James V. Pivnichny

Anthrax lethal factor inhibition

The primary virulence factor of Bacillus anthracis is a secreted zinc-dependent metalloprotease toxin known as lethal factor (LF) that is lethal to the host through disruption of signaling pathways, cell destruction, and circulatory shock. Inhibition of this proteolytic-based LF toxemia could be expected to provide therapeutic value in combination with an antibiotic during and immediately after an active anthrax infection. Herein is shown the crystal structure of an intimate complex between a hydroxamate, (2R)-2-[(4-fluoro-3-methylphenyl)sulfonylamino]-N-hydroxy-2-(tetrahydro-2H-pyran-4-yl)acetamide, and LF at the LF-active site. Most importantly, this molecular interaction between the hydroxamate and the LF active site resulted in (i) inhibited LF protease activity in an enzyme assay and protected macrophages against recombinant LF and protective antigen in a cell-based assay, (ii) 100% protection in a lethal mouse toxemia model against recombinant LF and protective antigen, (iii) ≈50% survival advantage to mice given a lethal challenge of B. anthracis Sterne vegetative cells and to rabbits given a lethal challenge of B. anthracis Ames spores and doubled the mean time to death in those that died in both species, and (iv) 100% protection against B. anthracis spore challenge when used in combination therapy with ciprofloxacin in a rabbit “point of no return” model for which ciprofloxacin alone provided 50% protection. These results indicate that a small molecule, hydroxamate LF inhibitor, as revealed herein, can ameliorate the toxemia characteristic of an active B. anthracis infection and could be a vital adjunct to our ability to combat anthrax.

Liquid chromatographic determination of ivermectin in animal plasma with trifluoroacetic anhydride and N-methylimidazole as the derivatization reagent

Ivermectin is a potent anthelmintic agent which was detected at low concentrations in cattle plasma by LC after conversion to a fluorescent derivative. This was accomplished by reaction with acetic anhydride (AA) and pyridine for 24 h at 100 degrees C or with AA and N-methylimidazole (NMIM) for 1 h at 95 degrees C. Substituting trifluoroacetic anhydride (TFAA) for AA reduced the reaction time to less than 30 s at 25 degrees C, yielding an intensely fluorescent derivative with substantially fewer reagent by-products. The need for further sample preparation after derivatization with TFAA-NMIM was thereby eliminated, and detection limits of less than 20 pg ml-1 ivermectin could be achieved with 1 ml of plasma by a considerably simpler analytical procedure.

Potent, orally absorbed glucagon receptor antagonists.

The SAR of 2-pyridyl-3,5-diaryl pyrroles, ligands of the human glucagon receptor and inhibitors of p38 kinase, were investigated. This effort resulted in the identification of 2-(4-pyridyl)-5-(4-chlorophenyl)-3-(5-bromo-2-propyloxyphenyl)pyrr ole 49 (L-168,049), a potent (Kb = 25 nM), selective antagonist of glucagon.

Design and synthesis of potent, orally bioavailable dihydroquinazolinone inhibitors of p38 MAP kinase.

The development of potent, orally bioavailable (in rat) and selective dihydroquinazolinone inhibitors of p38alpha MAP kinase is described. These analogues are hybrids of a pyridinylimidazole p38alpha inhibitor reported by Merck Research Laboratories and VX-745. Optimization of the C-5 phenyl and the C-7 piperidinyl substituents led to the identification of 15i which gave excellent suppression of TNF-alpha production in LPS-stimulated whole blood (IC(50)=10nM) and good oral exposure in rats (F=68%, AUCn PO=0.58 microM h).

Biphenyl-Substituted Oxazolidinones as Cholesteryl Ester Transfer Protein Inhibitors: Modifications of the Oxazolidinone Ring Leading to the Discovery of Anacetrapib

The development of the structure-activity studies leading to the discovery of anacetrapib is described. These studies focused on varying the substitution of the oxazolidinone ring of the 5-aryloxazolidinone system. Specifically, it was found that substitution of the 4-position with a methyl group with the cis-stereochemistry relative to the 5-aryl group afforded compounds with increased cholesteryl ester transfer protein (CETP) inhibition potency and a robust in vivo effect on increasing HDL-C levels in transgenic mice expressing cynomolgus monkey CETP.

2-Arylbenzoxazoles as CETP inhibitors: raising HDL-C in cynoCETP transgenic mice.

