μ-1,2,4,5-Tetrazine-N:N-bis(pentaammineruthenium) tetracation: Synthesis and X-ray structure

The 2:1 reaction of [Ru(H₂O)₂(NH₃)₅]²⁺ with 1,2,4,5-tetrazine (tz) gives rise to the formation of the dinuclear complex ion [{Ru(NH₃)₅}₂(μ-tz-N¹:N⁴)]⁴⁺. Its tetraphenylborate and hexafluoro-phosphate salts have been fully characterized; the X-ray structure of the former has also been determined.     

Alkaloids of Papaver bracteatum: 14-β-hydroxycodeinone, 14-β-hydroxycodeine and N-methylcorydaldine

Three new alkaloids have been identified from Papaver bracteatum, 14-β-hydroxycodeinone, 14-β-hydroxycodeine and N-methylcorydaldine. The presence of alpinigenine was also confirmed.     

Progress in antischistosomal N,N′-diaryl urea SAR

N,N′-Diaryl ureas have recently emerged as a new antischistosomal chemotype. We now describe physicochemical profiling, in vitro ADME, plasma exposure, and ex vivo and in vivo activities against Schistosoma mansoni for twenty new N,N′-diaryl ureas designed primarily to increase aqueous solubility, but also to maximize structural diversity. Replacement of one of the 4-fluoro-3-trifluoromethylphenyl substructures of lead N,N′-diaryl urea 1 with azaheterocycles and benzoic acids, benzamides, or benzonitriles decreased lipophilicity, and in most cases, increased aqueous solubility. There was no clear relationship between lipophilicity and metabolic stability, although all compounds with 3-trifluoromethyl-4-pyridyl substructures were metabolically stable. N,N′-diaryl ureas containing 4-fluoro-3-trifluoromethylphenyl, 3-trifluoromethyl-4-pyridyl, 2,2-difluorobenzodioxole, or 4-benzonitrile substructures had high activity against ex vivo S. mansoni and relatively low cytotoxicity. N,N-diaryl ureas with 3-trifluoromethyl-4-pyridyl and 2,2-difluorobenzodioxole substructures had the highest exposures whereas those with 4-fluoro-3-trifluoromethylphenyl substructures had the best in vivo antischistosomal activities. There was no direct correlation between compound exposure and in vivo activity.     

Enhancement of the mutagenicities of N-methyl-N′-nitro-N-nitrosoguanidine and N-methyl-N-nitrosourea by glucose

The mutagenicity of N-methyl-N′-nitro-N-nitrosoguanidine to Salmonella typhimurium hisG46 was enhanced by pre-incubating the chemical with bacteria in sodium phosphate buffer. Addition of glucose (to 15 mM) to the pre-incubation mixture further enhanced the mutagenicity. Pre-incubation with glucose also increased the mutagenicity of N-methyl-N-nitrosourea. Fructose, galactose, pyruvate and succinate also enhanced the mutagenicity of N-methyl-N′-nitro-N-nitrosoguanidine. The effect of glucose was observed with S. typhimurium strains hisG46, TA1975, TA1950, TA1535 and TA100.     

1,3-Bis(α-aminoisopropyl)benzene, meta-C6H4(CMe2NH2)2: An N,N-bridging and N,C,N-cyclometalating ligand

Saponification of the bis(carbamic acid ester) 1,3-C₆H₄(CMe₂NHCO₂Me)₂ (1), made by the addition of methanol to commercial 1,3-C₆H₄(CMe₂NCO)₂, yielded the meta-phenylene-based bis(tertiary carbinamine) 1,3-C₆H₄(CMe₂NH₂)₂ (2). Dinuclear [{(η⁴-1,5-C₈H₁₂)RhCl}₂{μ-1,3-C₆H₄(CMe₂NH₂)₂}] (3) resulted from the action of 2 on [{(η⁴-1,5-C₈H₁₂)Rh(μ-Cl)}₂] in toluene. Combination of 2 with PdCl₂ or K₂[PdCl₄] gave the dipalladium macrocycle trans,trans-[{μ-1,3-C₆H₄(CMe₂NH₂)₂}₂(PdCl₂)₂] (4) along with cyclometalated [{2,6-C₆H₃(CMe₂NH₂)₂-κN,κC¹,κN′}PdCl] (5). Substitution of PEt₃ for the labile chlorido ligand of 5 afforded [{2,6-C₆H₃(CMe₂NH₂)₂-κN,κC¹, κN′}Pd(PEt₃)]Cl (6). The crystal structures of the following compounds were determined: bis(carbamic acid ester) 1, ligand 2 as its bis(trifluoroacetate) salt [1,3-C₆H₄(CMe₂NH₃)₂](O₂CCF₃)₂, 2 · (HAc_f)₂, complexes 3 and 6, as well as 1,3-C₆H₄(CMe₂OH)₂ (the diol analogue of 2).     

