Characterizing the Antimicrobial Activity of N2,N4-Disubstituted Quinazoline-2,4-Diamines toward Multidrug-Resistant Acinetobacter baumannii.

We previously reported a series of N2,N4-disubstituted quinazoline-2,4-diamines as dihydrofolate reductase inhibitors with potent in vitro and in vivo antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) strains. In this work, we extended our previous study to the Gram-negative pathogen Acinetobacter baumannii We determined that optimized N2,N4-disubstituted quinazoline-2,4-diamines are strongly antibacterial against multidrug-resistant A. baumannii strains when the 6-position is replaced with a halide or an alkyl substituent. Such agents display potent antibacterial activity, with MICs as low as 0.5 µM, while proving to be strongly bactericidal. Interestingly, these compounds also possess the potential for antibiofilm activity, eradicating 90% of cells within a biofilm at or near MICs. Using serial passage assays, we observed a limited capacity for the development of resistance toward these molecules (4-fold increase in MIC) compared to existing folic acid synthesis inhibitors, such as trimethoprim (64-fold increase) and sulfamethoxazole (128-fold increase). We also identified limited toxicity toward human cells, with 50% lethal doses (LD50s) of ≤23 µM for lead agents 4 and 5. Finally, we demonstrated that our lead agents have excellent in vivo efficacy, with lead agent 5 proving more efficacious than tigecycline in a murine model of A. baumannii infection (90% survival versus 66%), despite being used at a lower dose (2 versus 30 mg kg-1). Together, our results demonstrate that N2,N4-disubstituted quinazoline-2,4-diamines have strong antimicrobial and antibiofilm activities against both Gram-positive organisms and Gram-negative pathogens, suggesting strong potential for their development as antibacterial agents.

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.