Identification of a novel, non-tetrahydroquinoline variant of the cholesteryl ester transfer protein (CETP) inhibitor torcetrapib, with improved aqueous solubility.

1. Elaborate studies of cholesteryl ester transfer protein (CETP) polymorphisms and genetic deficiency in humans suggest direct links between CETP, high-density lipoprotein cholesterol (HDL-c) levels and coronary heart diseases. The hypothesis that CETP inhibition by small molecule inhibitors raises HDL-c has been validated clinically with structurally-diverse CETP inhibitors such as torcetrapib, anacetrapib, dalcetrapib and evacetrapib. 2. Despite promising phase 2 results with respect to HDL-c elevation, torcetrapib was discontinued in phase 3 trials due to increased mortality rates in the cardiovascular outcomes study. Emerging evidence for the adverse effects hints at off-target chemotype-specific cardiovascular toxicity, possibly related to the pressor effects of torcetrapib, since structurally diverse CETP inhibitors such as anacetrapib, evacetrapib and dalcetrapib are not associated with blood pressure increases in humans. Nonclinical follow-up studies showed that torcetrapib induces aldosterone biosynthesis and secretion in vivo and in vitro, an effect which is not observed with other CETP inhibitors in clinical development. 3. As part of ongoing efforts to identify novel CETP inhibitors devoid of pressor effects, strategies were implemented towards the design of compounds, which lack the 1,2,3,4-tetrahydroquinoline (THQ) scaffold present in torcetrapib. In this article, we disclose results of structure-activity relationship studies for a series of novel non-THQ CETP inhibitors, which resulted in the identification of a novel isonipecotic acid derivative 10 (also referred to as PF-04445597) with vastly improved oral pharmacokinetic properties mainly as a result of improved aqueous solubility. This feature is attractive in that, it bypasses significant investments needed to develop compatible solubilizing formulation(s) for oral drug delivery of highly lipophilic and poorly soluble compounds; attributes, which are usually associated with small molecule CETP inhibitors. PF-04445597 was also devoid of aldosterone secretion in human H295R adrenal carcinoma cells.

Design, synthesis and biological evaluation of α-substituted isonipecotic acid benzothiazole analogues as potent bacterial type II topoisomerase inhibitors.

The discovery and optimisation of a new class of benzothiazole small molecules that inhibit bacterial DNA gyrase and topoisomerase IV are described. Antibacterial properties have been demonstrated by activity against DNA gyrase ATPase and potent activity against Staphylococcus aureus, Enterococcus faecalis, Streptococcus pyogenes and Haemophilus influenzae. Further refinements to the scaffold designed to enhance drug-likeness included analogues bearing an α-substituent to the carboxylic acid group, resulting in excellent solubility and favourable pharmacokinetic properties.

Discovery of potent pteridine reductase inhibitors to guide antiparasite drug development.

Pteridine reductase (PTR1) is essential for salvage of pterins by parasitic trypanosomatids and is a target for the development of improved therapies. To identify inhibitors of Leishmania major and Trypanosoma cruzi PTR1, we combined a rapid-screening strategy using a folate-based library with structure-based design. Assays were carried out against folate-dependent enzymes including PTR1, dihydrofolate reductase (DHFR), and thymidylate synthase. Affinity profiling determined selectivity and specificity of a series of quinoxaline and 2,4-diaminopteridine derivatives, and nine compounds showed greater activity against parasite enzymes compared with human enzymes. Compound 6a displayed a K(i) of 100 nM toward LmPTR1, and the crystal structure of the LmPTR1:NADPH:6a ternary complex revealed a substrate-like binding mode distinct from that previously observed for similar compounds. A second round of design, synthesis, and assay produced a compound (6b) with a significantly improved K(i) (37 nM) against LmPTR1, and the structure of this complex was also determined. Biological evaluation of selected inhibitors was performed against the extracellular forms of T. cruzi and L. major, both wild-type and overexpressing PTR1 lines, as a model for PTR1-driven antifolate drug resistance and the intracellular form of T. cruzi. An additive profile was observed when PTR1 inhibitors were used in combination with known DHFR inhibitors, and a reduction in toxicity of treatment was observed with respect to administration of a DHFR inhibitor alone. The successful combination of antifolates targeting two enzymes indicates high potential for such an approach in the development of previously undescribed antiparasitic drugs.

