2,4-Diaminopyrido[3,2-d]pyrimidine inhibitors of dihydrofolate reductase from Pneumocystis carinii and Toxoplasma gondii.

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Rosowsky A, Forsch RA, Queener SF

2,4-Diaminopyrido[3,2-d]pyrimidine inhibitors of dihydrofolate reductase from Pneumocystis carinii and Toxoplasma gondii.

J Med Chem. 1995 Jul 7;38(14):2615-20.

PubMed ID
7629801 [ View in PubMed
]
Abstract

Six previously unknown 2,4-diamino-6-(anilinomethyl)- and 2,4-diamino-6-[(N-methylanilino)-methyl]pyrido[3,2-d]pyrimidines (5-10) were synthesized from 2,4-diamino-6-(bromomethyl)-pyrido[3,2-d]pyrimidine hydrobromide (11.HBr) by treatment with the appropriate aniline or N-methylaniline in dimethylformamide at room temperature, with or without NaHCO3 present. Compounds 5-10 were tested as inhibitors of dihydrofolate reductase from Pneumocystis carinii, Toxoplasma gondii, and rat liver as a part of a larger effort directed toward the discovery of lipophilic nonclassical antifolates combining high enzyme selectivity and high potency. Of the six analogues tested, the most potent and selective against T. gondii DHFR was 2,4-diamino-6-[(3',4',5'-trimethoxy-N-methylanilono)methyl]pyrido[ 3,2-d d pyrimidine (7), which had an IC50 of 0.0047 microM against this enzyme as compared with 0.026 microM against the rat liver enzyme. The potency of 7 against T. gondii DHFR was similar to that of trimetrexate (TMQ, 1) and piritrexim (PTX, 2) but was > 500-fold greater than that of trimethoprim (TMP, 3). However, while 7 was more selective than either TMQ (19x) or PTX (63x) against this enzyme, its selectivity in comparison with TMP was 8-fold lower. 2,4-Diamino-6-[3',4',5'-trimethoxyanilino)methyl]pyrido[3,2-d]pyri midin e (6) was 17-fold less active than 7 and was also less selective. 2,4-Diamino-6-[(3',4'-dichloro-N-methylanilino)methyl]pyrido[3, 2-d]pyrimidine (10) had an IC50 of 0.022 microM against P. carinii DHFR and was comparable in potency to TMQ and PTX. The species selectivity of 10 for P. carinii versus rat liver DHFR was greater than that of either TMQ (21-fold) or PTX (31-fold). On the other hand, even though 10 was slightly more active than TMQ against the P. carinii enzyme, its selectivity was 7-fold lower than that of TMP. Thus, the goal of combining high enzyme binding activity, which is characteristic of the fused-ring compounds TMQ and PTX, with high selectivity for T. gondii and P. carinii DHFR versus rat liver DHFR, which is characteristic of the monocyclic compound TMP, remained unmet in this limited series.

DrugBank Data that Cites this Article

Binding Properties
DrugTargetPropertyMeasurementpHTemperature (°C)
2,4-Diamino-5-Methyl-6-[(3,4,5-Trimethoxy-N-Methylanilino)Methyl]Pyrido[2,3-D]PyrimidineDihydrofolate reductaseIC 50 (nM)13N/AN/ADetails
2,4-Diamino-5-Methyl-6-[(3,4,5-Trimethoxy-N-Methylanilino)Methyl]Pyrido[2,3-D]PyrimidineDihydrofolate reductaseIC 50 (nM)0.85N/AN/ADetails
PiritreximDihydrofolate reductaseIC 50 (nM)31N/AN/ADetails
PiritreximDihydrofolate reductaseIC 50 (nM)17N/AN/ADetails
TrimethoprimDihydrofolate reductaseIC 50 (nM)2700N/AN/ADetails
TrimethoprimDihydrofolate reductaseIC 50 (nM)12000N/AN/ADetails
TrimetrexateDihydrofolate reductaseIC 50 (nM)42N/AN/ADetails
TrimetrexateDihydrofolate reductaseIC 50 (nM)10N/AN/ADetails