Purpose: To prepare and evaluate some quinoline-pyrazoline-based naphthalenyl thiazole derivatives
as antimicrobial agents.
Methods: Some quinoline-pyrazoline-based naphthalenyl thiazoles (
5a-5e and
6a-6e) were prepared
by reacting 5-(2-chloroquinolin-3-yl)-3-substitutedphenyl-4,5-dihydro-1H-pyrazole-1-carbothiamides (4a-4e) with 2-bromo-1-(1-naphthyl)ethanone and 2-bromo-1-(2-naphthyl)ethanone, respectively. Fourier
transform infra-red (FTIR),
13C-Nuclear magnetic resonance (
13C-NMR),
1H-Nuclear magnetic
resonance (
1H-NMR), elemental analysis, and mass spectrometry were used to elucidate and confirm
the chemical structures of the target compounds. Serial plate dilution technique was used to evaluate
the antimicrobial activity of the title compounds using ketoconazole and ofloxacin as standards, and
their minimum inhibitory concentrations (MIC) were determined.
Results: A total of ten compounds, (
5a-5e) & (
6a-6e) were prepared. Compound
6d (R = 4-F,
naphthalen-2-yl derivative) exhibited antimicrobial activities that were higher than those of the standard
drug (ofloxacin) against
S. aureus
(MIC = 25 μg/mL, p < 0.05),
S. epidermidis
(MIC = 25 μg/mL, p <
0.0001), K. pneumonia (MIC = 25 μg/mL, p < 0.0001), P. vulgaris (MIC = 25 μg/mL, p < 0.0001) and P.
citrinum (MIC = 25 μg/mL, p < 0.0001). Compound
5d (R = 4-F, naphthalen-1-yl derivative) displayed
higher antifungal activity than ketoconazole against
C. albicans
(MIC = 25 μg/mL, p <0.0001).
Conclusion: The naphthalen-2-yl derivatives (
6a-6e) are superior antimicrobial agents as compared to
the naphthalen-1-yl derivatives (
5a-5e) and the presence of 4-F substituent in 6d and 5d is essential for
stronger antimicrobial activity. The compound
6d needs further investigations related to its safety and
efficacy.
