Mutagenicities of 2,4- and 2,6-dinitrotoluenes and their reduced products in Salmonella typhimurium nitroreductase- and O-acetyltransferase-overproducing Ames test strains

Mutagenicities of 2,4- and 2,6-dinitrotoluene (2,4-and 2,6-DNT), and reduced metabolites formed by the incubation of 2,4- and 2,6-DNT with Salmonella typhimurium TA98, were tested using S. typhimurium YG strains possessing high level of nitroreductase (NR) and/or O-acetyltransferase (OAT) activities. All compounds tested showed greatest mutagenic activities toward strains YG1041 and YG1042, which possess high levels of NR and OAT activities. The relative mutagenic activities of 2,4-DNT and its related compounds toward YG1041 and YG1042 were aminonitrotoluenes (2A4NT, 4A2NT)<2,4-DNT<2,2′-dimethyl-5,5′-dinitroazoxybenzene (2,2′-DM-5,5′-DNAOB)4-hydroxylamino-2-nitrotoluene (4HA2NT)4,4′-dimethyl-3,3′-dinitroazoxybenzene (4,4′-DM-3,3′-DNAOB), and aminonitrotoluenes (2A4NT, 4A2NT)<2,4-DNT<4HA2NT4,4′-dimethyl-3,3′-dinitroazoxybenzene (4,4′-DM-3,3′-DNAOB)<2HA4NT, respectively. In addition, the relative mutagenic activities of 2,6-DNT and its related compounds toward YG1041 and YG1042 were 2,6-DNT<2-hydroxylamino-6-nitrotoluene (2HA6NT)<2,2′-dimethyl-3,3′-dinitroazoxybenzene (2,2′-DM-3,3′-DNAOB), and 2-amino-6-nitrotoluene (2A6NT)<2,6-DNT<2HA6NT, respectively. These results, together with previous findings, suggested that aminohydroxylamino dimethylazoxybenzenes or aminohydroxylamino dimethylazobenzenes produced either by the reduction of hydroxylaminonitrotoluenes or by the reduction of dimethyl dinitroazoxybenzenes are active metabolites responsible for the mutagenic activities of 2,4- and 2,6-DNT.     

Simultaneous determination of stable isotopically labelled l-histidine and urocanic acid in human plasma by stable isotope dilution mass spectrometry

A capillary gas chromatographic—mass spectrometric method for the simultaneous determination of stable isotopically labelled l-histidine (l-[3,3-²H₂,1′,3′-¹⁵N₂]histidine, l-His-[M + 4]) and urocanic acid ([3-²H,1′,3′-¹⁵N₂]urocanic acid, UA-[M + 3]) in human plasma was developed using dl-[2,3,3,5′-²H₄,2′-¹³C,1′,3′-¹⁵N₂]histidine (dl-His-[M + 7]) and [2,3,5′-²H₃,2′-¹³C,1′,3′-¹⁵N₂]urocanic acid (UA-[M + 6]) as internal standards. l-Histidine and urocanic acid were derivatized to ^αN-(trifluoroacetyl)-^imN-(ethoxycarbonyl)-l-histidine n-butyl ester and ^imN-(ethoxycarbonyl)urocanic acid n-butyl ester. Quantification was carried out by selected ion monitoring of the molecular ions of the respective derivatives of l-His-[M + 4], dl-His-[M + 7], UA-[M + 3] and UA-[M + 6]. The sensitivity, specificity, precision and accuracy of the method were demonstrated to be satisfactory for measuring plasma concentrations of l-His-[M + 4] and UA-[M + 3] following administration of trace amounts of l-His-[M + 4] to humans.     

