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Bioorganic & Medicinal Chemistry Letters Aug 2019Pneumocystis pneumonia (PCP) caused by Pneumocystis jirovecii (pj) can lead to serious health consequences in patients with an immunocompromised system. Trimethoprim...
Pneumocystis pneumonia (PCP) caused by Pneumocystis jirovecii (pj) can lead to serious health consequences in patients with an immunocompromised system. Trimethoprim (TMP), used as first-line therapy in combination with sulfamethoxazole, is a selective but only moderately potent pj dihydrofolate reductase (pjDHFR) inhibitor, whereas non-clinical pjDHFR inhibitors, such as, piritrexim and trimetrexate are potent but non-selective pjDHFR inhibitors. To meet the clinical needs for a potent and selective pjDHFR inhibitor for PCP treatment, fourteen 6-substituted pyrido[3,2-d]pyrimidines were developed. Comparison of the amino acid residues in the active site of pjDHFR and human DHFR (hDHFR) revealed prominent amino acid differences which could be exploited to structurally design potent and selective pjDHFR inhibitors. Molecular modeling followed by enzyme assays of the compounds revealed 15 as the best compound of the series with an IC of 80 nM and 28-fold selectivity for inhibiting pjDHFR over hDHFR. Compound 15 serves as the lead analog for further structural variations to afford more potent and selective pjDHFR inhibitors.
Topics: Folic Acid Antagonists; Humans; Models, Molecular; Pneumocystis; Pneumocystis carinii; Pyrimidines; Structure-Activity Relationship; Trimethoprim
PubMed: 31176699
DOI: 10.1016/j.bmcl.2019.06.004 -
Bioorganic & Medicinal Chemistry May 2018To combine the potency of trimetrexate (TMQ) or piritrexim (PTX) with the species selectivity of trimethoprim (TMP), target based design was carried out with the X-ray...
Targeting species specific amino acid residues: Design, synthesis and biological evaluation of 6-substituted pyrrolo[2,3-d]pyrimidines as dihydrofolate reductase inhibitors and potential anti-opportunistic infection agents.
To combine the potency of trimetrexate (TMQ) or piritrexim (PTX) with the species selectivity of trimethoprim (TMP), target based design was carried out with the X-ray crystal structure of human dihydrofolate reductase (hDHFR) and the homology model of Pneumocystis jirovecii DHFR (pjDHFR). Using variation of amino acids such as Met33/Phe31 (in pjDHFR/hDHFR) that affect the binding of inhibitors due to their distinct positive or negative steric effect at the active binding site of the inhibitor, we designed a series of substituted-pyrrolo[2,3-d]pyrimidines. The best analogs displayed better potency (IC) than PTX and high selectivity for pjDHFR versus hDHFR, with 4 exhibiting a selectivity for pjDHFR of 24-fold.
Topics: Amino Acids; Anti-Bacterial Agents; Catalytic Domain; Crystallography, X-Ray; Drug Design; Enzyme Assays; Folic Acid Antagonists; Humans; Hydrogen Bonding; Hydrophobic and Hydrophilic Interactions; Molecular Docking Simulation; Molecular Structure; Pneumocystis carinii; Protein Binding; Pyrimidines; Pyrroles; Sequence Homology, Amino Acid; Species Specificity; Tetrahydrofolate Dehydrogenase
PubMed: 29691153
DOI: 10.1016/j.bmc.2018.04.032 -
Acta Crystallographica. Section F,... Jun 2015To further define the interactions that enhance the selectivity of binding and to directly compare the binding of the most potent analogue...
To further define the interactions that enhance the selectivity of binding and to directly compare the binding of the most potent analogue {N(6)-methyl-N(6)-(3,4,5-trifluorophenyl)pyrido[2,3-d]pyrimidine-2,4,6-triamine; compound 26} in the series of bicyclic pyrido[2,3-d]pyrimidine analogues of piritrexim (PTX) with native human (h), Pneumocystis carinii (pc) and Pneumocystis jirovecii (pj) dihydrofolate reductase (DHFR) enzymes, the crystal structures of hDHFR complexed with N(6)-methyl-N(6)-(4-isopropylphenyl)pyrido[2,3-d]pyrimidine-2,4,6-triamine (compound 22), of hDHFR complexed with compound 26 and of pcDHFR complexed with N(6)-methyl-N(6)-1-naphthylpyrido[2,3-d]pyrimidine-2,4,6-triamine (compound 24) are reported as ternary complexes with NADPH. This series of bicyclic pyrido[2,3-d]pyrimidines were designed in which there was a transposition of the 5-methyl group of PTX to the N9 position of the pyrido[2,3-d]pyrimidine. It was hypothesized that the N9-methyl group would preferentially interact with Ile123 of pcDHFR (and Ile123 of pjDHFR), but not with the shorter Val115 in hDHFR. Structure-activity data for this series of antifolates revealed that a trifluoro derivative (26) was the most selective against pjDHFR compared with mammalian DHFR (h/pj = 35.7). Structural data for the hDHFR-26 complex revealed that 26 binds in a different conformation from that observed in the pcDHFR-26 complex. In the hDHFR-26 complex the trifluorophenyl ring of 26 occupies a position near the cofactor-binding site, with close intermolecular contacts with Asp21, Ser59 and Ile60, whereas this ring in the pcDHFR-26 complex is positioned away from the cofactor site and near Ile65, with weaker contacts with Ile65, Phe69 and Ile123. Comparison of the intermolecular contacts between the N9-methyl group with Val115/Ile123 validates the hypothesis that the N9-methyl substituent preferentially interacts with Ile123 compared with Val115 of hDHFR, as the weaker contact with Val115 in the hDHFR structure is consistent with its weaker binding affinity compared with pcDHFR. The results for the structures of hDHFR-22 and pcDHFR-24 show that their inhibitor-binding orientation is similar to that observed in pcDHFR-26 and the pcDHFR variant (F69N) reported previously. The naphthyl moiety of 24 makes several intermolecular contacts with the active-site residues in pcDHFR that help to stabilize the binding, resulting in a more potent inhibitor.
Topics: Amino Acid Motifs; Anti-Bacterial Agents; Catalytic Domain; Crystallization; Crystallography, X-Ray; Folic Acid Antagonists; Halogenation; Humans; Models, Molecular; Molecular Sequence Data; NADP; Pneumocystis carinii; Protein Binding; Pyrimidines; Recombinant Proteins; Species Specificity; Structure-Activity Relationship; Tetrahydrofolate Dehydrogenase
PubMed: 26057816
DOI: 10.1107/S2053230X15008468