Dragic Vukomanovic

Heme Oxygenase Inhibition by 2‐Oxy‐substituted 1‐Azolyl‐4‐phenylbutanes: Effect of Variation of the Azole Moiety. X‐Ray Crystal Structure of Human Heme Oxygenase‐1 in Complex with 4‐Phenyl‐1‐(1H‐1,2,4‐triazol‐1‐yl)‐2‐butanone†

A series of 1‐azolyl‐4‐phenyl‐2‐butanones was designed and synthesized for the inhibition of heme oxygenases (heme oxygenase‐1 and heme oxygenase‐2). The replacement of imidazole by other azoles led to the discovery of novel 1H‐1,2,4‐triazole‐ and 1H‐tetrazole‐based inhibitors equipotent to a lead imidazole‐based inhibitor. The inhibitors featuring 2H‐tetrazole or 1H‐1,2,3‐triazole as the pharmacophore were less potent. Monosubstitution at position 2 or 4(5), or identical disubstitution at positions 4 and 5 of imidazole by a variety of electron‐withdrawing or electron‐donating, small or bulky groups, as well as the replacement of the traditional imidazole pharmacophore by an array of 3‐ or 5‐substituted triazoles, identically 3,5‐disubstituted triazoles, 5‐substituted‐1H‐ and 5‐substituted‐2H‐tetrazoles proved to be detrimental to the inhibition of HO, with a few exceptions. The azole‐dioxolanes and the azole‐alcohols derived from the active azole‐ketones were synthesized also, but these inhibitors were less active than the corresponding imidazole‐based analogs. The first reported X‐ray crystal structure of human heme oxygenase‐1 in complex with a 1,2,4‐triazole‐based inhibitor, namely 4‐phenyl‐1‐(1H‐1,2,4‐triazol‐1‐yl)‐2‐butanone, was also determined. The inhibitor binds to the human heme oxygenase‐1 distal pocket through the coordination of heme iron by the N 4 in the triazole moiety, whereas the phenyl group is stabilized by hydrophobic interactions from residues within the binding pocket.

COLLISIONAL DISSOCIATION STUDIES OF CU2+(H2O)N USING ELECTROSPRAY IONIZATION MASS SPECTROMETRY

Abstract Contrary to an earlier report [A.T. Blades, P. Jayaweera, M.G. Ikonomou, P. Kebarle, J. Chem. Phys. 92 (1990) 5900], hydrated cupric ions Cu2+(H2O)n (n = 4–14) are readily produced in the gas phase by electrospray ionization and possess sufficient intensities for collision-assisted dissociation studies. Daughter ions, Cu2+(H2O)x, with x as low as 2 are observed to be stable. Charge reduction yielding CuOH(H2O)n−y+ is observed but declines in importance with increase in the size of the hydration shell. Methanol can exchange with some of the water molecules in Cu2+(H2O)n.

Heme Oxygenase Inhibition by 1‐Aryl‐2‐(1H‐imidazol‐1‐yl/1H‐1,2,4‐triazol‐1‐yl)ethanones and Their Derivatives

Previous studies by our research group have been concerned with the design of selective inhibitors of heme oxygenases (HO‐1 and HO‐2). The majority of these were based on a four‐carbon linkage of an azole, usually an imidazole, and an aromatic moiety. In the present study, we designed and synthesized a series of inhibition candidates containing a shorter linkage between these groups, specifically, a series of 1‐aryl‐2‐(1H‐imidazol‐1‐yl/1H‐1,2,4‐triazol‐1‐yl)ethanones and their derivatives. As regards HO‐1 inhibition, the aromatic moieties yielding best results were found to be halogen‐substituted residues such as 3‐bromophenyl, 4‐bromophenyl, and 3,4‐dichlorophenyl, or hydrocarbon residues such as 2‐naphthyl, 4‐biphenyl, 4‐benzylphenyl, and 4‐(2‐phenethyl)phenyl. Among the imidazole‐ketones, five (36–39, and 44) were found to be very potent (IC50<5 μM) toward both isozymes. Relative to the imidazole‐ketones, the series of corresponding triazole‐ketones showed four compounds (54, 55, 61, and 62) having a selectivity index >50 in favor of HO‐1. In the case of the azole‐dioxolanes, two of them (80 and 85), each possessing a 2‐naphthyl moiety, were found to be particularly potent and selective HO‐1 inhibitors. Three non‐carbonyl analogues (87, 89, and 91) of 1‐(4‐chlorophenyl)‐2‐(1H‐imidazol‐1‐yl)ethanone were found to be good inhibitors of HO‐1. For the first time in our studies, two azole‐based inhibitors (37 and 39) were found to exhibit a modest selectivity index in favor of HO‐2. The present study has revealed additional candidates based on inhibition of heme oxygenases for potentially useful pharmacological and therapeutic applications.

Structural insights into human heme oxygenase-1 inhibition by potent and selective azole-based compounds

The development of heme oxygenase (HO) inhibitors, especially those that are isozyme-selective, promises powerful pharmacological tools to elucidate the regulatory characteristics of the HO system. It is already known that HO has cytoprotective properties and may play a role in several disease states, making it an enticing therapeutic target. Traditionally, the metalloporphyrins have been used as competitive HO inhibitors owing to their structural similarity with the substrate, heme. However, given hemes important role in several other proteins (e.g. cytochromes P450, nitric oxide synthase), non-selectivity is an unfortunate side-effect. Reports that azalanstat and other non-porphyrin molecules inhibited HO led to a multi-faceted effort to develop novel compounds as potent, selective inhibitors of HO. This resulted in the creation of non-competitive inhibitors with selectivity for HO, including a subset with isozyme selectivity for HO-1. Using X-ray crystallography, the structures of several complexes of HO-1 with novel inhibitors have been elucidated, which provided insightful information regarding the salient features required for inhibitor binding. This included the structural basis for non-competitive inhibition, flexibility and adaptability of the inhibitor binding pocket, and multiple, potential interaction subsites, all of which can be exploited in future drug-design strategies.

