New Route to the Synthesis of Novel Pyrazolo[1,5-a]pyrimidines and
Evaluation of their Antimicrobial Activity as RNA Polymerase Inhibitors
Authors: Abdallah Amira E. M. , Elgemeie Galal H. 
Published: March 2022

Aims:
The current study aimed to synthesize novel pyrazolo[1,5-a]pyrimidines based on 5-
aminopyrazoles 3, evaluate their antimicrobial activity, and study the minimum inhibitory concentration (MIC)
for the most active compounds. In addition, molecular docking studies and RNA polymerase inhibitory activity
were determined.

Background:
Starting with our previously reported 5-aminopyrazoles 3, a number of novel pyrazolo[1,5-
a]pyrimidines were synthesized. Due to the similarity of pyrazolopyrimidine derivatives with the purine systems,
pyrazolopyrimidines are important in many different biological applications, most notably as anti-tumor, antibacterial,
and hepatitis C virus inhibitors. The pharmaceutical applications of the pyrazolopyrimidine derivatives
were explained in several approved drugs like Indiplon, Zaloplan, and Ocinaplon.

Objective:
To prepare a novel antimicrobial agent, namely pyrazolo[1,5-a]pyrimidine, reveal their structures
using different spectral data, the minimum inhibitory concentration (MIC) for the most active compounds was
evaluated, and both the molecular docking and the RNA polymerase inhibitory activity were determined.

Methods:
A number of different pyrazolopyrimidines namely 2-(phenylamino)-6,11-dihydrobenzo[g]pyrazolo
[1,5-a]quinazoline-3-carboxamides (5a-c), (E)-5,7-dimethyl-2-(phenylamino)-6-(phenyldiazenyl)pyrazolo-[1,5-
a]pyrimidine-3-carboxamides (7a-c), 7-amino-2-(phenylamino) pyrazolo[1,5-a]pyrimidine-3-carboxamides (11af),
7-amino-2-(phenylamino)-5-(2-thienyl)pyrazolo[1,5-a]pyrimidine-3-carboxamides (14-f) and ethyl 7-amino-3-
carbamoyl-2-(phenylamino)-5-(4-pyridyl)pyrazolo[1,5-a]pyrimidine-6-carboxylate derivatives (14g-i) were synthesized
through the reaction of 5-aminopyrazoles 3 with a variety of chemical reagents. On the other hand, the
evaluation of the antimicrobial activity for all the prepared compounds was screened through different strains as
Gram-positive bacteria, such as staphylococcus aureus and Streptococcus mutans, and Gram-negative bacteria,
such as Escherichia coli, Pseudomonas aeruginosa, and klebsiella. The antifungal activity was determined by
Candids Albicans fungal strain, and the MIC of the most active compounds was measured. The molecular docking
was recorded, and the RNA polymerase inhibitory activity was estimated for the high docking score compounds.

Results:
Compounds 5a, 5b, 5c, 7a, 7b, 7c, 11d, 14b, and 14h were the most active compounds against some of
the bacterial and fungal tested strains. MIC was determined for the most active tested compounds. As an antimicrobial
agent, compound 7b was the most potent, with a high docking score and RNA polymerase inhibitory
activity (IC50= 0.213 μg/ml) compared to Rifampicin (IC50= 0.244 μg/ml). The reactivity of the latter compound
was attributed to the presence of 4-Br-C6H4 moiety. The results demonstrated that docking studies on the most
active compounds in the RNA polymerase active site were consistent with in vitro assays.

Conclusion:
The resultant novel bioactive pyrazolo[1,5-a]pyrimidine derivatives were synthesized based on 5-
aminopyrazole derivatives 3. The current study evaluated the antimicrobial activity for all the prepared compounds,
followed by the determination of the MIC for the most potent active compounds. The molecular docking
study was performed, and it was appropriate with the in vitro activity. The RNA polymerase inhibitory activity
was assessed for the most active antimicrobial compounds with a high docking score (7b, 7c, 14a, 14b, 14e, 14i).
Compound 7b was the most potent compound inhibiting RNA polymerase enzyme compared to the reference
drug Rifampicin.

Other:
The novel prepared heterocyclic systems are extremely important in a variety of domains, especially biological
and pharmacological ones.