ABSTRACT
The synthesis, structure-activity relationships, and biological properties of a novel series of imidazole-containing inhibitors of farnesyltransferase are described. Starting from a 3-aminopyrrolidinone core, a systematic series of modifications provided 5h, a non-thiol, non-peptide farnesyltransferase inhibitor with excellent bioavailability in dogs. Compound 5h was found to have an unusually favorable ratio of cell potency to intrinsic potency, compared with other known FTIs. It exhibited excellent potency against a range of tumor cell lines in vitro and showed full efficacy in the K-rasB transgenic mouse model.
Subject(s)
Alkyl and Aryl Transferases/antagonists & inhibitors , Antineoplastic Agents/chemical synthesis , Enzyme Inhibitors/chemical synthesis , Imidazoles/chemical synthesis , Lactams/chemical synthesis , Nitriles/chemical synthesis , Pyrrolidinones/chemical synthesis , Animals , Antineoplastic Agents/chemistry , Antineoplastic Agents/pharmacology , Binding Sites , Binding, Competitive , Biological Availability , Cell Line, Transformed , Dogs , Drug Design , Drug Screening Assays, Antitumor , Enzyme Inhibitors/chemistry , Enzyme Inhibitors/pharmacology , Farnesyltranstransferase , Genes, ras , Imidazoles/chemistry , Imidazoles/pharmacology , Lactams/chemistry , Lactams/pharmacology , Mice , Mice, Transgenic , Models, Molecular , Neoplasms, Experimental/pathology , Nitriles/chemistry , Nitriles/pharmacology , Pyrrolidinones/chemistry , Pyrrolidinones/pharmacology , Radioligand Assay , Stereoisomerism , Structure-Activity RelationshipABSTRACT
A series of amino acid-based linkers was used to investigate the effects of various substituents upon the potency, pharmacokinetic properties, and conformation of macrocyclic farnesyl-protein transferase inhibitors (FTIs). As a result of the studies described herein, highly potent FTIs with improved pharmacokinetic profiles have been identified.
Subject(s)
Alkyl and Aryl Transferases/antagonists & inhibitors , Alkyl and Aryl Transferases/drug effects , Enzyme Inhibitors/administration & dosage , Enzyme Inhibitors/pharmacokinetics , Amino Acids/chemistry , Animals , Cells, Cultured , Dogs , Enzyme Inhibitors/chemical synthesis , Half-Life , Inhibitory Concentration 50 , Metabolic Clearance Rate/physiology , Molecular Conformation , Protein Binding/drug effects , RatsABSTRACT
The previously reported oxytocin antagonist L-371,257 (2) has been modified at its acetylpiperidine terminus to incorporate various pyridine N-oxide groups. This modification has led to the identification of compounds with improved pharmacokinetics and excellent oral bioavailability. The pyridine N-oxide series is exemplified by L-372,662 (30), which possessed good potency in vitro (Ki = 4.1 nM, cloned human oxytocin receptor) and in vivo (intravenous AD50 = 0.71 mg/kg in the rat), excellent oral bioavailability (90% in the rat, 96% in the dog), good aqueous solubility (>8.5 mg/mL at pH 5.2) which should facilitate formulation for iv administration, and excellent selectivity against the human arginine vasopressin receptors. Incorporation of a 5-fluoro substituent on the central benzoyl ring of this class of oxytocin antagonists enhanced in vitro and in vivo potency but was detrimental to the pharmacokinetic profiles of these compounds. Although lipophilic substitution around the pyridine ring of compound 30 gave higher affinity in vitro, such substituents were a metabolic liability and caused shortfalls in vivo. Two approaches to prevent this metabolism, addition of a cyclic constraint and incorporation of trifluoromethyl groups, were examined. The former approach was ineffective because of metabolic hydroxylation on the constrained ring system, whereas the latter showed improvement in plasma pharmacokinetics in some cases.
