Synthesis and Evaluation of Some New Pyridines as Possible P-gp Inhibitors with Reduced Calcium Channel Blocking Activity

The 1,4-dihydropyridine derivatives (DHPs) (3a-b and 4a-c) were oxidized with iodine in methanol to produce five new, hitherto unreported pyridine derivatives (5a-b and 6a-c). The “Everted sac method” was used to assess the DHPs and their pyridines for potential p-glycoprotein (P-gp) inhibitory or multidrug resistance reversal action. Domperidone, a P-gp substrate, was examined for intestinal absorption in everted rat jejunal segments in the presence and absence of DHPs (3a-b and 4a-c) and pyridines (5a-b and 6a-c) at doses of 30 μg/mL and 100 μg/mL. The standard was Verapamil, a known P-gp inhibitor (30 μg/mL and 100 μg/mL). The P-gp inhibition of all the tested compounds was higher than Verapamil. The P-gp inhibition of compounds 5b and 6b was the highest. Utilizing isolated rat ileum, the newly synthesized pyridine derivatives calcium channel blocking efficacy was also investigated. The strongest Ca2+ channel-blocking action was seen with compound 5b. It was determined to be equivalent to Nifedipine, the gold standard. Strong P-gp inhibitor compound 6b has little calcium channel-blocking action.