N-(ϱ-coumaryl)-tryptamine and N-ferulyl tryptamine in kernels of Zea mays

N-(?-coumaryl)tryptamine and N-ferulyltryptamine were isolated from aqueous acetone extracts of ground kernels of Zea mays by successive column chromatography on partially sulfonated styrenedivinylbenzene copolymer resin, lipophilic Sephadex and preparative TLC. Identification of these compounds was made by GCMS of their trimethylsilyl derivatives and the trimethylsilyl derivatives of their acid hydrolysis products.     

Fluorescent cytokinins: Stretched-out analogs of N6-benzyladenine and N6-(Δ2-isopentenyl) adenine

We have synthesized and compared the cytokinin activities in the tobacco bioassay of a series of benzologs of 6-(3-methyl-2-butenylamino)purine (N⁶-(Δ²-isopentenyl)adenine) (1a) and 6-benzylaminopurine (N⁶-benzyl-adenine) (1c). The linear benzo analogs 8-(3-methyl-2-butenylamino)imidazo[4,5-g]quinazoline (2b) and 8-benzyla-minoimidazo[4,5-g]quinazoline (2c) are active, while 9-(3-methyl-2-butenylamino)imidazo[4,5-f]quinazoline (3b) and 6-(3-methyl-2-butenylamino)imidazo[4,5-h]quinazoline (4b) are slightly active and 9-benzylaminoimidazo[4,5-f]-quinazoline (3c) and 6-benzylaminoimidazo[4,5-h]quinazoline (4c) are inactive. Compounds 2b and 2c represent the first examples of active cytokinins containing a tri-heterocyclic moiety. The above series of compounds demonstrates structural factors that affect cytokinin activity. These compounds also have interesting fluorescence properties which could render them useful as probes to study the mechanism of cytokinin action.     

The effect of hydrogen bonding in two crystal modifications of aquabis(N,N-dimethylglycinato-κN,κO)copper(II): Experimental and theoretical study

From the crystals of trans aquabis(N,N-dimethylglycinato-κN,κO)copper(II) dihydrate (compound 1, space group P2₁2₁2₁) novel crystal structure of trans aquabis(N,N-dimethylglycinato-κN,κO)copper(II) (compound 2, space group Pbca) was obtained and analysed by X-ray diffraction. In the crystal structure 1, the O-H?O hydrogen bonds form three-dimensional network. In the crystal structure 2, two-dimensional layers stacking to each other are formed, with non-polar N,N-dimethyl groups placed on the opposite sides of the layers, and with the polar part in the middle forming CO?O-H and C-H?O hydrogen bonds. Different hydrogen bonding patterns in 1 and 2 do not pronouncedly affect molecular geometry of the title compound. Molecular mechanics force field suited for studying the properties of bis(amino acidato)copper(II) complexes in the solid state can follow the differences between the experimental molecular structures in the two diverse crystalline surroundings. To make possible direct comparison between crystal lattices, the force field was applied to predict unit cell packing of supposed anhydrous bis(N,N-dimethylglycinato)copper(II) in space group Pbca. Relative intermolecular energies of hypothetic anhydrous crystal and simulated 1 and 2 crystals are discussed. On the basis of experimental and theoretical results we conclude that the main effect of two water molecules of crystallisation in 1 is to stabilise the crystal packing via hydrogen bonding, whilst similar pyramidal copper(II) coordination geometry in 1 and 2 is due to axially coordinated water molecule and its intermolecular interactions.     

Phosphorylase-catalyzed N-formyl-α-glucosaminylation of maltooligosaccharides

This paper describes the phosphorylase-catalyzed enzymatic N-formyl-α-glucosaminylation of maltooligosaccharides for direct incorporation of 2-deoxy-2-formamido-α-d-glucopyranose units into maltooligosaccharides. When the reaction of 2-deoxy-2-formamido-α-d-glucopyranose-1-phosphate (GlcNF-1-P) as the glycosyl donor and maltotetraose as a glycosyl acceptor was performed in the presence of phosphorylase, the N-formyl-α-d-glucosaminylated pentasaccharide was produced, as confirmed by MALDI-TOF MS. Furthermore, the glucoamylase-catalyzed reaction of the crude products supported that the 2-deoxy-2-formamido-α-d-glucopyranoside unit was positioned at the non-reducing end of the pentasaccharide. The pentasaccharide was isolated from the crude products and its structure was further determined by the ¹H NMR analysis. On the other hand, when the phosphorylase-catalyzed reactions of maltotriose and maltopentaose using GlcNF-1-P were conducted, no N-formyl-α-glucosaminylation took place in the former system, whereas the latter system gave N-formyl-α-d-glucosaminylated oligosaccharides with various degrees of polymerization. These results could be explained by the recognition behavior of phosphorylase toward maltooligosaccharides.     