Subject(s)
Oxazines , Pyridines , Receptors, Oxytocin/antagonists & inhibitors , Administration, Oral , Animals , Biological Availability , Cell Line , Chromatography, High Pressure Liquid , Dogs , Female , Humans , Kidney/cytology , Kidney/embryology , Kidney/metabolism , Liver/metabolism , Male , Mass Spectrometry , Oxazines/chemical synthesis , Oxazines/metabolism , Oxazines/pharmacokinetics , Oxazines/pharmacology , Pregnancy , Pyridines/chemical synthesis , Pyridines/metabolism , Pyridines/pharmacokinetics , Pyridines/pharmacology , Rats , Receptors, Oxytocin/metabolism , Recombinant Proteins/antagonists & inhibitors , Recombinant Proteins/metabolism , Spectrophotometry, Ultraviolet , Uterine Contraction/drug effects , Uterus/drug effects , Uterus/physiologyABSTRACT
To assist in the greatly increasing number of applications of Raman microscopy as a tool for non-intrusive, in situ archaeometric analysis, the Raman spectra of over 60 pigments, both natural and synthetic, known to have been in use before approximately 1850 AD, have been studied by Raman microscopy. Fifty-six pigments have yielded high quality spectra which have been arranged, by colour, into a spectroscopic library for reference purposes. The spectroscopic files may be downloaded from http:/(/)www.ucl.ac.uk/chem/resources/raman/speclib .html.
Subject(s)
Coloring Agents/chemistry , Pigments, Biological/chemistry , Pigments, Biological/history , Spectrum Analysis, Raman/methods , Databases, Factual , History, Ancient , History, Medieval , History, Modern 1601-ABSTRACT
Selenosubtilisin, a semisynthetic enzyme produced by chemical modification of subtilisin's catalytic serine, mimics the antioxidant enzyme glutathione peroxidase, catalyzing the reduction of hydroperoxides by 3-carboxy-4-nitrobenzenethiol. In analogy with the natural peroxidase, a variety of hydroperoxides are accepted as substrates for the semisynthetic enzyme, whereas the dialkyl compound tert-butyl peroxide is not. Kinetic investigations reveal that kmax is dependent upon the nature of the hydroperoxide, indicating that peroxide-mediated oxidation of the enzymic selenolate is at least partially rate-limiting. Experiments with the radical trap 2,6-di-tert-butyl-4-methylphenol suggest that, while the nonenzymic reaction between tert-butyl hydroperoxide and thiol involves free radicals, the same reaction catalyzed by selenosubtilisin does not. The studies described here support the enzyme's proposed ping-pong mechanism and are consistent with previous mechanistic observations.
Subject(s)
Peroxides/metabolism , Subtilisins/metabolism , Catalysis , KineticsABSTRACT
Selenosubtilisin, a semisynthetic selenoenzyme produced by chemical modification of the serine protease subtilisin, acts as a mimic of glutathione peroxidase, catalyzing the reduction of tert-butyl hydroperoxide by 3-carboxy-4-nitrobenzenethiol. To clarify the mechanism of action of this catalyst, detailed kinetic studies have been carried out. Thiol-mediated reduction converts the seleninic acid form of selenosubtilisin (ESeO2H) into a selenenyl sulfide (ESeSAr). Investigations into the reduction of ESeO2H by the aromatic thiol revealed saturation kinetics and were consistent with a significant lowering of the pKa of the seleninic acid in the enzyme active site. While the reduction of ESeO2H was slow compared with a simple model system, the reduced selenoenzyme (ESeSAr) exhibited a much greater peroxidase activity than model compounds. The enzymic selenocysteine residue was shown to be crucial for this activity, and ping-pong kinetics were observed. A catalytic cycle involving interconversion of the ESeSAr, ESeH, and ESeOH forms of the enzyme has been proposed that is consistent with all the available data. The pH-rate profile for the peroxidase activity indicates the involvement of the active site histidine (His64) in the rate-determining step, which these investigations suggest is attack of ArS- on ESeSAr. The results presented here correlated well with crystallographic and spectroscopic data and provide more detailed information about crucial interactions within the active site of selenosubtilisin.
