Transformation of the Ionic X-Ray Contrast Agent Diatrizoate and Related Triiodinated Benzoates by Trametes versicolor

Iodinated X-ray contrast agents are considered to be nondegradable by microorganisms. The decomposition of the ionic X-ray contrast agents Diatrizoate (3,5-di(acetamido)-2,4,6-triiodobenzoic acid) and Iodipamide (3,3′-adipoyl-diimino-di(2,4,6-triiodobenzoic acid) and related triiodinated benzoates (Acetrizoate [3-acetylamino-2,4,6-triiodobenzoic acid] and Aminotrizoate [3-amino-2,4,6-triiodobenzoic acid]) by Trametes versicolor has been investigated. The fungus was able to transform all tested triiodinated benzoates cometabolically. During transformation of these compounds, iodide was released, but deiodination was not complete. T. versicolor liberated traces of ¹⁴CO₂ from uniformly ring-¹⁴C-labeled Diatrizoate (3,5-di(acetamido)-2,4,6-triiodobenzoate). Various extracellular metabolites were detected during transformation of the different substances. In the transformation of Diatrizoate, the three main metabolites were identified as 3,5-di(acetamido)-2,6-diiodobenzoic acid, 3,5-di(acetamido)-2,4-diiodobenzoic acid, and 3,5-di(acetamido)-2-iodobenzoic acid, suggesting reductive deiodinations in steps as initial transformation steps.     

A Transient Study of Formation of Conjugates during TNT Metabolism by Plant Tissues

The formation of TNT-derived conjugates was investigated in hairy root tissue cultures of Catharanthus roseus and in aquatic plant systems of Myriophyllum aquaticum. The temporal profiles of four TNT-derived conjugates, TNT-1, 2A-1, TNT-2 and 4A-1, were determined over 3 to 16-day exposure durations. When axenic C. roseus roots were exposed separately to 2,4,6 trinitrotoluene, 2-amino-4,6-dinitrotoluene and 4-amino-2,6-dinitrotoluene, the array and levels of conjugates varied. Exposure of axenic roots to either 4-amino-2,6-dinitrotoluene or 2-amino-4,6-dinitrotoluene resulted in the formation of only 4A-1 and 2A-1, respectively, and not TNT-1 and TNT-2. However, amendment of previously unexposed roots with TNT produced all four conjugates. The conjugates were preferentially accumulated within the biomass phase of root cultures. Significantly, conjugates TNT-1 and TNT-2 were observed in the biomass phase of intact M. aquaticum plants exposed to TNT. The results clearly indicate the presence of common TNT transformation products in two diverse plants species and tissue type. The distribution of conjugates formed via monoamine derivatives of TNT, however, may be a function of several factors, including the starting xenobiotic type and/or level. Initial bulk rate constants for disappearance of 2,4,6 trinitrotoluene, 2-amino-4,6-dinitrotoluene, and 4-amino-2,6-dinitrotoluene were also determined. Their magnitude followed the order: TNT >> 4-A-2,6-DNT > 2-A-4,6-DNT.     

Two carboxy- and two hydroxymethyl-substituted aristololactams from Aristolochia argentina

Four new aristololactams have been isolated from Aristolochia argentina. The evidence indicates them to be 10-amino-3-hydroxymethyl-2,4-dimethoxyphenanthrene-1-carboxylic acid lactam, 10-amino-3-hydroxymethyl-2,4,6-trimethoxyphenanthrene-1-carboxylic acid lactam, 10-amino-2-hydroxy-4-methoxyphenanthrene-1,3-dicarboxylic acid lactam and 10-amino-2-hydroxy-4,6-dimethoxyphenanthrene-1,3-dicarboxylic acid lactam.     