Development,validation and characterization of an analytical method for the quantification of hydrolysable urinary metabolites and plasma protein adducts of 2,4- and 2,6-toluene diisocyanate, 1,5-naphthalene diisocyanate and 4,4'-methylenediphenyl diisocyanate

Occupational exposure to diisocyanates within the plastic industry causes irritation and disorders in the airway. The aim of this study was to develop, validate and characterize a method for the determination of 2,4-toluenediamine (2,4-TDA), 2,6-toluenediamine (2,6-TDA), 1,5-diaminonaphthalene (1,5-NDA) and 4,4′-methylenedianiline (4,4′-MDA) in hydrolysed urine and plasma, and to study the correlation between the plasma and urinary levels of these potential biomarkers of 2,4-toluene diisocyanate (2,4-TDI), 2,6-toluene diisocyanate (2,6-TDI), 1,5-naphthalene diisocyanate (1,5-NDI) and 4,4′-methylenediphenyl diisocyanate (4,4′-MDI), respectively. Samples were hydrolysed with 0.3 M NaOH at 100°C for 24 h. The diamines were extracted, derivatized with pentafluoropropionic acid anhydride, and quantified by selected ion monitoring on gas chromatography-mass spectrometry. The repeatability and reproducibility of the method were 7-18% and 7-19%, respectively. Dialysis experiments showed that the metabolites of 2,4-TDI, 2,6-TDI, 1,5-NDI and 4,4′-MDI in plasma were exclusively protein adducts. No free diamines were found in urine, indicating that all diisocyanate-related metabolites were in a conjugated form. For each diisocyanate-related biomarker, there were strongly significant correlations (p&lt;0.001) between individual levels of metabolites in plasma and urine, with Spearman's rank correlation coefficient (r_s) values of 0.74-0.90. The methods presented here will be valuable for the development of biological monitoring methods for diisocyanates.     

Solution structure investigations of olefin Pd(II) and Pt(II) complex ion pairs bearing α-diimine ligands by F, H-HOESY NMR

Complexes [M(η¹,η²-C₈H₁₂OMe)((2,6-(R)₂---C₆H₃)N=C(R′)---C(R′)=N((2,6-(R)₂---C₆H₃))]PF₆ (where M=Pd, R=H and R′₂=Me₂ (1), M=Pd, R=Me and R′₂=Me₂ (2), M=Pd, R=Et and R′₂=Me₂ (3), M=Pd, R=iPr and R′₂=Me₂ (4), M=Pd, R=iPr and R′₂=An (5), M=Pt, R=iPr and R′₂=An (6)) were synthesized by the reaction of [M(η¹,η²-C₈H₁₂OMe)Cl]₂ with the appropriate α-diimine ligand in the presence of NH₄PF₆. Their ion pair structure in solution was investigated by detecting dipolar interactions between protons belonging to the cation and fluorine nuclei of the anion (interionic contacts) in the ¹⁹F, ¹H-HOESY NMR spectra. In complexes 1–4, the anion in solution is located close to the peripheral protons of the α-diimine ligand and it interacts with the R′ protons and with the R protons that point toward the R′ groups. The steric protection of apical position exerted by the R substituents is clearly illustrated by the absence of interionic contacts between any protons of the cycloctenylmethoxy-moiety and the anion for R≥Me in 1–4. In complexes 5 and 6 the interactions between the anion and the peripheral N,N protons also predominate but other anion–cation orientations are significantly present and, consequently, the interionic structure is less specific.     

Half-sandwich Ru[9]aneS3 complexes structurally similar to antitumor-active organometallic piano-stool compounds: Preparation, structural characterization and in vitro cytotoxic activity

The preparation, structural characterization, and chemical behavior in aqueous solution of a series of new Ru[9]aneS₃ half-sandwich complexes of the type [Ru([9]aneS₃)Cl(NN)][CF₃SO₃] and [Ru([9]aneS₃)(dmso-S)(NN)][CF₃SO₃]₂ (5–15, NN = substituted bpy or 2 × 1-methylimidazole) are described. The X-ray structures of [Ru([9]aneS₃)Cl(3,3′-H₂dcbpy)][CF₃SO₃] (9) (3,3′-H₂dcbpy = 3,3′-dicarboxy-2,2′-bipyridine), [Ru([9]aneS₃)Cl(4,4′-dmobpy)][CF₃SO₃] (13) (4,4′-dmobpy = 4,4′-dimethoxy-2,2′-bipyridine), and [Ru([9]aneS₃)Cl(1-MeIm)₂][CF₃SO₃] (15) (1-MeIm = 1-methylimidazole) were also determined. The new compounds are structurally similar to anticancer-active organometallic half-sandwich complexes of formula [Ru(η⁶-arene)Cl(NN)][PF₆]. Three chloro compounds (5, 9, 15) were tested in vitro for cytotoxic activity against two human cancer cell lines in comparison with the previously described [Ru([9]aneS₃)Cl(en)][CF₃SO₃] (1, en = ethylenediamine), [Ru([9]aneS₃)Cl(bpy)][CF₃SO₃] (2), and with their common dmso precursor [Ru([9]aneS₃)Cl(dmso-S)₂][CF₃SO₃] (3). Only the ethylenediamine complex 1 showed some antiproliferative activity, ca. one order of magnitude lower than the reference organometallic half-sandwich compound RM175 that contains biphenyl instead of [9]aneS₃. This compound was further tested against a panel of human cancer cell lines (including one resistant to cisplatin).     

