Epi-croomine and croomine from Stemona tuberosa antimalarial drug for inhibiting dihydrofolate reductase (DHFR) activity and their molecular modeling

One of the mechanism actions of antimalarial drugsis by an inhibiting on the enzyme dihydrofolate reductase (DHFR), an enzyme target antifolate drug. Epi-croomine and croomine, are alkaloids isolated from Stemonatuberosa showed DHFR inhibition with K_i of 61.14 and 100.59 μM and K_M values of30.68 and 27.06 μM at 10 ppm. The IC₅₀ to the DHFR of croomine and pyrimethamine were 5.29 and 7.71 μM, respectively. Tuberostemonine is not active to the enzyme. The kinetic analysis showed that both epi-croomine and croomine competitively inhibited to the human DHFR recombinant. The molecular modeling of the compounds to the human DHFR was estimate depi-croomine and croomine’s binding free energy of -6.66 and -7.60 kcal/mol. The docking showed that both epi-croomine and croomine could possibly form hydrogen bonds with the amino acid residue of theAla9, which residues on the active site of the enzyme.