Structure-based design of selective inhibitors of dihydrofolate reductase: Synthesis and antiparasitic activity of 2,4-diaminopteridine analogues with a bridged diarylamine side chain

Andre Rosowsky, Vivian Cody, Nikolai Galitsky, Hongning Fu, Andrew T. Papoulis, Sherry F. Queener

50 Scopus citations


As part of a larger search for potent as well as selective inhibitors of dihydrofolate reductase (DHFR) enzymes from opportunistic pathogens found in patients with AIDS and other immune disorders, N-[(2,4-diaminopteridin-6- yl)methyl]dibenz[b,f]azepine (4a) and the corresponding dihydrodibenz[b,f]azepine, dihydroacridine, phenoxazine, phenothiazine, carbazole, and diphenylamine analogues were synthesized from 2,4-diamino-6- (bromomethyl)pteridine in 50-75% yield by reaction with the sodium salts of the amines in dry tetrahydrofuran at room temperature. The products were tested for the ability to inhibit DHFR from Pneumocystis carinii (pcDHFR), Toxoplasma gondii (tgDHFR), Mycobacterium avium (maDHFR), and rat liver (rlDHFR). The member of the series with the best combination of potency and species selectivity was 4a, with IC50 values against the four enzymes of 0.21, 0.043, 0.012, and 4.4μM, respectively. The dihydroacridine, phenothiazine, and carbazole analogues were also potent, but nonselective. Of the compounds tested, 4a was the only one to successfully combine the potency of trimetrexate with the selectivity of trimethoprim. Molecular docking simulations using published 3D structural coordinates for the crystalline ternary complexes of pcDHFR and hDHFR suggested a possible structural interpretation for the binding selectivity of 4a and the lack of selectivity of the other compounds. According to this model, 4a is selective because of a unique propensity of the seven-membered ring in the dibenz[b,f]azepine moiety to adopt a puckered orientation that allows it to fit more comfortably into the active site of the P. carinii enzyme than into the active site of the human enzyme. Compound 4a was also evaluated for the ability to be taken up into, and retard the growth of, P. carinii and T. gondii in culture. The IC50 of 4a against P. carinii trophozoites after 7 days of continuous drug treatment was 1.9μM as compared with previously observed IC50 values of >340μM for trimethoprim and 0.27 μM for trimetrexate. In an assay involving [3H]uracil incorporation into the nuclear DNA of T. gondii tachyzoites as the surrogate endpoint for growth, the IC50 of 4a after 5 h of drug exposure was 0.077 μM. The favorable combination of potency and enzyme selectivity shown by 4a suggests that this novel structure may be an interesting lead for structure-activity optimization.

Original languageEnglish (US)
Pages (from-to)4853-4860
Number of pages8
JournalJournal of Medicinal Chemistry
Issue number23
StatePublished - Dec 8 1999

ASJC Scopus subject areas

  • Molecular Medicine
  • Drug Discovery

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