Synthesis and Anti-Toxoplasma Activity of Novel Tetrahydropyrido[4,3-d]pyrimidine Derivatives

To develop highly effective and highly selective anti-Toxoplasma drugs, twenty novel tetrahydropyridines [4,3-d]pyrimidine derivatives were designed and synthesized via the principle of pharmacochemical molecular combination. Ethyl 1-benzyl-4-oxo-3-piperidinecarboxylate hydrochloride as starting material, the target compounds 7a-7t were obtained by seven step reaction. All target compounds were characterized via nuclear magnetic resonance spectroscopy(1H NMR, 13C NMR), mass spectrometry and elemental analysis. Methyl thiazolyl tetrazolium(MTT) method was used to investigate the anti-Toxoplasm activity in vitro, and the compound with the best activity was selected to further quantify the inhibitory activity against Toxoplasm dihydrofolate reductase(TgDHFR). The results showed that ten compounds had higher anti-Toxoplasma activity compared with the positive control drugs pyrimethamine and sulfadiazine. Compound 7p exhibited the most potent antiToxoplasma activity and commendable selectivity between TgDHFR and human dihydrofolate reductase(hDHFR) with half maximal inhibitory concentration(IC50) value of 15 nmol/L against TgDHFR and 1460 nmol/L against hDHFR. Molecular docking experiments showed that compound 7p could be strongly bound to TgDHFR through five hydrogen bonds, which could be deeply studied to develop new anti-Toxoplasma drugs.