2,4,6-trinitrotoluene as a trigger of oxidative stress in Fagopyrum tataricum callus cells

Effect of 2,4,6-trinitrotoluene (TNT) on callus cells of Tartar buckwheat (Fagopyrum tataricum (L.) Gaertn.) was accompanied by six-electron reduction of ortho- or para-nitro groups of the xenobiotic with the production of 2-amino-4,6-dinitrotoluene (2-ADNT) and 4-amino-2,6-dinitrotoluene (4-ADNT). It was discovered that the xenobiotic TNT impairs integrity of cell membrane, which apparently results from its one-electron reduction coupled with production of nitro radical-anion and superoxide anion.     

The Synthesis of 2-Amino 7-Substituted Purines

Abstract

The putative antiviral agent, (S)-2-amino-7-(2,3-dihydroxy-propyl) purine (1b), and its achiral analogue, 2-amino-7-(2-hydroxyethyl) purine (2), were synthesized by a procedure involving alkylation at N7 of guanosine followed by deribosylation and deoxygenation. Evidence for the stereochemical integrity of the former preparation was obtained from the X-ray diffraction structure of the novel tricyclic compound, (S)-6H, 7H, 8H-2-amino-7-hydroxy-[1,4] oxazepino [1,2,3-d, elpurine (17, obtained by a similar synthetic sequence. Compound (1a), a regioisomer of the known antiviral agent, (S)-9-(2,3-dihydroxypropyl) adenine ((S)-DHPA), was tested and found to be inactive in tissue culture against herpes virus type-2, rotavirus, poliovirus, and parainfluenza virus.     

Synthesis and Biological Activity of Cyclohexenyl Nucleosides. cis-5-(9H-Purin-9-yl)-3-cyclohexenyl Carbinols and Their 8-Azapurinyl Analogs

Abstract

5-Azido-3-cyclohexenecarboxylic acid was reduced to an aminocyclohexenyl-carbinol which was coupled with either 5-amino-4,6-dichloropyrimidine or 2-amino-4,6-dichloropyrimidine, giving 5-pyrimidinyl-3-cyclohexencarbinols. Condensation with triethylorthoformate or nitrous acid formed the purine and 8-azapurine ring systems, respectively. Anti-HIV-1 and cytotoxicity testing results are also described.     

Effect of benzoannulation on tautomeric preferences of 4,6-di(pyridin-2-yl)cyclohexane-1,3-dione

Density functional theory (DFT) calculations at the B3LYP/6-311+G(d,p) level show that 4,6-di(pyridin-2-yl)cyclohexane-1,3-dione is a labile compound. On the other hand, its dienolimine tautomer (4,6-di(pyridin-2-yl)cyclohaxa-1,3-diene-1,3-diol) seems stable enough to be present in vacuum. Alternatively the equilibriated species are (i) dienolimine and enolimine-enaminone ((6Z)-3-hydroxy-6-(pyridin-2(1H)-ylidene)-4-(pyridine-2-yl)cyclohex-3-enone) or (ii) dienolimine, enolimine-enaminone and dienaminone ((4Z,6Z)-4,6-di(pyridin-2(1H)-ylidene)cyclohexane-1,3-dione). Benzoannulation of the pyridine ring at position 5,6 was found to increase the contribution of the tautomers which contain the enaminone moiety. Energies of the transition states between the stable tautomers were also calculated in order to estimate activation energy of the proton transfer. Values of the geometry based harmonic oscillator model of aromaticity (HOMA) index and Laplacian of the electron density in the hydrogen bond critical point (based on quantum theory of atom in molecules) shows that the enaminone moiety in the tautomers studied are stabilized by stronger intramolecular hydrogen bond than this present in the enolimine moiety.     

Acyclic Nucleotides Related to Clitocine: Synthesis and Anti-HIV Activity

Abstract

The syntheses and antiviral activity of analogues of the anti-HIV agents PMEA, PMEDAP, (R)-PMPA, (R)-PMPDAP are described. In these analogues the adenine moiety is replaced by 4,6-diamino-5-nitro-pyrimidine (the aglycon of clitocine) or 2,4,6-triamino-5-nitro-pyrimidine. The synthesis of similar acyclic phosphonates related to PMEG and (R)-2′-methyl-PMEG is also reported. Some compounds proved to be active as anti-HIV agents.     