Synthesis, X-ray crystal structure and magnetic study of the 1D {[Cu2(N,N,N′,N′-tetramethyl-ethylenediamine)2(μ-1,5-dca)2(dca)2]}n complex

Reaction of Cu(NO₃)₂ · 3H₂O, N,N,N′,N′-tetramethyl-ethylenediamine (L) and sodium dicyanamide (Nadca) in aqueous medium yields a complex the {[Cu₂L₂(μ-1,5-dca)₂(dca)₂]}_n complex, 1. Single crystal X-ray analysis reveals that complex 1 has a 1D infinite chain structure in which copper(II) ions are bridged by single dicyanamide anions in an end-to-end fashion. The coordination environment around copper(II) is distorted square pyramidal. Two among the four coordination sites of the basal plane are occupied by the nitrogen atoms of the diamine and two remaining sites are occupied by the terminal nitrogen atom of a bridging and of a monodentate dca anions. The fifth coordination site (apical) is occupied by a nitrogen atom from a bridging dca anion of an adjacent CuL(dca)₂ moiety, yielding the [Cu₂L₂(μ-1,5-dca)₂(dca)₂] dinuclear unit. Dimeric units are connected to each other by single μ-1,5-dicyanamido group to form infinite 1D chains which propagate parallel to the crystallographic c-axis. The variable temperature magnetic susceptibility measurements evidenced weakly antiferromagnetic interactions (J = −0.26 cm⁻¹) in {[Cu₂L₂(μ-1,5-dca)₂(dca)₂]}_n, 1.     

A homologous series of apoptosis-inducing N‑acylserinols: Thermotropic phase behavior,interaction with cholesterol and characterization of cationic N‑myristoylserinol-cholesterol-CTAB niosomes

N?Acylserinols (NASOHs) exhibit anti-cancer activity by elevating ceramide levels, and/or by activating proapoptotic effectors. In the present work we investigated the thermotropic phase behavior and supramolecular organization of a homologous series of NASOHs (number of C-atoms in the acyl chain, n?=?8–18), and the interaction of N-myristoylserinol (NMSOH) with cholesterol, and characterized cationic niosomes made up of NMSOH, cholesterol and cetyltrimethylammonium bromide (CTAB). Differential scanning calorimetric studies revealed that NASOHs exhibit a major chain-melting phase transition in both dry and hydrated states. The thermodynamic parameters, transition enthalpy and entropy show linear dependence on the acyl chain length in the dry state, but exhibit odd-even alternation in the hydrated state. Powder X-ray diffraction studies revealed that NASOHs adopt a tilted bilayer structure, wherein the bilayer repeat distances (d-spacings) also showed odd-even alteration, with even-chainlength compounds exhibiting slightly higher d-spacings. Studies on the interaction between NMSOH and cholesterol revealed that both lipids mix well with up to 55?mol% cholesterol, whereas phase separation was observed at higher cholesterol content. The transition enthalpy corresponding to the NMSOH-cholesterol complex increases up to 55?mol% cholesterol and decreases at higher cholesterol content. Presence of the cationic surfactant CTAB affects the phase behavior, fluidity and size of the NMSOH-cholesterol (45,55, mol/mol) niosomes, with unilamellar vesicles of about 85 (±20) nm in diameter being obtained at 10?mol% CTAB. These results provide a thermodynamic and structural basis for further investigations on these cationic niosomes towards their use in drug delivery applications, especially for anticancer drugs.     

