Structure-Based Design and Synthesis of Lipophilic 2,4-Diamino-6-Substituted Quinazolines and Their Evaluation as Inhibitors of Dihydrofolate Reductases and Potential Antitumor Agents

Abstract

The synthesis and biological activities of 14 6-substituted 2,4-diaminoquinazolines are reported. These compounds were designed to improve the cell penetration of a previously reported series of 2,4-diamino-6-substituted-pyrido[2,3-d]pyrimidines which had shown significant potency and remarkable selectivity for Toxoplasma gondii dihydrofolate reductase (DHFR), but had much lower inhibitory effects on the growth of T. gondii cells in culture. The target N9-H analogues were obtained via regiospecific reductive amination of the appropriate benzaldehydes with 2,4,6-triaminoquinazoline, which, in turn, was synthesized from 2,4-diamino-6-nitroquinazoline. The N9-CH3 analogues were synthesized via a regiospecific reductive methylation of the corresponding N9-H precursors. The compounds were evaluated as inhibitors of DHFR from human, Pneumocystis carinii, T. gondii, rat liver, Lactobacillus casei, and Escherichia coli, and selected analogues were evaluated as inhibitors of the growth of tumor cells in culture. These analogues displayed potent T. gondii DHFR inhibition as well as inhibition of the growth of T. gondii cells in culture. Further, selected analogues were potent inhibitors of the growth of tumor cells in culture in the in vitro screening program of the National Cancer Institute with GI50s in the nanomolar and subnanomolar range. Crystallographic data for the ternary complex of hDHFR-NADPH and 2,4-diamino-6-[N-(2', 5'-dimethoxybenzyl)-N-methylamino]pyrido[2,3-d]pyrimidine, 1c, reveal the first structural details for a reversed N9-C10 folate bridge geometry as well as the first conformational details of a hybrid piritrexim-trimetrexate analogue.

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“…The key interactions involved in binding are summarised in Table 13 with reference to ligand 1ohk and Table 12 shows the corresponding features present in each ligand [33][34][35][36][37]. The target pharmacophore consists of D1, A1, H1, and H2.…”

Lipophilic Antifolate Trimetrexate Is a Potent Inhibitor of Trypanosoma cruzi : Prospect for Chemotherapy of Chagas' Disease

“…On the other hand, nonclassical antifolates lack the glutamate side chain (and are hence called lipophilic antifolates). They enter the cell via passive diffusion and therefore can be effective against these organisms (15). Consistent with this notion, the lipophilic antifolate TMQ is a potent inhibitor of Toxoplasma gondii and P. carinii (1,2).…”

“…The DHFR activity of the T. cruzi enzyme was measured in 50 mM Tris HCl buffer, pH 7.0, and that of the human enzyme was measured in 50 mM KH 2 PO 4 , 250 mM KCl, 5 mM ␤-mercaptoethanol (␤-ME), pH 7.3, under optimum conditions for each enzyme. The inhibitory activity of TMQ was determined by measuring reaction velocities at several fixed concentrations (5,10,15,20,25, and 30 M) of DHF and various concentrations (0, 6.55, 13.11, 19.66, and 26.22 nM) of TMQ. The concentration of NADPH was kept at 150 M. The reaction was initiated by adding 1 g of purified TcDHFR-TS or 3 g of hDHFR.…”

Design, synthesis and biological evaluation of novel quinazoline derivatives as potential anti-cancer agents

“…Numerous quinazoline derivatives have been reported to have anti-cancer activity [4][5][6] . In that context, these agents have shown inhibitory activity against thymidylate synthase [5][6][7] , dihydrofolate reductase and various receptor tyrosine kinases [8][9][10] .…”

“…In that context, these agents have shown inhibitory activity against thymidylate synthase [5][6][7] , dihydrofolate reductase and various receptor tyrosine kinases [8][9][10] . Dasatinib, the standard used in this study, is a multi-targeted kinase inhibitor 11 .…”