Recent Developments in the Synthesis of Indole-Pyrazole Hybrids

Indole and pyrazole are two important scaffolds in the field of medicinal chemistry. Compounds bearing indole and/or pyrazole moiety have been extensively investigated for a wide range of biological applications. Of them, compounds containing both indole and pyrazole moieties (also termed as indole-pyrazole hybrids) are of particular interest since synergistic pharmacological activities may be gained comparing to those with each individual pharmacophore. Indole-pyrazole hybrids can be classified into two general classes of direct-linked hybrids and spacer-linked hybrids. For each class, it can be sub-divided into indole-C2 pyrazole hybrids, indole-C3 pyrazole hybrids and indole-C4/5/6/7 pyrazole hybrids based on the substitution position of pyrazole on the indole moiety. Many types of indole-pyrazole hybrids have been reported with good antimicrobial, anticancer, antitumor, anti-inflammatory, anti-oxidant activities etc. However, no papers have been noted to comprehensively summarize the chemical synthesis of these important indole-pyrazole hybrids as bioactive compounds except for a few reviews focusing on the synthesis of each individual indole- and pyrazole-containing derivatives. Thus, we here present a comprehensive and updated review focusing on the progress of chemical synthesis of all types of indole-pyrazole hybrids in order to provide a better understanding of the indole-pyrazole hybrids to researchers in the fields of synthetic chemistry and to facilitating drug development.