1.3 (Fig. 6) Since terminal Alkynes are fairly unreactive


1.3 Synthetic routes of 1,2,3-
triazole ring system
ring  system  could 
be prepared by different synthetic methodologies 

1-  1,3-Dipolar cycloaddition reactions of azides

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2-  The Copper-Catalyzed
Azide-Alkyne Cycloaddition (CuAAC)

3-  The Ruthenium-Catalyzed
Azide-Alkyne Cycloaddition (RuAAC)


 1.4 Click Chemistry

  The click chemistry approach invented by Sharpless 29using
copper (I)-catalyzed azidealkyne cycloaddition (CuAAC) has resulted in the
production of large number of 1, 4-disubstituted 1, 2, 3-triazoles in very high
yields 30. The copper(I)-catalyzed azidealkyne cycloaddition
(CuAAC) approach has been widely used in the different spheres of the science
such as bioconjugation 31,oligonucleotide synthesis 32, construction of bolaamphiphilic
structures 33, DNA labelling 34 and
drug discovery 35. In the present scenario of a continuous
requirement for better drugs in shorter times, it is a challenging task to
prepare new molecules that combine high activity and selectivity, drug-likeness
and good pharmacokinetic properties. Figure 5

Figure 5 Synthetic routes of 1,2,3- triazole


most prominent example of click chemistry is the Cu(I)-catalyzed Azide-Alkyne
Click Chemistry (CuAAC) reaction36. An Azide-functionalized molecule A reacts
with a terminal Alkyne-functionalized 
molecule B thereby forming a stable conjugate A-B via a Triazole moiety
(Fig. 6) Since terminal Alkynes are fairly unreactive towards Azides, the
efficiency of a CuAAC reaction strongly depends on the presence of a metal
catalyst such as copper (Cu) in the +1 oxidation state (Cu(I)). Different
copper sources and reduction reagents are available however, the Cu(II) salt
CuSO4 as copper source in combination with ascorbate as a reduction reagent has
been recommended for most biomolecule labeling applications


Figure 6  Principle of
Cu(I)-catalyzed Azide-Alkyne Click            Chemistry(CuAAC).