Synthesis of 2-aminopyridopyrimidinones and their plasmepsin I, II, IV inhibition potency

Malarial aspartic protease, plasmepsin (Plm), is perspective antimalarial drug target. Following up our previosly identified 2-aminoquinazolin-4(3H)-one-based inhibitors, 2-aminopyrido[2,3-d]-, -[3,2-d]-, and -[4,3-d]pyrimidin-4(3H)-ones bearing subpocket-specific substituents at position 7 were prepared and tested for their Plm I, II, IV inhibition potency. The position of the nitrogen atom in 2-aminopyridopyrimidinones plays significant role in the inhibitory potency against Plms. Pyrido[2,3-d]pyrimidin-4(3H)-one derivatives showed poor inhibitory potency against Plms I, II, IV irrespectively of the substituent at position 7. However, pyrido[4,3-d]pyrimidin-4(3H)-ones and pyrido[3,2-d]pyrimidin-4(3H)-ones were more appropriate scaffolds for Plm inhibitor development. Particularly, 2-amino-7-[4-(3-phenylpropyl)phenyl]-3-[(tetrahydrofuran-2-yl)methyl]pyrido[3,2-d]pyrimidin-4(3H)-one showed very high potency against Plm IV subtype and high selectivity against human aspartic protease, cathepsin D.