Our earlier studies showed that the thione tautomer is energetically favored (Wujec
et al., 2007). The IR spectra of compounds 7–9 showed the absorption bands at 3,437–3,411 cm−1 and 1,331–1,328 cm−1, indicating the presence of NH and C=S groups, respectively. In the 1H-NMR spectra, NH proton resonated as a singlet at ~14 ppm. Crystallographic data (unpublished results) also confirm the existence of the mentioned compounds as the C=S tautomers. Scheme 1 Synthetic route to target compounds 10–21. Reagents and conditions: a EtOH, reflux, 5 min; b 2 % Selleckchem VX809 NaOH, reflux, 2 h; c HCHO, amine, EtOH, 30 min The Mannich reaction was carried out in mild conditions; it was quick (30 min) and efficient (yields: 76–87 %). The structure and purity of the products (10–21) was confirmed using 1H-NMR, 13C-NMR (for selleck kinase inhibitor compound 20), and IR spectra as well as elemental analysis. The 1H-NMR spectra showed characteristic signals which indicated the presence of aminomethyl fragment. Two protons of the N2–CH2– group resonated as a singlet in the range of 5.22–5.34 ppm, while the signals
of the amine residues were visible at 1.20–3.76 ppm. In addition this website to this, peaks characteristic for para-substituted phenyl rings were visible in the area typical for aromatic protons. The IR spectra also confirmed the suggested structure of the Mannich bases (10–21). Antibacterial screening The antibacterial activity of compounds 10–21 was determined for Gram-positive and Gram-negative bacteria. The growth of Gram-negative bacteria (Escherichia coli ATCC 25922, Klebsiella pneumoniae ATCC 13883, Proteus mirabilis ATCC 12453, and Pseudomonas aeruginosa ATCC 9027) was not inhibited by any of the compounds. Therefore, Table 1 shows the Mannich bases activity only for five investigated Gram-positive bacterial strains. The activity toward the pathogenic Staphylococcus aureus strains was moderate. Minimum concentrations which inhibited the growth of S. aureus ATCC 25923 ranged to 31.25 μg ml−1 (15, 18, 19), and the most active toward
C-X-C chemokine receptor type 7 (CXCR-7) methicillin-resistant (MRSA) strain were derivatives with diethylaminomethyl (18) and pyrrolidinylmethyl (19) substituents. In both cases, the MIC values equaled 62.5 μg ml−1. Opportunistic (relatively pathogenic) bacteria was by far more sensitive to the newly obtained compounds. In the case of Bacillus cereus ATCC 10876, the activity of three derivatives (14, 15, 21) was similar to the activity of ampicillin, and the activity of another two derivatives (18, 19) was twice as strong. Moreover, the antibacterial activity of the compound with the N2-pyrrolidinylmethyl fragment (15) toward Bacillus subtilis ATCC 6633 was as strong as cefuroxime’s; as far as Micrococcus luteus ATCC 10240 is concerned, the most active compound was the derivative of 4-(4-bromophenyl)-5-(4-chlorophenyl)-2,4-dihydro-3H-1,2,4-triazole-3-thione with pyrrolidinylmethyl substituent (19, MIC = 7.81 μg ml−1).