N′-isopropylnornicotine: Its formation from nicotine in aged leaves of Nicotiana tabacum

An aqueous solution of nicotine-[2′-¹⁴C] was painted on the leaves of 4-month-old tobacco plants (Nicotiana tabacum) which were harvested 3 weeks later. This tracer was similarly applied to excised tobacco leaves which were allowed to dry in air for 4 weeks. The alkaloids, were extracted with the addition of N′-isopropylnornicotine, a compound which has been previously isolated from air-cured tobacco. Radioactive nicotine and nornicotine were isolated from the intact plants with only minute activity in the N′-isopropylnornicotine. All three of these alkaloids were radioactive from the air-cured leaves, and degradation of the labelled N'-isopropylnornicotine indicated that all the activity was located at the C-2′ position. A higher level of activity was found in N′-isopropylnornicotine which was obtained from excised leaves which were fed the nicotine- [2′- ¹⁴C] in aqueous acetone, and were treated on subsequent days with aqueous acetone. These results are consistent with the hypothesis that N′-isopropylnornicotine is produced in the curing of tobacco leaves by reaction of nornicotine (formed by the demethylation of nicotine) with acetoacetate, followed by decarboxylation and reduction. The ¹³C NMR chemical shifts of the methyl groups of N′-isopropylnornicotine and related 1-isopropylpyrrolidines which have chirality at the α-position of the pyrrolidine ring, are significantly different (up to 7.5 ppm).     

An ectotherm homologue of human predicted gene NAT16 encodes histidine N-acetyltransferase responsible for Nα-acetylhistidine synthesis

Background

Nα-Acetylhistidine (NAH) is present in very high concentrations exclusively in the brain and lens of ectothermic vertebrates, including ray-finned fishes, amphibians and reptiles, and not in those of endothermic birds and mammals. Although NAH is known to be synthesized from l-His and acetyl-CoA by histidine N-acetyltransferase (HISAT; EC 2.3.1.33), the gene encoding HISAT has remained unknown for any organism.

Methods

HISAT was purified from the blue mackerel brain, and its partial amino acid sequences were analyzed using mass spectrometry and Edman degradation. Using the sequence information, the corresponding gene was cloned and sequenced. Recombinant proteins encoded by the fish gene and its human homologue were expressed in a cell-free translation system.

Results

HISAT was identified to be a protein encoded by a fish homologue of the human predicted gene NAT16 (N-acetyltransferase 16). HISAT is an unstable enzyme that is rapidly and irreversibly inactivated during preincubation at 37 °C in the absence of acetyl-CoA. In fish brain, the HISAT gene is expressed as two splice variants containing an identical ORF but differing lengths of 5′-UTR. Both variants are expressed exclusively in the fish brain and lens. Interestingly, the recombinant human NAT16 protein, unlike the recombinant fish HISAT, has only trace enzyme activity for NAH synthesis.

Conclusions

These results propose that the function of mammalian NAT16 has been altered from l-His acetylation (NAH synthesis) to another different biological role.

General significance

The molecular identification of HISAT will allow progress in the understanding of the physiological function of NAH in ectothermic vertebrates.     

Effects of N,N′-dicyclohexylcarbodiimide on isolated and reconstituted cytochrome b-c1 complex from bovine heart mitochondria

N,N′-Dicyclohexylcarbodiimide (DCCD) inhibits the activity of ubiquinol-cytochrome c reductase in the isolated and reconstitued mitochondrial cytochrome b-c₁ complex. DCCD inhibits equally electron flow and proton translocation (i.e., the $\text{H}{}^{\mathrm{+}}\text{e}{}^{\mathrm{?}}$ ratio is not affected) catalysed by the enzyme reconstituted into phospholipid vesicles. The inhibitory effects are accompanied by structural alterations in the polypeptide pattern of both isolated and reconstituted enzyme. Cross-linking was observed between subunits V (iron-sulfur protein) and VII, indicating that these polypeptides are in close proximity. A clear correlation was found between the kinetics of inhibition of enzymic activity and the cross-linking, suggesting that the two phenomena may be coupled. Binding of [¹⁴C]DCCD was also observed, to all subunits with the isolated enzyme and preferentially to cytochrome b with the reconstituted vesicles; in both cases, however, it was not correlated kinetically with the inhibition of the enzymic activity.     

N-2′-Acetoxybenzoyl derivatives of chitosan, N-desulphated heparin and 2-amino-2-deoxy-d-glucose

N-2′-Acetoxybenzoyl (aspirin) derivatives (degree of substitution 0·35–1·00) of chitosan, N-desulphated heparin and 2-amino-2-deoxy-d-glucose were prepared by methods that gave yields in the range 65–86%. The salicylate of chitosan was isolated with a 98% yeild. Aspirin or salicylic acid was released much more slowly from N-(2′-acetoxybenzoyl)-chitosan than from the salicylate of chitosan, and much faster at 37°C in 0·1 m NaOH solution than in 2% aqueous acetic acid solution. Salicylic acid was isolated from the dialysate (0·1 m NaOH solution) of N-(2′-acetoxybenzoyl)-chitosan.     

