This study involves a comparative antidiabetic evaluation, antioxidant and anti-tubercular evaluation of quinoline-pyrazopyrimidines and their simple quinoline-4-arylamine analogues. The incorporation of pyrazopyrimidine ring to quinoline generally lowers the antidiabetic, antioxidant and antitubercular activity. The molecular docking simulations further discloses these compounds to be the allosteric inhibitors of the α-glucosidase.

Abstract

Two libraries of quinoline-based hybrids 1-(7-chloroquinolin-4-yl)-1H-pyrazolo[3,4–d]pyrimidin-4-amine and 7-chloro-N-phenylquinolin-4-amine were synthesized and evaluated for their α-glucosidase inhibitory and antioxidant properties. Compounds with 4-methylpiperidine and para-trifluoromethoxy groups, respectively, showed the most promising α-glucosidase inhibition activity with IC₅₀=46.70 and 40.84 μM, compared to the reference inhibitor, acarbose (IC₅₀=51.73 μM). Structure-activity relationship analysis suggested that the cyclic secondary amine pendants and para-phenyl substituents account for the variable enzyme inhibition. Antioxidant profiling further revealed that compounds with an N-methylpiperazine and N-ethylpiperazine ring, respectively, have good DPPH scavenging abilities with IC₅₀=0.18, 0.58 and 0.93 mM, as compared to ascorbic acid (IC₅₀=0.05 mM), while the best DPPH scavenger is NO₂-substituted compound (IC₅₀=0.08 mM). Also, compound with N-(2-hydroxyethyl)piperazine moiety emerged as the best NO radical scavenger with IC₅₀=0.28 mM. Molecular docking studies showed that the present compounds are orthosteric inhibitors with their quinoline, pyrimidine, and 4-amino units as crucial pharmacophores furnishing α-glucosidase binding at the catalytic site. Taken together, these compounds exhibit dual potentials; i. e., potent α-glucosidase inhibitors and excellent free radical scavengers. Hence, they may serve as structural templates in the search for agents to manage Type 2 diabetes mellitus. Finally, in preliminary assays investigating the anti-tubercular potential of these compounds, two pyrazolopyrimidine series compounds and a 7-chloro-N-phenylquinolin-4-amine hybrid showed sub-10 μM whole-cell activities against Mycobacterium tuberculosis.