Recent Highlights on the Synthesis of Pyrazoles with Antimicrobial Activity
Authors: Da Silva Caroline C. , Martins Rosiane M. , Lund Rafael G. , Pizzuti Lucas , Pereira Claudio M.P. de 
Published: July 2018

Background:
Heterocyclic compounds containing nitrogen atoms such as pyrazoles have a
long history and applicability in the field of medicinal chemistry. Many compounds containing pyrazole
moiety have been reported in the available literature for their prominent biological activities, including
antimicrobial activity against different microorganisms. Over the years, there has been a concern with
the many health problems associated with the dramatic increase of microbial infections and resistance to
standard drugs, so there is a need for the development of more effective antimicrobial agents. Pyrazoles
and their derivatives are promising candidates to bypass these problems with good safety profiles, and
there is a wide range of synthetic methodologies for their obtainment. This review aims to compact a
literature survey (2012-2017) very informative and helpful for researchers who wish to study or continue
the development of new, potent and broad-spectrum antimicrobial compounds.

Methods:
This review encompasses reports on the synthesis and antimicrobial evaluation of synthetic
pyrazoles from the year 2012 to 2017, which were extracted from bibliographic databases such as
PubMed, scielo, sciencedirect, scifinder, and scopus. The main keywords in our search were “pyrazole”
and “antimicrobial activity”, in which we made efforts to include synthetic and biological methodologies
that can be useful for laboratories of different levels of infrastructure. Moreover, inclusion/
exclusion criteria was applied to select quality reports which could demonstrate different tools of
antimicrobial evaluation, focusing on the advances made in the area, such as evaluation in silico and
exploration of the possible mechanism of action for active compounds.

Results:
Thirty-four papers were included in this work, which was displayed chronologically from the
year 2012 to 2017 in order to enhance the advances made in the area, with at least five reports from each
year. We found that the most commonly tested bacterial strains are Staphylococcus aureus, Escherichia
coli, Pseudomonas aeruginosa, Bacillus subtilis, and from the year 2016 onwards Mycobacterium tuberculosis.
The most common tested fungal strains are Candida albicans, Aspergillus flavus, and
Aspergillus niger. The majority of articles expressed the antimicrobial results as a zone of inhibition,
leading to the determination of the Minimum Inhibitory Concentration (MIC) and a probable mechanism
of action for the most prominent compounds, considering cytotoxicity. Aromatic aldehydes and
ketones are key reactants to obtain important precursors for the synthesis of pyrazoles, such as chalcones,
together with alkyl or phenylhydrazines and thiosemicarbazide. A great variation in the reported
MICs was found as there is no standard maximum limit, but many compounds exhibited antimicrobial
activity comparable or better than standard drugs, from which 10 reports active compounds with MIC
lower than 5 μg mL-1.

Conclusion:
The findings of this work support the importance of pyrazole moiety in the structure of
antimicrobial compounds and the versatility of synthetic methodologies to obtain the target products.
Results clearly indicate that they are attractive target compounds for new antimicrobial drugs development.
We hope that this information will guide further studies on continuing the search for more effective,
highly active antimicrobial agents.