We describe structure-activity studies leading to the discovery of 2-arylbenzoxazole 3, the first in a series to raise serum high-density lipoprotein cholesterol levels in transgenic mice. Replacement of the 4-piperidinyloxy moiety with piperazinyl provided a more synthetically tractable lead, which upon optimization resulted in compound 4, an excellent inhibitor of cholesteryl ester transfer protein function with good pharmacokinetic properties and in vivo efficacy.

Characterization of a technique for rapid pharmacokinetic studies of multiple co-eluting compounds by LC/MS/MS

A method for rapid pharmacokinetic screening of multiple potential drug candidates has been developed. This technique, based on the ability of liquid chromatography coupled with tandem mass spectrometry (LC/MS/MS) to independently monitor multiple components, enables the quantification of substances which may or may not be chromatographically resolved. Our results indicate that the limit of quantitation and accuracy of this multiple-compound LC/MS/MRM quantitation method are comparable to a single-compound LC/MS/MRM quantitation method. No apparent ion suppression due to the existence of extraneous compounds in the analytical solution and biological matrix effect are observed in the range of the calibration curve. The issue of potential residual molecule cross-talk interference existing in the multiple-reaction monitoring mode has been discussed. This multiple-compound LC/MS/MRM quantitation method can be used for high throughput pharmacokinetic screening and to assay mixtures that have co-eluting analytes or similar m/z of precursor/product ion pairs.

A tacrolimus-related immunosuppressant with reduced toxicity

BACKGROUND Tacrolimus (FK506) has potent immunosuppressive properties reflecting its ability to block the transcription of lymphokine genes in activated T cells through formation of a complex with FK506 binding protein-12, which inhibits the phosphatase activity of calcineurin. The clinical usefulness of tacrolimus is limited, however, by severe adverse effects, including neurotoxicity and nephrotoxicity. Although this toxicity, like immunosuppression, appears mechanistically related to the calcineurin inhibitory action of the drug, a large chemistry effort has been devoted to search for tacrolimus analogs with reduced toxicity but preserved immunosuppressive activity that might have enhanced therapeutic utility. METHODS Here, we report on the identification of such an analog, which was synthetically derived from ascomycin (ASC), the C21 ethyl analog of tacrolimus, by introducing an indole group at the C32 position. The profile of biological activity of indolyl-ASC was characterized in rodent models of immunosuppression and toxicity. RESULTS Indolyl-ASC was found to exhibit an immunosuppressive potency equivalent to that of tacrolimus in T-cell activation in vitro and in murine transplant models, even though indolyl-ASC bound about 10 times less to intracellular FK506 binding protein-12 than tacrolimus or ASC. Further evaluation of indolyl-ASC revealed that it is threefold less potent than tacrolimus in inducing hypothermia, a response that may reflect neurotoxicity, and in causing gastrointestinal transit alterations in mice. Moreover, indolyl-ASC was at least twofold less nephrotoxic than tacrolimus upon 3-week oral treatment in rats. CONCLUSIONS Altogether, these data indicate a modest but definite improvement in the therapeutic index for indolyl-ASC compared with tacrolimus in rodent models.

2-Arylbenzoxazoles as CETP inhibitors: Substitution and modification of the α-alkoxyamide moiety

The development of a series of 2-arylbenzoxazole alpha-alkoxyamide and beta-alkoxyamine inhibitors of cholesteryl ester transfer protein (CETP) is described. Highly fluorinated alpha-alkoxyamides proved to be potent inhibitors of CETP in vitro, and the highly fluorinated 2-arylbenzoxazole beta-alkoxyamine 4 showed a desirable combination of in vitro potency (IC(50)=151 nM) and oral bioavailability in the mouse.

Discovery of N-{N-[(3-cyanophenyl)sulfonyl]-4(R)-cyclobutylamino-(L)-prolyl}-4-[(3',5'-dichloroisonicotinoyl) amino]-(L)-phenylalanine (MK-0668), an extremely potent and orally active antagonist of very late antigen-4.

Extremely potent very late antigen-4 (VLA-4) antagonists with picomolar, whole blood activity and slow dissociation rates were discovered by incorporating an amino substituent on the proline fragment of the initial lead structure. This level of potency against the unactivated form of VLA-4 was shown to be sufficient to overcome the poor pharmacokinetic profiles typical of this class of VLA-4 antagonists, and sustained activity as measured by receptor occupancy was achieved in preclinical species after oral dosing.