To exploit the potential antimicrobial activities of azabicyclic skeleton based compounds, a set of 2r,4c-diaryl-3-azabicyclo[3.3.1]nonan-9-one-4-methyl-1,2,3-thiadazole-5-carbonyl hydrazones were synthesized. Unambiguous structural elucidation has been carried out by investigating IR, H(1), C(13) NMR, and elemental analysis. 2D NMR spectra ((1)H-(1)H COSY, HSQC, HMBC, and NOESY) were recorded for a representative compound, 12, to confirm the proposed structure for 9-15. Antimicrobial activity assessment of synthesized hydrazones 9-15 has been evaluated by screening against selective strains. Both bacteria and fungi of various forms along with standard drug have been taken for the analysis. Difference in the potency of activity against the strains has been evaluated on the basis of SAR, and it has been revealed that substitution of electron-withdrawing halogens (chloro, fluoro, and bromo) at para positions of the phenyl (10, 12, and 13) enhanced the antifungal and antibacterial activities against tested organisms compared to other hydrazone derivatives.

The structures of the newly synthesized 4-methyl-N′-(3-alkyl-2r,6c-diarylpiperidin-4-ylidene)-1,2,3-thiadiazole-5-carbohydrazide (5a–5l) were confirmed by spectral and elemental analysis. The difference in the potency of activity against various free radicals, human cancer cells and microbial strains has been evaluated by SAR. Compounds with electron-donating methoxy (5i and 5c) and methyl (5h and 5b) substitutions at the para position of the phenyl showed excellent free radical scavenging effects. In the tested compounds, electron withdrawing fluoro (5k and 5e), chloro (5j and 5d), and bromo (5l and 5f) substitution at the para position of the phenyl ring attached to C-2 and C-6 carbons of the piperidine moiety outperformed cytotoxic and antimicrobial activities. Our findings suggest that the antioxidant, anti-tumor and anti-microbial activities of compounds 5a–5l create promising leads for the development of potent anti-tumor and anti-microbial agents.

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