Cyclic retro-inverso dipeptides with two aromatic side chains. I. Synthesis.

A series of cyclic retro-inverso dipeptides--2-[(4-hydroxy)benzyl]-5-benzyl-4,6(1H,2H,3H,5H)-pyrimidinedi one (c[mPhe-gTyr]), 2-benzyl-5-[(4-hydroxy)benzyl]-4,6(1H,2H,3H,5H)-pyrimidinedione (c[mTyr-gPhe]), and 2-benzyl-5-amino-5-[(4-hydroxy)benzyl]-4,6(1H,2H,3H,5H)-pyrimidinedione (c[(alpha-amino)mTyr-gPhe])--were synthesized in order to define the minimum structural requirements for binding affinity with opiate receptors and biological activity. Although the first two compounds lack a free amine proposed to be necessary for receptor recognition, the c[mPhe-gTyr] and c[mTyr-gPhe] analogues serve as model molecules in conformational studies of the target analogue, c[(alpha-amino)mTyr-gPhe]. The cis- and trans-c[(alpha-amino)mTyr-gPhe] contain all the functional groups such as the amine and phenolic groups in the tyrosine, and the aromatic group in the phenylalanine, necessary for opiate activity. In addition, the c[(alpha-amino)mTyr-gPhe] analogues possess similar geometries to the Tyr-Pro part of morphiceptin (Tyr-Pro-Phe-Pro-NH2) whose high mu-receptor activity is attributed to conformations with the Tyr-Pro amide bond in a cis conformation because the peptide bonds assume a cis conformation. However, both analogues are inactive in the guinea pig ileum and the mouse vas deferens assays. This may result from wrong orientation of the benzyl group of the gPhe residue with respect to the (alpha-amino)mTyr residue. Conformational studies of these molecules using 1H-nmr spectroscopy and molecular mechanics calculations will be reported in the following paper. Results of conformational analysis should provide information about backbone-side-chain interactions in the retro-inverso peptide chains since all the fundamental structural elements of the retro-inverso peptides are included in these model systems even though the peptide bonds must assume a cis conformation.     

Rapid separation of reduction products of 2,4,6-trinitrotoluene using TLC

Silica gel TLC methods were developed for the separation of 2,4,6-trinitrotoluene (TNT) in mixtures with possible reduction products. The methods employed repeated elutions with simple binary or ternary solvent systems in either one or two dimensional modes. The resolved analytes include TNT, selected amino derivatives (2-amino-4,6-di-nitrotoluene, 4-amino-2,6-dinitrotoluene, 2,4-diamino-6-nitrotoluene) and known hydroxylamino derivatives (2-hydroxyl-amino-4,6-dinitrotoluene, 4-hydroxylamino-2,6-dinitrotoluene and 2,4-dihydroxylamino-6-nitrotoluene).     

Synthesis of the conjugation ready, downstream disaccharide fragment of the O-PS of Vibrio cholerae O:139

The linker-equipped disaccharide, 8-amino-3,6-dioxaoctyl 2,6-dideoxy-2-acetamido-3-O-β-d-galactopyranosyluronate-β-d-glucopyranoside (10), was synthesized in eight steps from acetobromogalactose and ethyl 4,6-O-benzylidene-2-deoxy-2-trichloroacetamido-1-thio-β-d-glucopyranoside. The hydroxyl group present at C-4^II in the last intermediate, 8-azido-3,6-dioxaoctyl 4-O-benzyl-6-bromo-2,6-dideoxy-2-trichloroacetamido-3-O-(benzyl 2,3-di-O-benzyl-β-d-galactopyranosyluronate)-β-d-glucopyranoside (9), is positioned to allow further build-up of the molecule and, eventually, construction of the complete hexasaccharide. Global deprotection (9→10) was done in one step by catalytic hydrogenolysis over palladium-on-charcoal.     

