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A series of novel Mannich bases were designed, synthesized, and screened for their antimicrobial activity. The target compounds were synthesized from 4-(3-chlorophenyl)-5-(3-fluorophenyl)-2,4-dihydro-3 H -1,2,4-triazole-3-thione and different piperazine derivatives. The structures of the products were confirmed by 1 H and 13 C NMR and elemental analysis. The activity of piperazine derivatives against bacteria (Gram-positive: Staphylococcus epidermidis , Staphylococcus aureus , Micrococcus luteus , Bacillus cereus , and Bacillus subtilis ; Gram-negative: Escherichia coli , Pseudomonas aeruginosa , Klebsiella pneumoniae , and Proteus mirabilis ) and yeasts ( Candida glabrata , Candida krusei , and Candida parapsilosis ) was determined by the minimum inhibitory concentration and minimum bactericidal concentration values. Significant activity was observed against Gram-positive bacteria, mainly staphylococci ( PG7 - PG8 ) and bacteria of the genes of Micrococcus and Bacillus ( PG1-3 ), as well as selected strains of Gram-negative bacteria, including bacteria of the Enterobacteriaceae family ( PG7 ), while all tested compounds showed high fungistatic activity against Candida spp. yeasts, especially C. parapsilosis , with MICs ranging from 0.49 µg/mL ( PG7 ) to 0.98 µg/mL ( PG8 ) and 62.5 µg/mL ( PG1-3 ). In conclusion, the results obtained confirm the multidirectional antimicrobial activity of the newly synthesized piperazine derivatives. Furthermore, in silico studies suggest that the tested compounds are likely to have good oral bioavailability. The results obtained will provide valuable data for further research into this interesting group of compounds. The library of compounds obtained is still the subject of pharmacological research aimed at finding new interesting biologically active compounds.

The series of novel Mannich bases were synthesized and evaluated for their in vitro antibacterial activity against Gram-positive and Gram-negative bacterial strains. The results showed that all compounds were less active than the drugs used as reference, but some of them had moderate potency against Staphylococcus epidermidis ATCC 12228 and Bacillus subtilis ATCC 6633. The presence of a phenyl ring in the position 4 of piperazine seems to be necessary for antibacterial activity in this class of compounds., (© 2019 Wiley-VHCA AG, Zurich, Switzerland.)