Microwave-Assisted Green Synthesis and Antimicrobial Evaluation of Triphenyl-[1,2,4]-triazolo-[1,5-a]pyrimidine Analogues

Abstract

A rapid, environmentally friendly and efficient microwave-assisted one-pot synthesis was developed for novel 2,5,7-triphenyl-1,2,4-triazolo[1,5-a]pyrimidine derivatives using a recyclable polyphosphoric acid-silica (PPA-SiO₂) catalyst. The compounds were synthesized via a three-component cyclocondensation of substituted benzaldehydes, acetophenone and 3-amino-5-phenyl-1,2,4-triazole under solvent-free microwave irradiation. Optimised conditions yielded products in 90-95% within 6-12 min, representing a significant improvement over the conventional method. The catalyst was easily recovered and reused without loss of activity, demonstrating its practical and sustainable utility. The synthesised derivatives were fully characterized by melting point determination, FT-IR, ¹H NMR, ¹³C NMR and high-resolution mass spectrometry (HRMS), confirming the formation of the triazolopyrimidine framework. The compounds were evaluated for their in vitro antimicrobial activity against representative Gram-positive bacteria (Staphylococcus aureus and Bacillus subtilis), Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa) and fungal strains (Candida albicans and Aspergillus niger) using the minimum inhibitory concentration (MIC) method. Several derivatives exhibited moderate to good antimicrobial activity, particularly those bearing electron-withdrawing substituents such as nitro, chloro and bromo groups, which showed lower MIC values than the unsubstituted analogue. The study demonstrates that microwave-assisted synthesis employing recyclable PPA-SiO₂ provides an efficient green synthetic strategy for preparing biologically active triazolopyrimidines with antimicrobial potential.