Identification and Characterization of Small Molecule Inhibitors of a Class I Histone Deacetylase from Plasmodium falciparum

A library of approximately 2000 small molecules biased toward inhibition of histone deacetylases was assayed for antimalarial activity in a high-throughput P. falciparum viability assay. Active compounds were cross-analyzed for induction of histone hyperacetylation in a human myeloma cell line to identify HDAC inhibitors with selectivity for P. falciparum over the human host. To verify on-target selectivity, pfHDAC-1 was expressed and purified and a biochemical assay for pfHDAC-1 activity was established.Chemistry and Chemical Biolog

Proazaphosphatranes: a highly effective class of triaminophosphine ligands in palladium-catalyzed cross-coupling reactions

In recent years proazaphosphatranes of type P(RNCH2CH 2)3N have proven their synthetic utility as catalysts and as stoichiometric bases in a variety of organic transformations. Herein are described their application as a supporting ligand for palladium in palladium-catalyzed cross-coupling reactions, such as Buchwald-Hartwig amination, Stille, and Suzuki reactions.;Screening of various proazaphosphatranes (R = Me, Et, i-Pr, i-Bu, neo-Pent) revealed that the electron-rich, bulky, and commercially available P(i-BuNCH2CH 2)3N is the most effective ligand of this series in the aforementioned reactions. Aryl halides (bromides and iodides), including notoriously unreactive aryl chlorides, have been shown to participate in these processes.;It has also been discovered that for certain combinations of substrates in palladium-catalyzed Stille reactions, the proazaphosphatranes P(PhCH 2NCH2CH2)3N and P(PhCH2NCH 2CH2)2N(i-BuNCH2CH 2) provided even more active palladium catalysts than P(i-BuNCH 2CH2)3N.;Additionally, the synthesis of the new bicyclic triaminophosphine ligand P(i-BuNCH2)3CMe and its efficacy in Buchwald-Hartwig amination reactions is demonstrated. This ligand provides a remarkably general, efficient, and mild palladium catalyst for aryl iodide amination. This ligand also allows a weak base, such as Cs2CO 3, to function in these reactions.;Finally, the first general protocol for the ligand-, copper-, and amine-free Sonogashira reaction has been developed. The success of this method hinges on the use of tetrabutylammonium acetate as the base.</p

Discovery and Characterization of Potent Dual P-Glycoprotein and CYP3A4 Inhibitors: Design, Synthesis, Cryo-EM Analysis, and Biological Evaluations

Targeted concurrent inhibition of intestinal drug efflux transporter P-glycoprotein (P-gp) and drug metabolizing enzyme cytochrome P450 3A4 (CYP3A4) is a promising approach to improve oral bioavailability of their common substrates such as docetaxel, while avoiding side effects arising from their pan inhibitions. Herein, we report the discovery and characterization of potent small molecule inhibitors of P-gp and CYP3A4 with encequidar (minimally absorbed P-gp inhibitor) as a starting point for optimization. To aid in the design of these dual inhibitors, we solved the high-resolution cryo-EM structure of encequidar hound to human P-gp. The structure guided us to prudently decorate the encequidar scaffold with CYP3A4 pharmacophores, leading to the identification of several analogues with dual potency against P-gp and CYP3A4. In vivo, dual P-gp and CYP3A4 inhibitor 3a improved the oral absorption of docetaxel by 3-fold as compared to vehicle, while 3a itself remained poorly absorbed.ISSN:1520-4804ISSN:0022-262

Aminoindoles, a Novel Scaffold with Potent Activity against Plasmodium falciparum▿†

This study characterizes aminoindole molecules that are analogs of Genz-644442. Genz-644442 was identified as a hit in a screen of ∼70,000 compounds in the Broad Institute's small-molecule library and the ICCB-L compound collection at Harvard Medical School. Genz-644442 is a potent inhibitor of Plasmodium falciparum in vitro (50% inhibitory concentrations [IC50s], 200 to 285 nM) and inhibits P. berghei in vivo with an efficacy of >99% in an adapted version of Peters' 4-day suppressive test (W. Peters, Ann. Trop. Med. Parasitol. 69:155–171, 1975). Genz-644442 became the focus of medicinal chemistry optimization; 321 analogs were synthesized and were tested for in vitro potency against P. falciparum and for in vitro absorption, distribution, metabolism, and excretion (ADME) properties. This yielded compounds with IC50s of approximately 30 nM. The lead compound, Genz-668764, has been characterized in more detail. It is a single enantiomer with IC50s of 28 to 65 nM against P. falciparum in vitro. In the 4-day P. berghei model, when it was dosed at 100 mg/kg of body weight/day, no parasites were detected on day 4 postinfection. However, parasites recrudesced by day 9. Dosing at 200 mg/kg/day twice a day resulted in cures of 3/5 animals. The compound had comparable activity against P. falciparum blood stages in a human-engrafted NOD-scid mouse model. Genz-668764 had a terminal half-life of 2.8 h and plasma trough levels of 41 ng/ml when it was dosed twice a day orally at 55 mg/kg/day. Seven-day rat safety studies showed a no-observable-adverse-effect level (NOAEL) at 200 mg/kg/day; the compound was not mutagenic in Ames tests, did not inhibit the hERG channel, and did not have potent activity against a broad panel of receptors and enzymes. Employing allometric scaling and using in vitro ADME data, the predicted human minimum efficacious dose of Genz-668764 in a 3-day once-daily dosing regimen was 421 mg/day/70 kg, which would maintain plasma trough levels above the IC90 against P. falciparum for at least 96 h after the last dose. The predicted human therapeutic index was approximately 3, on the basis of the exposure in rats at the NOAEL. We were unable to select for parasites with >2-fold decreased sensitivity to the parent compound, Genz-644442, over 270 days of in vitro culture under drug pressure. These characteristics make Genz-668764 a good candidate for preclinical development