Synthesis and inotropic evaluation of 1-substituted-N-(4,5-dihydro-1-methyl-[1,2,4]triazolo[4,3-a]quinolin-7-yl)piperidine-4-carboxamides.

A series of 1-substituted-N-(4,5-dihydro-1-methyl-[1,2,4]triazolo[4,3-a]quinolin-7-yl) piperidine-4-carboxamides has been synthesized and evaluated for positive inotropic activity by measuring left atrium stroke volume in isolated rabbit-heart preparations. Some of these derivatives exhibited favorable activity compared with the standard drug, milrinone, among which 1-(2-fluorobenzyl)-N-(4,5-dihydro-1-methyl-[1,2,4]triazolo[4,3-a]quinolin-7-yl)piperidine-4-carboxamide 6a was the most potent, increasing stroke volume by 11.92+/-0.35% (milrinone: 6.36+/-0.13%) at 1x10(-4)M.

Modifications of the isonipecotic acid fragment of SNS-032: analogs with improved permeability and lower efflux ratio.

Modifications of the isonipecotic acid fragment of SNS-032 results in analogs which are more permeable and lower effluxed than SNS-032. The enantiomerically pure synthesis and the in vivo profile of analog 20 is described.

Simultaneous analysis of five antidepressant drugs using direct injection of biofluids in a capillary restricted-access media-liquid chromatography-tandem mass spectrometry system.

Direct analysis, with minimal sample pretreatment, of antidepressant drugs, fluoxetine, imipramine, desipramine, amitriptyline, and nortriptyline in biofluids was developed with a total run time of 8 min. The setup consists of two HPLC pumps, injection valve, capillary RAM-ADS-C18 pre-column and a capillary analytical C18 column connected by means of a six-port valve in backflush mode. Detection was performed with ESI-MS/MS and only 1 microm of sample was injected. Validation was adequately carried out using FLU-d(5) as internal standard. Calibration curves were constructed under a linear range of 1-250 ng mL(-1) in plasma, being the limit of quantification (LOQ), determined as 1 ng mL(-1), for all the analytes. With the described approach it was possible to reach a quantified mass sensitivity of 0.3 pg for each analyte (equivalent to 1.1-1.3 fmol), translating to a lower sample consumption (in the order of 10(3) less sample than using conventional methods).

Differential pulse cathodic voltammetric determination of floctafenine and metopimazine.

A simple, rapid and sensitive voltammetric method for the determination of floctafenine (FFN) and metopimazine (MPZ) was developed. Well-defined cathodic waves were obtained for both drugs in Britton-Robinson buffer pH 9.0 using the differential-pulse mode at the hanging mercury drop electrode (HMDE). The current-concentration relationship was found to be linear over the ranges 0.4-3.6 and 0.4-2.4 microg ml(-1) for FFN and MPZ, respectively. The quantification of the two drugs in their pharmaceutical formulations was carried out using the proposed voltammetric method and compared with spectrophotometric analysis data. The mechanisms of the electrode reactions for the two drugs were proposed.

Electronic-topological study of the structure-activity relationships in a series of piperidine morphinomimetics.