Biosynthesis of vitamin B2: Structure and mechanism of riboflavin synthase

The biosynthesis of one riboflavin molecule requires one molecule of GTP and two molecules of ribulose 5-phosphate as substrates. GTP is hydrolytically opened, converted into 5-amino-6-ribitylamino-2,4(1H,3H)-pyrimidinedione by a sequence of deamination, side chain reduction and dephosphorylation. Condensation with 3,4-dihydroxy-2-butanone 4-phosphate obtained from ribulose 5-phosphate leads to 6,7-dimethyl-8-ribityllumazine. The final step in the biosynthesis of the vitamin involves the dismutation of 6,7-dimethyl-8-ribityllumazine catalyzed by riboflavin synthase. The mechanistically unusual reaction involves the transfer of a four-carbon fragment between two identical substrate molecules. The second product, 5-amino-6-ribitylamino-2,4(1H,3H)-pyrimidinedione, is recycled in the biosynthetic pathway by 6,7-dimethyl-8-ribityllumazine synthase. This article will review structures and reaction mechanisms of riboflavin synthases and related proteins up to 2007 and 122 references are cited.     

Synthesis of 2-amino-2-deoxy- and 3-amino-3-deoxy-α-d-mannopyranosyl α-d-mannopyranoside by sequential osmylations of a dienic disaccharide

Partial oxyamination of 4,6-di-O-acetyl-2,3-dideoxy-α-d-erythro-hex-2-enopyranosyl 4,6-di-O-acetyl-2,3-dideoxy-α-d-erythro-hex-2-enopyranoside with chloramine-T and osmium tetraoxide gave 4,6-di-O-acetyl-2-deoxy-2-(p-toluene-sulfonamido)-α-d-mannopyranosyl 4,6-di-O-acetyl-2,3-dideoxy-α-d-erythro-hex-2-enopyranoside and its 3-deoxy-3-(p-toluenesulfonamido) regioisomer, each in 18–19% isolated yield. Osmium tetraoxide-catalyzed cis-hydroxylation of the remaining alkenic residue in these products led in high yields to the corresponding triols having the α-d-manno, α-d-manno configuration. These were N-desulfonylated (and simultaneously O-deacetylated) by the action of sodium in liquid ammonia to furnish 2-amino-2-deoxy-α-d-mannopyranosyl α-d-mannopyranoside and 3-amino-3-deoxy-α-d-mannopyranosyl α-d-mannopyranoside as new, trehalose-type amino sugars.     

Cyclic retro-inverso dipeptides with two aromatic side chains. II. Conformational analysis.

The conformations of cis and trans cyclic retro-inverso dipeptides--2-[(4-hydroxy)benzyl]-5-benzyl-4,6(1H,2H,3H,5H)-pyrimidinedi one (c[mTyr-gPhe]), and 2-benzyl-5-amino-5-[(4-hydroxy)benzyl]-4,6(1H,2H,3H,5H)-pyrimidinedione (c[mTyr-gPhe]), and 2-benzyl-5-amino-5-[(4-hydroxy)benzyl]-4,6(1H,2H,3H,5H)-pyrimidinedione (c[(alpha-amino)mTyr-gPhe])--and the parent cyclic dipeptides--c[tyrosyl-phenylalanine] (cis-c[L-Tyr-L-Phe]) and c[tyrosyl-D-phenylalanine] (trans-c[L-Tyr-D-Phe])--were studied by using 1H-nmr spectroscopy and semiempirical energy calculations. In the cis compounds of all the cyclic retro-inverso and parent dipeptides, the most stable conformer has both aromatic side chains sharing the space over the backbone ring in a "face-to-face" fashion. All the trans compounds predominantly assume a "sandwich" conformation in which the two aromatic rings are folded back over the backbone ring on opposite sides. However, different conformational preferences were observed for the backbones between the retro-inverso and parent cyclic dipeptides. The parent cyclic dipeptide trans-c[L-Tyr-D-Phe] adopts two types of boat structures with different side-chain orientations in almost equal amounts: one with the Tyr side chain in a pseudoaxial position and the Phe side chain in a pseudoequatorial position, the other with the Tyr side chain in a pseudoequatorial position and the Phe side chain in a pseudoaxial position. On the other hand, the cyclic retro-inverso dipeptides trans-c[mPhe-gTyr] and trans c[mTyr-gPhe] assume only one type of boat structure in which the malonyl side chain is in a pseudoequatorial and the gem-diamino side chain is in a pseudoaxial position. In addition to the preferred conformations, the conformational energies of the C alpha--C beta bonds in the malonyl and gem-diamino residues were estimated from the temperature variation of vicinal 1H--1H coupling constants for the H--C alpha--C beta--H groupings observed for the trans isomers of cyclic retro-inverso dipeptides. The energies were evaluated to be 1.1 and 1.8 kcal mol-1 for the malonyl and gem-diamino residues, respectively. Applying these energies to the parent cyclic dipeptide trans-c[L-Tyr-D-Phe], the observed fractions of three side-chain conformations are reasonably reproduced. The conformational energies as well as conformational properties of the molecules estimated in this investigation may be useful to refine force constants for both parent and retro-inverso peptides with aromatic side chains.     

