Antimalarial bicyclic peroxides belonging to the G-factor family: mechanistic aspects of their formation and iron (II) induced reduction.

Artemisinin and its derivatives are peroxide-containing compounds targeting P. falciparum. We review here structural analogues of bicyclic peroxides belonging to the G factors family presenting antimalarial properties. They were synthesised under Mannich type conditions, followed by an autoxidation step resulting exclusively in the peroxide. As the electron transfer from haem or free iron to the peroxide is the first step in the mode of action of artemisinin-like compounds, the redox properties of some endoperoxides were studied by electrochemistry allowing the evaluation of the reduction standard potentials. The Fe(II) induced reduction was also investigated and the reactivity of the C-centered radical intermediate formed was linked to the antimalarial activity. These bicyclic peroxides both with various hybrid molecules containing the endoperoxide framework were evaluated in vitro against Plasmodium falciparum. They exhibited moderate to good activities.

Hydrolytic pathway of 5-fluorouracil in aqueous solutions for clinical use.

The purpose of the study was to investigate the degradation pathway of 5-fluorouracil (FU) in the situation of commercial formulations for clinical use, namely FU dissolved in sodium hydroxide (NaOH) solutions or Tris buffer at pH 8.5-9. Combination of data from (19)F, (1)H and (13)C NMR and in some cases MS led to the identification of 8 and 13 FU degradation products in NaOH and Tris solutions respectively. In FU NaOH solutions, the first stage of FU degradation is a stereoselective hydration of the C5-C6 double bond leading to 5,6-dihydro-5-fluoro-6-hydroxyuracil, the cis stereoisomer being predominant relative to the trans. The second stage involves either a defluorination step with formation of fluoride ion and 5-hydroxyuracil or the cleavage of the N3-C4 bond giving the two diastereoisomeric 2-fluoro-3-hydroxy-3-ureidopropanoic acids. The subsequent N1-C6 bond breakdown of these compounds releases urea and 2-fluoro-3-oxopropanoic acid (FOPA) which in turn losses easily carbon dioxide leading to the formation of fluoroacetaldehyde (Facet). The degradation pathway in FU-Tris solutions is identical, except that Tris reacts with the aldehydes FOPA and Facet to form oxazolidine adducts stable at pH 8.5 but in equilibrium with the aldehyde forms at physiological pH, whereas the high reactivity of free aldehydes leads to numerous unidentified degradation compounds all in very low amounts. The FOPA diastereoisomeric adducts react with Facet to form four diastereoisomeric fused bicyclic five-membered ring compounds. Facet and FOPA are highly cardiotoxic. In Tris formulations, they are trapped as stable oxazolidine adducts which release the free aldehydes at physiological pH thus explaining the higher cardiotoxicity of FU in Tris solutions compared to that of FU in NaOH solutions.

Distinct CCK-2 receptor conformations associated with ß-arrestin-2 recruitment or phospholipase-C activation revealed by a biased antagonist.

Seven-transmembrane receptors (7TMRs), also termed G protein-coupled receptors (GPCRs), form the largest class of cell surface membrane receptors, involving several hundred members in the human genome. Nearly 30% of marketed pharmacological agents target 7TMRs. 7TMRs adopt multiple conformations upon agonist binding. Biased agonists, in contrast to non-biased agonists, are believed to stabilize conformations preferentially activating either G-protein- or ß-arrestin-dependent signaling pathways. However, proof that cognate conformations of receptors display structural differences within their binding site where biased agonism initiates, are still lacking. Here, we show that a non-biased agonist, cholecystokinin (CCK) induces conformational states of the CCK2R activating Gq-protein-dependent pathway (CCK2R(G)) or recruiting ß-arrestin2 (CCK2R(ß)) that are pharmacologically and structurally distinct. Two structurally unrelated antagonists competitively inhibited both pathways. A third ligand (GV150013X) acted as a high affinity competitive antagonist on CCK2R(G) but was nearly inefficient as inhibitor of CCK2R(ß). Several structural elements on both GV150013X and in CCK2R binding cavity, which hinder binding of GV150013X only to the CCK2R(ß) were identified. At last, proximity between two conserved amino acids from transmembrane helices 3 and 7 interacting through sulfur-aromatic interaction was shown to be crucial for selective stabilization of the CCK2R(ß) state. These data establish structural evidence for distinct conformations of a 7TMR associated with ß-arrestin-2 recruitment or G-protein coupling and validate relevance of the design of biased ligands able to selectively target each functional conformation of 7TMRs.