Structure-activity relationships (SAR) are studied in the series of 4,4-disubstituted piperidine morphinomimetics (42 compounds) by means of the Electronic-Topological Method (ETM). In the frameworks of this approach, its input data were taken as the results of conformational and quantum-mechanical calculations. These calculations had been carried out for all compounds from the series under study, taking into account their neutral and protonated by the nitrogen of piperidine cycle forms. The ETM application resulted in a set of pharmacophores and anti-pharmacophores, which formed a basis of a system used to predict analgesic activity. First of all, the system was tested on known analgesics. Testing has shown a good agreement with the experimental data. Then, the system was applied to a few compounds with similar structures but unknown activity. The results of the study could be used for computer screening and design of novel compounds with analgesics properties as new potential drugs.

Phosphinic, phosphonic and seleninic acid bioisosteres of isonipecotic acid as novel and selective GABA(C) receptor antagonists.

A number of amino acids bioisosterically derived from the specific GABA(A) agonist, isonipecotic acid, were electrophysiologically characterized as antagonists at GABA(C) rho(1) receptors expressed in Xenopus oocytes. The phosphinic acid analogue of isonipecotic acid, piperidin-4-ylphosphinic acid (2), was comparable with the standard GABA(C) antagonist, (1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid (TPMPA), in terms of potency and GABA(C) versus GABA(A) receptor selectivity. Whereas the phosphonic acid analogue, piperidin-4-ylphosphonic acid (4), was at least an order of magnitude weaker than piperidin-4-ylphosphinic acid as a GABA(C) antagonist, the seleninic acid analogue, piperidin-4-ylseleninic acid (SEPI, 6), was the most potent and selective GABA(C) antagonist within the group of isonipecotic acid derived amino acids studied.

Highly water-soluble derivatives of the anesthetic agent propofol: in vitro and in vivo evaluation of cyclic amino acid esters.

Cyclic amino acid esters of propofol were synthesized in an attempt to develop new water-soluble anesthetic agents. Their solubility and stability in aqueous solution, and their ability to release propofol in vitro under physiological conditions were determined. L-Proline (6a) and racemic nipecotic acid (6c) esters were found to be highly soluble in water. Sufficiently stable at physiological pH (half-lives >6 h), the alpha-amino acid esters, 6a and 6b, were found to be quantitatively hydrolyzed in plasma and liver esterase solutions within a few minutes, showing prodrug behavior. The in vitro activity of the esters, determined either by the [(35)S]tert-butylbicyclophosphorothionate ([(35)S]TBPS) binding assay or electrophysiological measurements of the action at cloned human receptors, proved to be a mechanism involving allosteric modulation of GABA(A) receptors. Indeed, L-proline (6a), and racemic pipecolinate (6b) and nipecotate (6c), like propofol, reduced [(35)S]TBPS binding, whereas isonipecotate (6d) showed bicuculline-like behavior, increasing [(35)S]TBPS binding. A nonlinear relation between GABA(A) receptor binding affinity and lipophilicity, as assessed by reversed-phase high-performance liquid chromatography, emerged as a trend. The in vivo anticonvulsant and anesthetic activities of prolinate 6a, intraperitoneally administered in water solution, showed that is a water-soluble propofol prodrug candidate for developing formulations useful for parenteral administration.

Design, synthesis and anticonvulsive activities of potential prodrugs linked by two-carbon chain.

For the development of new anticonvulsive agents, GABAmimetics such as nipecotic acid, isonipecotic acid, gamma-aminobutyric acid (GABA), gamma-vinyl GABA (vigabatrin) and valproic acid were covalently coupled through an ester bond by a two-carbon linker chain as potential pro-drugs and evaluated for their anticonvulsive activities.

Design, synthesis and anticonvulsive activity of analogs of gamma-vinyl GABA.

For the development of new anticonvulsive agents, analogs of gamma-vinyl GABA (vigabatrin) containing GABA, gamma-vinyl GABA, valproic acid, nipecotic acid or isonipecotic acid moieties were prepared and evaluated for their anticonvulsive activities. Most of the prepared compounds showed moderate anticonvulsive activities. Among them compounds 10 and 16 displayed the most potent anticonvulsive activity and a broader spectrum compared to vigabatrin.