NAD(P)H:Flavin Mononucleotide Oxidoreductase Inactivation during 2,4,6-Trinitrotoluene Reduction

Bacteria readily transform 2,4,6-trinitrotoluene (TNT), a contaminant frequently found at military bases and munitions production facilities, by reduction of the nitro group substituents. In this work, the kinetics of nitroreduction were investigated by using a model nitroreductase, NAD(P)H:flavin mononucleotide (FMN) oxidoreductase. Under mediation by NAD(P)H:FMN oxidoreductase, TNT rapidly reacted with NADH to form 2-hydroxylamino-4,6-dinitrotoluene and 4-hydroxylamino-2,6-dinitrotoluene, whereas 2-amino-4,6-dinitrotoluene and 4-amino-2,6-dinitrotoluene were not produced. Progressive loss of activity was observed during TNT reduction, indicating inactivation of the enzyme during transformation. It is likely that a nitrosodinitrotoluene intermediate reacted with the NAD(P)H:FMN oxidoreductase, leading to enzyme inactivation. A half-maximum constant with respect to NADH, K_N, of 394 μM was measured, indicating possible NADH limitation under typical cellular conditions. A mathematical model that describes the inactivation process and NADH limitation provided a good fit to TNT reduction profiles. This work represents the first step in developing a comprehensive enzyme level understanding of nitroarene biotransformation.     

Structure guided inhibitor designing of CDK2 and discovery of potential leads against cancer

On the basis of stereo specific information obtained from crystal structures of CDK2, indole and chromene analogues were designed by suitably substituting the pharmacophores on their moiety and docked with target protein for calculating binding affinities. The binding affinities are represented in glide score. (5E)-5-[(1-methyl-1H-indol-3-yl)methylidene]-2,4,6-trioxotetrahydro-2H-pyrimidin-1-ide (I₁), (5E)-5-(1H-indol-3-ylmethylidene)-2,4,6-trioxotetrahydro-2H-pyrimidin-1-ide (I₂) and 2-amino-4-(4-methyl phenyl)-5-oxo-5,6,7,8-tetrahydro-4H-chromene-3-carbonitrile (C₉) were selected for synthesis and biological testing based on vital interactions. (5E)-5-(1H-indol-3-ylmethylidene)-2,4,6-trioxotetrahydro-2H-pyrimidin-1-ide(I₂) and 2-amino-4-(4-methyl phenyl)-5-oxo-5,6,7,8-tetrahydro-4H-chromene-3-carbonitrile (C₉) were proved to be active against MCF-7 and HeLa cell lines.     