Voltammetric Reduction of Nickel and Cobalt Dimethylglyoximate

The determination of cobalt and nickel in aqueous solutions by stripping voltammetry after adsorptive preconcentration is an established procedure. The method is highly sensitive, but there is some controversy concerning the reasons for the excellent sensitivity. Using a variety of voltammetric techniques, we have determined that the reduction of nickel dimethylglyoximate in an ammonia buffer is consistent with an overall process involving 16 or possibly 18 electrons. This hypothesis is confirmed by independently measuring the total quantity of metal adsorptively deposited on the mercury electrode and comparing the amount with the quantity of electricity required for its reduction.

Heme oxygenase inhibition by α-(1H-imidazol-1-yl)-ω-phenylalkanes: effect of introduction of heteroatoms in the alkyl linker.

Several α‐(1H‐imidazol‐1‐yl)‐ω‐phenylalkanes were synthesized and evaluated as novel inhibitors of heme oxygenase (HO). These compounds were found to be potent and selective for the stress‐induced isozyme HO‐1, showing mostly weak activity toward the constitutive isozyme HO‐2. The introduction of an oxygen atom in the alkyl linker produced analogues with decreased potency toward HO‐1, whereas the presence of a sulfur atom in the linker gave rise to analogues with greater potency toward HO‐1 than the carbon‐containing analogues. The most potent compounds studied contained a five‐atom linker between the imidazolyl and phenyl moieties, whereas the most HO‐1‐selective compounds contained a four‐atom linker between these groups. The compounds with a five‐atom linker containing a heteroatom (O or S) were found to be the most potent inhibitors of HO‐2; 1‐(N‐benzylamino)‐3‐(1H‐imidazol‐1‐yl)propane dihydrochloride, with a nitrogen atom in the linker, was found to be inactive.

New methods for trace titanium determination by adsorptive preconcentration voltammetry with pyrocatechol violet

New sensitive stripping voltammetric procedures for trace measurements of titanium in various samples are reported. The first method is based on the interfacial accumulation of the titanium-pyrocatechol violet complex onto a hanging mercury drop electrode, followed by reduction of the adsorbed complex. The limit of detection is 0.55 nmol/L titanium after a 30 s collection with a stirred solution at pH 4.9. The procedure is extremely selective with respect to other metals and has been applied in analyzing various samples. Based on this, a catalytic method involving the chlorate ion was developed and the sensitivity was enhanced by more than an order of magnitude. In this way, analysis for Ti in aqueous solutions at the picomolar (part per trillion) level is possible.

Selective inhibition of heme oxygenase-2 activity by analogs of 1-(4-chlorobenzyl)-2-(pyrrolidin-1-ylmethyl)-1H-benzimidazole (clemizole): Exploration of the effects of substituents at the N-1 position

Several analogs based on the lead structure of 1-(4-chlorobenzyl)-2-(pyrrolidin-1-ylmethyl)-1H-benzimidazole (clemizole) were synthesized and evaluated as novel inhibitors of heme oxygenase (HO). Many of the compounds were found to be potent and highly selective for the HO-2 isozyme (constitutive), and had substantially less inhibitory activity on the HO-1 isozyme (inducible). The compounds represent the first report of highly potent and selective inhibitors of HO-2 activity, and complement our suite of selective HO-1 inhibitors. The study has revealed many candidates based on the inhibition of heme oxygenases for potentially useful pharmacological and therapeutic applications.

Voltammetric determination of vanadium with adsorptive preconcentration of the pyrocatechol violet complex

A sensitive stripping voltammetric procedure for trace measurements of vanadium in aqueous samples is reported. The method is based on the interfacial accumulation of the vanadium-pyrocatechol complex onto the hanging mercury drop electrode, followed by reduction of the adsorbed complex. The limit of detection is 0.1 nM vanadium after a 3 min collection with a stirred solution at pH 4.7. The procedure is selective with respect to other metals and has been applied in analysing various samples.

X-ray crystal structure of human heme oxygenase-1 with (2R,4S)-2-[2-(4-chlorophenyl)ethyl]-2-[(1H-imidazol-1-yl)methyl]-4[((5-trifluoromethylpyridin-2-yl)thio)methyl]-1,3-dioxolane: a novel, inducible binding mode.

The crystal structure of human heme oxygenase-1 (HO-1) in complex with (2R,4S)-2-[2-(4-chlorophenyl)ethyl]-2-[(1H-imidazol-1-yl)methyl]-4[((5-trifluoromethylpyridin-2-yl)thio)methyl]-1,3-dioxolane (4) reveals a novel, inducible binding mode. Inhibitor 4 coordinates the heme iron, with its chlorophenyl group bound in a distal hydrophobic pocket, as seen in previous structures. However, accommodation of the 5-trifluoromethylpyridin-2-yl group requires a significant shift in the proximal helix, inducing the formation of a hydrophobic pocket. This is the first example of an induced binding pocket observed in HO-1.