Fragmentation pathways of metopimazine and its metabolite using ESI-MS(n), HR-MS and H/D exchange.

Metopimazine (MPZ) is a phenothiazine derivative used to prevent emesis during chemotherapy where few structural analysis of the aforementioned compound have been described in the literature. Thus, this work reports, for the first time, the detailed study of fragmentation pathways of MPZ and its metabolite (AMPZ) using electrospray ionization (EI) with multistage mass spectrometry (ESI-MS(n)) in positive-ion mode. The structures of 21 product ions were identified and their accurate masses were determined using high resolution mass spectrometry (HRMS) experiments. Characteristic product ions of these two phenothiazine derivatives are more particularly displayed along with differences between their relative abundances and their structures checked by H/D exchange experiments.

Intercepting the synthesis of triazine dendrimers with nucleophilic pharmacophores: a general strategy toward drug delivery vehicles.

The camptothecin ester of isonipecotic acid is installed on a triazine dendrimer intermediate obtained through an iterative, scalable route to ultimately yield cationic and PEGylated targets with activities in cell culture comparable to free drug.

Facile synthesis of 4-substituted-4-aminopiperidine derivatives, the key building block of piperazine-based CCR5 antagonists.

4-Substituted-4-aminopiperidine is an interesting structural motif found in a number of bioactive compounds. An efficient and convenient method for the synthesis of 4-differently substituted-4-aminopiperidine derivatives was described, employing isonipecotate as a starting material and Curtius rearrangement as a key step. The alkylation of isonipecotate could introduce various substituents at the 4-position of the piperidine ring. With this key building block, we are able to efficiently synthesize piperazino-piperidine based CCR5 antagonist in a highly convergent manner free of using toxic reagents such as diethylaluminum cyanide. The concise synthesis of a potent bioavailable CCR5 antagonist as HIV-1 entry inhibitor, Sch-350634 (1) was accomplished in excellent yield using N'-Boc-4-methyl-4-aminopiperidine 5a as a smart building block. The new methodology provides a facile and practical access to the piperazino-piperidine amide analogs as HIV-1 entry inhibitors.

Design and synthesis of small semi-mimetic peptides with immunomodulatory activity based on myelin basic protein (MBP).

Experimental allergic encephalomyelitis (EAE) is induced in susceptible animals by immunodominant determinants of myelin basic protein (MBP). Analogs of these disease-associated peptides have been identified with disease progression upon coimmunization. Usage of peptides, with disease-specific immunomodulatory capacity in vivo is limited, however, due to their sensitivity to proteolytic enzymes. Alternative approaches include the development of mimetic molecules which maintain the biological function of an original peptide, yet are stable and able to elicit their response in pharmacological quantities. A novel technique was employed to design a series of semi-mimetic peptides, based on the guinea pig MBP72-85 peptide used to induce EAE in Lewis rats. We used isonipecotic (iNip) and aminocaproic (Acp) acids as templates. Acp-MBP72-85 peptide derived analogues were effective in inducing EAE compared to iNip-peptide analogues which were ineffective at 350 micrograms. These findings suggest that the design and synthesis of semi-mimetic peptide molecules with immunomodulatory potential is possible and that eventually these molecules may form the basis for the development of novel and more effective disease-specific therapeutic agents.

Synthesis and antinociceptive activity of ring substituted N-[(2-phenyl-2-hydroxy)ethyl]-4-phenyl-4-carboethoxypiperidines.

A series of phenyl substituted N-[(2-phenyl-2-hydroxy)ethyl]-4-phenyl-4-carboethoxylpiperidine were synthesized and their antinociceptive activity tested in mice and compared with morphine sulphate. All compounds demonstrated antinociceptive activity in both the hot plate and the writhing tests. The studies showed that the antinociceptive activity is dependable on both the nature and the position of the substituent on the phenyl ring. Antagonism study with naloxone suggests possible interaction of the new compounds with the opioid receptors.