Ultrasound-assisted one-pot synthesis of tetrazolo[1,5-a]pyrimidines and their pharmacological evaluations

Abstract

A series of twelve tetrazolo[1,5-a]pyrimidine derivatives 4(a–l) were synthesized via an efficient, ultrasound-assisted one-pot multicomponent reaction of 5-aminotetrazole, malononitrile or acetylacetone, and various heterocyclic aromatic aldehydes in acetic acid under ultrasonic conditions. The optimized protocol afforded isolated yields of 85–93% within 12–15 minutes, offering significant advantages over existing methods, including milder conditions, reduced reaction times, and straightforward product isolation without intermediate purification. The synthesized derivatives were evaluated for antimicrobial activity against two Gram-positive bacteria (Staphylococcus aureus and Bacillus subtilis), two Gram-negative bacteria (Escherichia coli and Klebsiella pneumoniae), and one pathogenic fungus (Candida albicans) using the agar well diffusion method. Compounds 4g and 4l demonstrated near-equivalent activity to the aminoglycoside reference gentamicin against S. aureus, while compounds 4f, 4g, and 4l exceeded the antifungal reference nystatin against C. albicans. The anticancer activity assessed by MTT assay against the HeLa (cervical carcinoma) and HCT-116 (colorectal carcinoma) cell lines revealed that compound 4l (IC₅₀ = 13.4 ± 0.7 µM, HeLa; 22.6 ± 1.1 µM, HCT-116) and compound 4g outperformed the quercetin reference standard. Structure–activity relationship analysis identified the C-5 acetyl group and benzo[d][1,3]dioxol or 5-bromothiophene substituents at C-4 as key contributors to biological potency, establishing 4l and 4g as primary lead compounds for further studies.