Novel analogues of pyrimethamine (Pyr) and cycloguanil (Cyc) have been synthesized and tested as inhibitors of Plasmodium falciparum dihydrofolate reductase carrying triple (N51I+ C59R+ S108N, C59R+ S108N+ I164L) and quadruple (N51I+ C59R+ S108N+ I164L) mutations responsible for antifolate resistance. The inhibitors were designed to avoid steric clash of the p-Cl group of the inhibitors with the side chain of Asn108, augmented by ...