Induction of 6-thioguanine resistance in synchronized human fibroblast cells treated with methyl methanesulfonate, N-acetoxy-2-acetylaminofluorene and N-ethyl-N′-nitro-N-nitrosoguanidine

Chemical induction of 6-thioguanine resistance was studied in synchronized human fibroblast cells. Cells initially grown in a medium lacking arginine and glutamine for 24 h ceased DNA synthesis and failed to enter the S phase. After introduction of complete medium, the cells progressed to the S phase after 16 h. DNA synthesis peaked 20 h after removal of nutrient stress and declined.Mutations were induced in S-phase cells by methyl methanesulfonate (MMS), N-acetoxy-2-acetylaminofluorene (NA-AAF) and N-methyl-N′-nitro-N-nitrosoguanidine (MNNG). Chemical treatments resulted in an increase in the absolute number of mutant colonies and in a dose-dependent mutation frequency. In this report, we show that NA-AAF evokes a temporal pattern of mutation in synchronized cells, with such mutations being induced only during the S phase. Evidence indicates that presence of S-phase cells in the treated cultures is a prerequisite for the induction of mutations.     

Determination of nicotinamide N-oxide—a human excretory product

A method for the determination of nicotinamide N-oxide has been developed. It is based on the ability of the N-oxide to function as an electron acceptor in the xanthine oxidase catalyzed oxidation of xanthine. In simple mixtures the N-oxide can be converted quantitatively to nicotinamide and the latter determined by the cyanogen bromide method. The conversion is not always quantitative in complex mixtures, such as urine; an isotope dilution variation on the basic method permits the determination of the N-oxide in such situations. The basic method is applicable over the range 0.02–0.3 μmole of nicotinamide N-oxide.The new method has been used to verify the prominent excretory role of nicotinamide N-oxide in rodents. Application of the method to a study of human urines has permitted the detection of the N-oxide as an excretory metabolite in man. Only vanishingly small quantities of the N-oxide are excreted under normal conditions. However after the ingestion of 200 mg of nicotinamide, significant quantities of the N-oxide are detectable in human urine. Urine samples obtained from a number of other mammalian species contained little or no detectable nicotinamide N-oxide.     

Determination of asymmetric Nα-acetyldimethylarginine in humans: A phase II metabolite of asymmetric dimethylarginine

Asymmetric dimethylarginine (ADMA) is produced by protein methylation, a common mechanism of posttranslational protein modification. Elevated levels of ADMA lead to impaired endothelial nitric oxide production and subsequently to a range of cardiovascular and other diseases related to decreased nitric oxide production. Knowledge of the elimination pathways of ADMA and the possibility of influencing them is therefore of major clinical interest. One of these pathways is the N-acetylation and subsequent renal elimination of ADMA in the form of asymmetric N_α-acetyldimethylarginine (Ac-ADMA). In this work, we describe the first method to quantitatively determine Ac-ADMA in human plasma and urine. Ac-ADMA was separated by HPLC on a porous graphitic carbon column and selectively analyzed by tandem mass spectrometry. Ac-ADMA and the internal standard D₇-Ac-ADMA were synthesized in-house. Precision and accuracy of the method were better than 5% in plasma and urine quality control samples. First results obtained with this method in samples of healthy volunteers showed plasma levels of 0.643 ± 0.454 nmol/L and urine levels of 152.7 ± 76.7 nmol/L or 13.0 ± 8.9 nmol/mmol creatinine. The method is a suitable tool for investigating this currently mostly neglected ADMA elimination pathway.     

Comparison of mutagenicity and chemical properties of N-methyl-N′-alkyl-N-nitrosoureas

Thed mutagenic activities of 11 N-methyl-N′-alkyl-N-nitrosoureas were tested on Samonellatyphimurium TA1535 and compared with chemical properties (alkylating activity and decompostion rate). In their relative mutagenicities the N-nitrosoureas that had a cyclic N′-alkyl group showed far more mutagenic activity than those having a chain N′-alkyl group. M(1-A)NU and M(2-A)NU, which had the most bulky N′-alkyl group in this series, exhibited lethal effects at high concentrations. The mutagenicity showed a small positive correlation with decomposition rates but not with alkylating activities on 4-(p-nitrobenzyl_prridine. The highest mutagenicity in this series was observed in N-methyl-N′-cyclobutyl-N-nitrosourea.These results suggest that, in this series of N-methyl-M′-alkyl-N-nitrosoureas, structural differences in the N′-alkyl groups had great significance in mutagenicity.