Discovery of 5-Phenylpyrazolopyrimidinone Analogs as Potent Antitrypanosomal Agents with In Vivo Efficacy

Abstract

Human African Trypanosomiasis (HAT), caused by Trypanosoma brucei, is one of the neglected tropical diseases with a continuing need for new medication. We here describe the discovery of 5-phenylpyrazolopyrimidinone analogs as a novel series of phenotypic antitrypanosomal agents. The most potent compound, 30 (NPD-2975), has an in vitro IC50 of 70 nM against T. b. brucei with no apparent toxicity against human MRC-5 lung fibroblasts. Showing good physicochemical properties, low toxicity potential, acceptable metabolic stability, and other pharmacokinetic features, 30 was further evaluated in an acute mouse model of T. b. brucei infection. After oral dosing at 50 mg/kg twice per day for five consecutive days, all infected mice were cured. Given its good drug-like properties and high in vivo antitrypanosomal potential, the 5-phenylpyrazolopyrimidinone analog 30 represents a promising lead for future drug development to treat HAT.

Identification of potent and orally efficacious phosphodiesterase inhibitors in sCryptosporidium parvum-infected immunocompromised mice

“…Despite the critical role of phosphodiesterases in controlling levels of cellular cAMP and cGMP and their proven druggability, there is limited precedence for targeting parasite phosphodiesterases for drug development. Trypanosoma brucei PDEB1 is a chemically validated therapeutic target for Human African Trypanosomiasis (HAT) for which the most advanced compounds are curative in a mouse model [52][53][54][55][56] . Benzoxaborole and other inhibitors of Schistosoma mansoni PDE4A (the enzyme used here to incorporate metal ions into the CpPDE1 and CpPDE2 AlphaFold models) have been identified 57,58 , but the best compounds only modestly reduce worm burden in S. mansoni infected mice, raising questions about suitability of the target 59,60 .…”

Lead Optimization of the 5-Phenylpyrazolopyrimidinone NPD-2975 toward Compounds with Improved Antitrypanosomal Efficacy

“…A promising "hit" series has already been reported as a result of the phenotypic screening approach, where the most potent compound NPD-2975 (2) showed an IC 50 of 70 nM against T. b. brucei with confirmed in vivo efficacy. 21 Despite high potency both in vitro and in vivo, one of the drawbacks was its moderate metabolic stability. Taking NPD-2975 (2) as a starting point, the present study reports our lead optimization efforts to further improve the antitrypanosomal efficacy and pharmacological/pharmacokinetic profile in the series of 5-phenylpyrazolopyrimidinones.…”

“…The ring-closure reaction of 34 was completed under the same basic conditions as described for the synthesis of 2. 21 In Vitro Evaluation against T. brucei. In our initial optimization of the 5-phenylpyrazolopyrimidinone 2 (NPD-2975) (Table 1), we investigated the effect of methylation on the three nitrogen atoms and replacement of the carbonyl group with an amino group.…”

“…A phenotypic screening strategy was employed for hit discovery next to a structure-based strategy focusing on parasite cyclic nucleotide phosphodiesterases (PDEs). A promising “hit” series has already been reported as a result of the phenotypic screening approach, where the most potent compound NPD-2975 ( 2 ) showed an IC 50 of 70 nM against T. b. brucei with confirmed in vivo efficacy . Despite high potency both in vitro and in vivo , one of the drawbacks was its moderate metabolic stability.…”

“…Next, the amidation and reduction reactions afforded the key intermediates 10 and 14 without purification of 9 and 13. The last ring-closure steps were completed with 4-fluorobenzoic acid as reported for 2 21. To improve solubility and structural diversity, an amino group was introduced with the route shown in Scheme 3.…”