New thiazolyl-pyrazoline derivatives bearing nitrogen mustard as potential antimicrobial and antiprotozoal agents

A new series of N-substituted pyrazoline derivatives 6a-g, 7a-g, 8a-g, and 9a-g was synthetized by reaction of hydrazine derivatives and chalcone-thiazole hybrids bearing nitrogen mustard 5a-g. The chalcones 5a-g were obtained by Claisen-Schmidt condensation of thiazole-2-nitrogen mustard 3 and selected acetophenones 4a-g. These new compounds 6/7/8/9a-g were screened for their antifungal activity against Cryptococcus neoformans, with IC₅₀ values of 3.9-7.8 µg/ml for the N-3,5-dichlorophenyl pyrazolines 9e-g. Interestingly, those compounds show low cytotoxic effects toward erythrocytes (RBC). In addition, N-acetyl (6a,b) and N-formyl pyrazolines (7a, 7b, 7c, and 7g) showed inhibitory activity against methicillin-susceptible Staphylococcus aureus, methicillin-resistant S. aureus, and vancomycin-intermediate S. aureus, with the most important minimum inhibitory concentration values ranging from 31.25 to 125 µg/ml. Regarding the antiprotozoal activity, thiazolyl-pyrazolines 9g, 8f, and 7c display high activity against Plasmodium falciparum, Leishmania (V) panamensis, and Trypanosoma cruzi, with EC₅₀ values of 11.80, 6.46, and 4.98 μM, respectively, and with 7c being approximately 2.6-fold more potent than benznidazole with a selectivity index of 1.61 on U-937 human cells, showing promising potential as a novel antitrypanosomal agent.