SAR refinement of antileishmanial N(2),N(4)-disubstituted quinazoline-2,4-diamines

Visceral leishmaniasis is a neglected parasitic disease that has a high fatality rate in the absence of treatment. New drugs that are inexpensive, orally active, and effective could be useful tools in the fight against this disease. We previously showed that N(2),N(4)-disubstituted quinazoline-2,4-diamines displayed low- to sub-micromolar potency against intracellular Leishmania, and lead compound N(4)-(furan-2-ylmethyl)-N(2)-isopropyl-7-methylquinazoline-2,4-diamine (4) exhibited modest efficacy in an acute murine model of visceral leishmaniasis. In the present work, thirty-one N(2),N(4)-disubstituted quinazoline-2,4-diamines that had not previously been examined for their antileishmanial activity were evaluated for their potency and selectivity against Leishmania donovani, the causative parasite of visceral leishmaniasis. Quinazoline-2,4-diamines with aromatic substituents at both N(2) and N(4) exhibited potent in vitro antileishmanial activity but relatively low selectivity, while compounds substituted with small alkyl groups at either N(2) or N(4) generally showed lower antileishmanial potency but were less toxic to a murine macrophage cell line. Based on their in vitro antileishmanial potency, N(4)-benzyl-N(2)-(4-chlorobenzyl)quinazoline-2,4-diamine (15) and N(2)-benzyl-N(4)-isopropylquinazoline-2,4-diamine (40) were selected for in vivo evaluation of their pharmacokinetic and antileishmanial properties. While 15 displayed a longer plasma half-life and a greater area under the curve than 40, both compounds showed low efficacy in an acute murine visceral leishmaniasis model. Although the present study did not identify new quinazoline-2,4-diamines with promising in vivo efficacy, the reduced in vitro toxicity of derivatives bearing small alkyl groups at either N(2) or N(4) may provide clues for the design of safe and effective antileishmanial quinazolines.