Efficient synthesis of 17-acetyl-13-(p-bromophenyl)-3-methoxy-11,11-bis(methoxycarbonyl)gona-1,3,5(10)-trienes

We described an efficient synthesis of (8β,9β,14β)-17β-acetyl-13β-p-bromophenyl-11,11-di(methoxycarbonyl)-3-methoxygona-1,3,5(10)-triene, (8β,9α,14β)-17β-acetyl-13β-p-bromophenyl-11,11-di(methoxycarbonyl)-3-methoxygona-1,3,5(10)-triene, (8β,9β,14β)-13 β-p-bromophenyl-11,11-di(methoxycarbonyl)-17β-(2-hydroxyethyl)-3-methoxygona-1,3,5(10)-triene, and (8β,9β,14β)-13β-p-bromophenyl-11,11-di(methoxycarbonyl)-17β-(2-oxoxyethyl)-3-methoxygona-1,3,5(10)-triene in five or six steps from 1-iodo-4-methoxybenzocyclobutene and readily available materials.     

The Biosynthesis and Metabolism of Acarbose in Actinoplanes sp. SE 50/110: A Progress Report

Abstract

The α-glucosidase inhibitor acarbose produced by Actinoplanes sp. SE50/110 is a pseudotetrasaccharide, which consists of an unsaturated cyclitol (carba-sugar), 4-amino-4,6-dideoxyglucose and maltose. The cyclitol (valienol) and the 4-amino-4,6-dideoxyglucose are linked via an N-glycosidic (imino) bond, forming the so-called acarviosyl moiety, which is primarily responsible for the inhibitory effect on α-glucosidases. The gene cluster encoding the biosynthetic genes for the synthesis of acarbose (acb-genes) was sequenced and 25 open reading frames belonging to the acb-gene cluster were identified. Based on the analysis of the enzymes encoded by the acb-cluster, the biosynthesis and ecological role of acarbose is described. The gene cluster includes genes which encode: proteins for the synthesis of the cyclitol; the enzymes for the synthesis of dTDP-4-amino-4,6-dideoxyglucose; glycosyltransferases for the condensation reactions; ATP-dependent exporters and importers; extracellular starch degrading enzymes; and intracellular acarbose modifying enzymes. Acarbose has a dual role for the producer: it inhibits α-glucosidic enzymes of competitors and functions as a carbophor for the uptake of glucose or starch molecules.     

Fate and Transport of 2,4,6-Trinitrotoluene in Loams at a Former Explosives Factory

Natural attenuation processes affecting 2,4,6-trinitrotoluene (TNT) were determined within loams for two study areas at the former Explosives Factory Maribyrnong, Australia. TNT fate and transport was investigated through spectrophotometric/High Performance Liquid Chromatography (HPLC) analyses of soil and groundwater, adsorption and microcosm testwork. A five tonne crystalline TNT source zone delineated within near surface soils at the base of a TNT process waste lagoon was found to be supplying aqueous TNT loading (7 ppm) to subsurface soils and groundwater. The resultant plume was localized within the loam aquitard due to a combination of natural attenuation processes and hydrogeological constraints, including low hydraulic conductivity and upward hydraulic gradients. Freundlich described sorptive partitioning was the main TNT sink (K_F = 29 mL/g), while transformation rates were moderate (1.01 × 10^-4 h^-1) under the aerobic conditions. Increasing 2-amino-4,6-dinitrotoluene predominance over 4-amino-2,6-dinitrotoluene was discovered with depth (in situ) and time (microcosms). Simplified dissolution rate calculations indicate that without mitigation of the TNT source, contaminant persistence within the vadose zone may approach 2000 years, while ATRANS20 simulations demonstrate that the TNT plume propagates very slowly along the flow path within the aquitard.     

NOVEL NUCLEOSIDE TRIPHOSPHATE ANALOGS FOR THE ENZYMATIC LABELING OF NUCLEIC ACIDS

We have evaluated several novel nucleotide analogs suitable for enzymatic labeling of nucleic acid targets for a variety of array-based assays. Two new reagents in particular, a C4-labeled 1-(2′,3′-dideoxy-β-D-ribofuranosyl) imid- azole-4-carboxamide 5′-triphosphate 5 and an N1-labeled 5-(β-D- ribofuranosyl)-2,4(1H,3H)-pyrimidinedione 5′-triphosphate 3, were found to be excellent substrates for labeling with terminal deoxynucleotidyl transferase and T7 RNA polymerase, respectively.