

4

For more presentations and information visit http://www.pharmaxchange.info

34

MODIFICATION AND BIOLOGICAL PROFILING OF NATURAL PRODUCTS

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.

For more presentations and information visit http://www.pharmaxchange.info

35

MODIFICATION AND BIOLOGICAL PROFILING OF NATURAL PRODUCTS

Zhang et al Org. Lett. 2005, 7, 1513

For more presentations and information visit http://www.pharmaxchange.info

MODIFICATION AND BIOLOGICAL PROFILING OF NATURAL PRODUCTS

11µg/ml

7µg/ml 13µg/ml

24µg/ml

10µg/ml

For more presentations and information visit http://www.pharmaxchange.info

37

SYNTHESIS OF GYLCO-CONJUGATE

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.

For more presentations and information visit http://www.pharmaxchange.info

38

SYNTHESIS OF GYLCOCONJUGATE

Groothuys et al, Org. Lett. 2004, 6, 3123

Acetylene glycoside

For more presentations and information visit http://www.pharmaxchange.info

39

BIOCONJUGATION

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.

For more presentations and information visit http://www.pharmaxchange.info

40

BIOCONJUGATION

Wang et al Org. Lett. 2004, 6, 4603

For more presentations and information visit http://www.pharmaxchange.info

41

SYNTHESIS OF DENDRIMERS

Highly ordered, regularly branched, globular macromolecule.

Ideal for creating bioactive nanomaterials and for sensor application.

Currently 3rd generation are synthesized.

For more presentations and information visit http://www.pharmaxchange.info

42

SYNTHESIS OF DENDRIMERS

Sharpless et al Chem. Commun. 2005, 5775

For more presentations and information visit http://www.pharmaxchange.info

43

CONCLUSION

Catalytic azide-alkyne cycloaddition offers an alternate method for cycloaddition reactions

For more presentations and information visit http://www.pharmaxchange.info