2,4-Diaminothieno[2,3-d]pyrimidine analogs of trimetrexate and piritrexim as potential inhibitors of Pneumocystis carinii and Toxoplasma gondii dihydrofolate reductase

Abstract

A series of eight previously undescribed 2,4-diaminothieno[2,3-d]pyrimidine analogues of the potent dihydrofolate reductase (DHFR) inhibitors trimetrexate (TMQ) and piritrexim (PTX) were synthesized as potential drugs against Pneumocystis carinii and Toxoplasma gondii, which are major causes of severe opportunistic infections in AIDS patients. 2,4-Diamino-5-methyl-6-(aryl/aralkyl)thieno[2,3-d]pyrimidines with 3,4,5-trimethoxy or 2,5-dimethoxy substitution in the aryl/aralkyl moiety and 2,4-diamino-5-(aryl/aralkyl)thieno[2,3-d]pyrimidines with 2,5-dimethoxy substitution in the aryl/aralkyl moiety were obtained by reaction of the corresponding 2-amino-3-cyanothiophenes with chloroformamidine hydrochloride. The aryl group in the 5,6-disubstituted analogues was either attached directly to the hetero ring or was separated from it by one or two carbons, whereas the aryl group in the 5-monosubstituted analogues was separated from the hetero ring by two or three carbons. 2-Amino-3-cyano-5-methyl-6-(aryl/alkyl)thiophene intermediates for the preparation of the 5,6-disubstituted analogues were prepared from omega-aryl-2-alkylidene-malononitriles and sulfur in the presence of a secondary amine, and 2-amino-3-cyano-4-(aryl/aralkyl)thiophene intermediates for the preparation of the 5-monosubstituted analogues were obtained from omega-aryl-1-chloro-2-alkylidenemalononitriles and sodium hydrosulfide. Synthetic routes to the heretofore unknown ylidenemalononitriles, and the ketone precursors thereof, were developed. The final products were tested in vitro as inhibitors of DHFR from Pneumocystis carinii, Toxoplasma gondii, rat liver, beef liver, and Lactobacillus casei. A selected number of previously known 2,4-diaminothieno[2,3-d]pyrimidines lacking the 3,4,5-trimethoxyphenyl and 2,5-dimethoxyphenyl substitution pattern of TMQ and PTX, respectively, were also tested for comparison. None of the compounds was as potent as TMQ or PTX, and while some of them showed some selectivity in their binding to Pneumocystis carinii and Toxoplasma gondii versus rat liver DHFR, this effect was not deemed large enough to warrant further preclinical evaluation.

Structure-activity and structure-selectivity studies on diaminoquinazolines and other inhibitors of Pneumocystis carinii and Toxoplasma gondii dihydrofolate reductase

“…Our results suggest that a consequence of decreased affinity for the rat liver enzyme may be an increase in species selectivity. We have previously observed this tendency in another series of inhibitors (38).…”

“…Several 2,4-diamino-5-benzylpyrimidine derivatives related to trimethoprim but with a pyrrole substituent in the phenyl ring have recently been found to have selectivity ratios of Ͼ100 for P. carinii DHFR (31,45). A number of inhibitors of the 2,4-diaminopteridine (30), 2,4-diaminopyrido[2,3-d]pyridine (13), and 2,4-diaminothieno [2,3-d]pyrimidine (38) type have also recently been identified as being Ͼ10-fold selective for P. carinii DHFR in some instances and T. gondii DHFR in others. One of these, 2,4-diamino-6-phenylthiomethylpteridine, displayed a remarkable 320-fold selectivity for the T. gondii enzyme (30).…”

Efficacies of Lipophilic Inhibitors of Dihydrofolate Reductase against Parasitic Protozoa

“…The 2,4-diaminoquinazolines with an aromatic substituent at the position 5 were obtained from 2,4-diamino-5-iodoquinazoline and an arylalkene or arylalkyne via a palladium-catalyzed coupling reaction followed by catalytic hydrogenation (entries 43 to 45), by reductive coupling of 2,4-diaminoquinazoline-5-carbonitrile with an arylamine (entries 46 and 47), or by N methylation of a preformed 5-anilinomethylquinazoline (entries 48 and 49) (35). The 5-and 6-substituted 2,4-diaminothieno [2,3-d]pyrimidines (entries 50 to 54) were made from the corresponding 2-aminothiophene-3-carbonitriles and chloroformamidine hydrochoride (33,36), whereas the 2,4-diamino-6-anilinomethylthieno [2,3-d]pyrimidines (entries 55 to 58) were made via a four-step sequence from 2,4-diamino-5-methylthieno [2,3-d]pyrimidine (41). One member of the latter group (entry 58) was obtained by reductive dehalogenation of the corresponding 6-bromo compound (41).…”

Gewald reaction: synthesis, properties and applications of substituted 2-aminothiophenes

“…119 Thieno[2, 3-d]pyrimidine derivatives show pronounced antiinflammatory 120 , anti-tumor 121 , radioprotective and anti-convulsing activity. 122 The pharmacological versatility of the above system also present in substances with depressant or sedative properties 123 and compounds used for therapy of malaria 124 , tuberculosis 125 , Parkinson´s disease 126 and other diseases were designed.…”

“…Because the structure-based drug design program through substituted 2-aminothiophenes has been investigated broadly, up to this date there are many other research works dealing with the synthesis, pharmacology and application of thiophene-based structures in medicinal chemistry. 7,[12][13][14]36,37,51,69,100,101,[119][120][121][122][123][124][125][126][127] It is no doubt, that this area of Gewald-like thiophene derivatives exhibits the highest progress in a scope and utilization.…”