Synthesis of lipophilic dimeric C-7/C-7-linked ciprofloxacin and C-6/C-6-linked levofloxacin derivatives. Versatile in vitro biological evaluations of monomeric and dimeric fluoroquinolone derivatives as potential antitumor, antibacterial or antimycobacterial agents.

The synthesis of C-7/C-7-linked ciprofloxacin (CP) and C-6/C-6-linked levofloxacin (LV) derivatives with modulated lipophilicity is described herein. The synthesized compounds, along with the monomeric analogs described previously, were evaluated in vitro for (i) their growth inhibitory effect against five human cancer cell lines, (ii) their antibacterial activity against Gram-positive Staphylococcus aureus and Enterococcus hirae and Gram-negative Escherichia coli and Pseudomonas aeruginosa strains and (iii) their antimycobacterial activity. The most efficient derivatives as antiproliferative agents (C-7/C-7-linked CP 7e and C-6/C-6-linked LV 11f) displayed IC(50) values in the 0.1-8.7 and 0.2-0.7 µM ranges respectively while IC(50) values for parent CP and LV ranged from 89 to 476 µM and from 67 to 622 µM respectively depending on the cell line. A specific antibacterial activity against S. aureus was found for the monomeric and dimeric derivatives of CP. The most efficient derivative against S. aureus (monomeric oxoethyloctanoate CP derivative 3d) displayed MIC <1 nM. Monomeric alkanoyloxymethyl LV esters (9a,c,e,f) and C-6/C-6-linked LV derivatives (11f-h) were the most efficient derivatives as antimycobacterial agents with MIC and IC(50) values in the 2.5-5 µM and 1.3-≤ 2.5 µM ranges respectively while MIC and IC(50) values for parent LV were 2.5 and 0.8 µM, respectively.

Novel lipophilic 7H-pyrido[1,2,3-de]-1,4-benzoxazine-6-carboxylic acid derivatives as potential antitumor agents: improved synthesis and in vitro evaluation.

A convenient route for the synthesis of some acyloxymethyl esters and carboxamides of levofloxacin (LV) with modulated lipophilicity is described. The synthesized compounds were evaluated in vitro for their growth inhibitory effect in five human cancer cell lines. The most efficient LV derivatives (ester 2e and amide 4d) displayed IC(50) values in the 0.2-2.2 µM range, while IC(50) values for parent LV ranged between 70 and 622 µM depending on the cell line. The esters displayed no in vivo toxicity up to 80 mg/kg when administered intraperitoneally. This study thus shows that LV analogs displayed antitumor efficacy, at least in vitro, a feature that appeared to be independent from the lipophilicity of the grafted substituent.

7-((4-Substituted)piperazin-1-yl) derivatives of ciprofloxacin: synthesis and in vitro biological evaluation as potential antitumor agents.

Ciprofloxacin (CP), an antibiotic has been shown to have antiproliferative and apoptotic activities in several cancer cell lines. Moreover, several reports have highlighted the interest of increasing the lipophilicity to improve the antitumor efficacy. These studies have led us to synthesize new CP derivatives of various lipophilicities and to evaluate their activity in five human cancer cell lines. With an easy and cost-efficient procedure, 31 7-((4-substituted)piperazin-1-yl) derivatives of CP were prepared that displayed IC(50) values ranging from microM to mM concentrations and are non-toxic in vivo in healthy mice as shown by their maximal tolerated dose (MTD) indices >80 mg/kg. Several derivatives displayed higher in vitro antitumor activity than parent CP however this was not dependent on the lipophilicity of the substituent. Among all synthesized derivatives, the most potent were 2 and 6h whose IC(50) values were 10 microM in three (derivative 2) or four (derivative 6h) cancer cell lines.

