Synthesis and Evaluation of Hydrazonomethyl-Quinolin-8-ol and Pyrazol-3-yl-Quinolin-8-ol Derivatives for Antimicrobial and Antimalarial Potential.

Background: Quinoline is a well-established nucleus displaying various biological activities. Quinolin-8-ol-containing compounds are reported for antimicrobial as well as antimalarial activity. Hydrazone- and pyrazole-containing compounds are also reported for antimicrobial activity. In this work, we have synthesized hydrazonomethyl-quinolin-8-ol and pyrazol-3-yl-quinolin-8-ol derivatives retaining quinolin-8-ol along with hydrazone/pyrazole pharmacophores.

Objective: The objective of this work was to synthesise and evaluate in vitro hydrazonomethylquinolin- 8-ol and pyrazol-3-yl-quinolin-8-ol derivatives for antifungal, antibacterial and antimalarial activity.

Methods: Designed and synthesized hydrazonomethyl-quinolin-8-ol and pyrazol-3-yl-quinolin-8- ol derivatives were evaluated for antifungal (against Candida albicans, Aspergillus fumigatus and Cryptococcus neoformans), antibacterial (against methicillin resistant Staphylococcus aureus (MRSA), Escherichia Coli, Pseudomonas aeruginosa and Klebsillae pneumoniae) as well as antimalarial (against Plasmodium falciparum D6 and W2 strains) activity.

Results: Hydrazonomethyl-quinolin-8-ol (15.1-15.28) and pyrazol-3-yl-quinolin-8-ol derivatives (16.1-16.21 and 20.1-20.18) were synthesized in good to moderate yield. One-pot synthesis of pyrazol- 3-yl-quinolin-8-ol derivatives (16.1-16.21 and 20.1-20.18) was achieved. Compounds 15.3, 15.6, 15.7, 15.9-15.14, 15.16-15.19, 15.22 and 15.24 were found more potent compared to reference standard fluconazole (IC = 3.20 μM) against C. albicans with IC value less than 3 μM. Compounds 15.1, 15.2, 15.21 and 15.23 showed almost similar activity to reference standard fluconazole against C. albicans. Compounds 15.1-15.3, 15.9-15.12, 15.14-15.17, and 15.21-15.23 also showed good activity against fluconazole-resistant strain A. fumigatus with IC50 value less than 3 μM. Compounds 15.2-15.4, 15.7, 15.9, 15.17, 15.20 showed good antimalarial activity against P. falciparum D6 as well as P. falciparum W2 with IC50 values of 1.84, 1.83, 1.56, 1.49, 1.45, 1.97, 1.68 μM and 1.86, 1.40, 1.19, 1.71, 1.16, 1.34, 1.61 μM, respectively. 5-Pyrazol-3-yl-quinolin-8-ol derivatives, such as 16.3, 16.5, 16.11, 16.13, 16.19, 16.20, also showed antimalarial activity against P. falciparum D6 and W2 strains with IC50 values of 2.23, 2.16, 2.99, 2.99, 2.73, 2.12 μM and 2.91, 3.60, 4.61, 2.71, 2.31, 2.66 μM, respectively.

Conclusion: Most of the 5-hydrazonomethyl-quinolin-8-ol derivatives showed good antifungal activity against C. albicans, A. fumigatus and C. neoformans. Most of the 5-hydrazonomethylquinolin- 8-ol derivatives were found more potent than reference standard fluconazole. These derivatives may be considered as leads for further development of antifungal agents.