Catechol Pyrazolinones as Trypanocidals: Fragment-Based Design, Synthesis, and Pharmacological Evaluation of Nanomolar Inhibitors of Trypanosomal Phosphodiesterase B1

Abstract

Trypanosomal phosphodiesterases B1 and B2 (TbrPDEB1 and TbrPDEB2) play an important role in the life cycle of Trypanosoma brucei, the causative parasite of human African trypanosomiasis (HAT), also known as African sleeping sickness. We used homology modeling and docking studies to guide fragment growing into the parasite-specific P-pocket in the enzyme binding site. The resulting catechol pyrazolinones act as potent TbrPDEB1 inhibitors with IC₅₀ values down to 49 nM. The compounds also block parasite proliferation (e.g., VUF13525 (20b): T. brucei rhodesiense IC₅₀ = 60 nM, T. brucei brucei IC₅₀ = 520 nM, T. cruzi = 7.6 μM), inducing a typical multiple nuclei and kinetoplast phenotype without being generally cytotoxic. The mode of action of 20b was investigated with recombinantly engineered trypanosomes expressing a cAMP-sensitive FRET sensor, confirming a dose-response related increase of intracellular cAMP levels in trypanosomes. Our findings further validate the TbrPDEB family as antitrypanosomal target.

Simple Colorimetric Trypanothione Reductase-Based Assay for High-Throughput Screening of Drugs against Leishmania Intracellular Amastigotes

“…alamarBlue was purchased from AbD Serotec (Düsseldorf, Germany). The test compounds (VUF series of cathecolpyrazolinones and the dibenzylmethylene amine derivative IOTA 0058) are proprietary compounds of the VU University, Amsterdam, the Netherlands, and were provided within the framework of a collaborative project for development of new phosphodiesterase inhibitors (T4-302; TIPharma) (25). Amphotericin B and sodium stibogluconate were purchased from Merck KGaA (Darmstadt, Germany).…”

Current Screening Methodologies in Drug Discovery for Selected Human Diseases

“…PDE is an essential protein for the proliferation of the parasite [73]. The enzyme regulates cyclic nucleotide levels and induces the cessation of the parasite cell division, with consequent lysis and control of the infection in a mouse model [74]. Additionally, the human PDE type 4D (hPDE4D) activity should be assayed in parallel for the compounds screened to avoid off-target effects.…”

Fluorous Supported Synthesis of Pyrazolone Derivatives From Allylic Alcohols Using a Palladium-Catalyzed Strategy

“…To a 3, 3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl--acrylate (2 g, 3.86 mmol, 1 eq) was added DABCO (490 mg, 3.86 mmol, 1 eq) and 2 eq of aldehyde (R 1 CHO) in neat conditions. After stirring at room temperature for 48 h, the crude reaction mixture is diluted in CH 2 Cl 2 (30 mL), washed three times with water and dried over anhydrous sodium sulphate.…”