Efficient approach to acyloxymethyl esters of nalidixic acid and in vitro evaluation as intra-ocular prodrugs.

Various alkylcarbonyloxymethyl esters of nalidixic acid ranging from 3 to 15 carbon units in the pro-moiety have been prepared and assessed as potential prodrugs. Their chromatographic retention factors k', silicone oil solubilities and in vitro conversion to nalidixic acid by a commercial esterase were determined together with their in vitro antimicrobial activity and cytotoxicity. The preliminary results suggest that silicone oil may have potential for the intra-ocular delivery of antibacterial compounds. Moreover, the in vitro release rate can be controlled by the lipophilicity of the prodrug.

Quantum chemistry-based interpretations on the lowest triplet state of luminescent lanthanides complexes. Part 1. Relation between the triplet state energy of hydroxamate complexes and their luminescence properties.

In this paper, we evaluate the potential use of theoretical calculations to obtain an energy scale of the lowest ligand-centred triplet excited state in luminescent terbium(III) complexes. In these complexes, non-radiative deactivation of the terbium emitting state via a back-energy transfer process (T1<--Tb(5D4)) is a common quenching process. Consequently the prediction of the energy gap between these two excited states should be useful for programming highly luminescent Tb(III) systems. We report on a strategy based upon experimental and theoretical investigations of the excited state properties of a series of four simple aromatic hydroxamate ligands coordinated to Tb(III) and Gd(III) ions. By using previously reported crystallographic data, the structural and energies properties of these systems were investigated in the ground and first excited triplet states at the density functional theory (DFT) level of calculations. Our theoretical results are consistent with a triplet excited state T1 which is localised on one ligand only and whose the energy level is independent of the lanthanide ion nature (Tb(III), Gd(III)). A good agreement between the calculated adiabatic transition energies and experimental data derived from emission spectra is obtained when a corrective term is considered. These satisfactory results are an indication that this type of modelling can lead to discriminate in terms of the position of the lowest ligand triplet energy level the best antenna among a family of chromophoric compounds. In addition this theoretical approach has provided indications that the difference between the adiabatic transition energies of all the investigated complexes can be mainly explained by metal-ligand electrostatic interactions. The influence of the number of antennae on the quantum yield and the luminescence lifetime is discussed.

Dexamethasone as a probe for docetaxel clearance.

PURPOSE: A pilot study was conducted in 23 patients in order to assess the correlation between docetaxel clearance (CL) and pharmacokinetics of dexamethasone. Dexamethasone is mainly 6-beta hydroxylated by CYP3A4, and is regularly used as standard docetaxel premedication. Genotyping of known functional single nucleotide polymorphism (SNP) of CYP3A5 (G22893A) and mdr-1 (G2677T, G2677A, and C3435T) have been performed in order to tentatively correlate genotype with docetaxel and dexamethasone pharmacokinetics. PATIENTS AND METHODS: To be eligible for this study, patients were required to have a solid malignancy for which docetaxel was indicated. A population pharmacokinetic approach was used to determine individual pharmacokinetic parameters of both docetaxel and dexamethasone by Bayesian analysis, and to screen relationships between docetaxel CL and patients' demographic, phenotype and genotype covariates. RESULTS: Three different pharmacokinetic parameters of dexamethasone were significantly correlated with docetaxel CL: dexamethasone plasma clearance (DPC) that ranged between 7.7 and 27.2 l/h, urinary amount of 6beta-hydroxydexamethasone, and the ratio between urinary amount of 6beta-hydroxydexamethasone and unchanged dexamethasone. The best covariate model was docetaxel CL (l/h) = 356 x fu(alpha1-AG) x (1-0.17 x HPMT)(1+0.126 x DPC) where fu(alpha1-AG) is the unbound plasma fraction of docetaxel calculated from alpha1-acid glycoprotein plasma level, and HPMT is hepatic metastasis coded as 1 if present or 0 if absent. No significant difference in docetaxel CL was observed between the several genotypes. CONCLUSIONS: Dexamethasone may be used as a probe to predict docetaxel clearances, hence reducing interindividual variability.