Microfluorometric analysis of Cl permeability and its relation to oscillatory Ca signalling in glucose-stimulated pancreatic β-cells

The cytoplasmic concentrations of Cl⁻([Cl⁻]_i) and Ca²⁺ ([Ca²⁺]_i) were measured with the fluorescent indicators N-(ethoxycarbonylmethyl)-6-methoxyquinilinum bromide (MQAE) and fura-2 in pancreatic β-cells isolated from ob/ob mice. Steady-state [Cl⁻]_i in unstimulated β-cells was 34 mM, which is higher than expected from a passive distribution. Increase of the glucose concentration from 3 to 20 mM resulted in an accelerated entry of Cl⁻ into β-cells depleted of this ion. The exposure to 20 mM glucose did not affect steady-state [Cl⁻]_i either in the absence or presence of furosemide inhibition of Na⁺, K⁺, 2 Cl⁻ co-transport. Glucose-induced oscillations of [Ca²⁺]_i were transformed into sustained elevation in the presence of 4,4′ diisothiocyanato-dihydrostilbene-2,2′-disulfonic acid (H₂DIDS). A similar effect was noted when replacing 25% of extracellular Cl⁻ with the more easily permeating anions SCN⁻, I⁻, NO₃⁻ or Br⁻. It is concluded that glucose stimulation of the β-cells is coupled to an increase in their Cl⁻ permeability and that the oscillatory Ca²⁺ signalling is critically dependent on transmembrane Cl⁻ fluxes.     

Methacholine-induced cGMP production is regulated by nitric oxide generation in rabbit submandibular gland cells

Guanosine 3′,5′-monophosphate (cGMP) is an intracellular messenger in various kinds of cell. We investigated the regulation of cGMP production by nitric oxide (NO) in rabbit submandibular gland cells. Methacholine, a muscarinic cholinergic agonist, stimulated cGMP production in a dose- and time-dependent manner, but the α-agonist phenylephrine, substance P and the β-agonist isoproterenol failed to evoke cGMP production. In fura-2-loaded cells, methacholine induced an increase in intracellular Ca²⁺ ([Ca²⁺]_i) in a concentration-dependent manner, which was similar to that for cGMP production. When the external Ca²⁺ was chelated with EGTA, methacholine failed to induce cGMP production. Ca²⁺ ionophore A23187 and thapsigargin, which induce the increase in [Ca²⁺]_i without activation of Ca²⁺-mobilizing receptors, mimicked the effect of methacholine. cGMP production induced by methacholine, A23187 and thapsigargin was clearly inhibited by N^G-nitro- -arginine methylester (L-NAME), a specific inhibitor of nitric oxide synthase (NOS). S-Nitroso-N-acetyl- -penicillamine (SNAP), a NO donor, induced cGMP formation. In the lysate of rabbit submandibular gland cells, Ca²⁺-regulated nitric oxide synthase activity was detected. These findings suggest that cGMP production induced by the activation of muscarinic cholinergic receptors is regulated by NO generation via the increase in [Ca²⁺]_i.     

Gas chromatographic–mass spectrometric determination of α-ketoisocaproic acid and [H7]α-ketoisocaproic acid in plasma after derivatization with N-phenyl-1,2-phenylenediamine

A method for determination of α-ketoisocaproic acid (KIC) and [4,5,5,5,6,6,6-²H₇]α-ketoisocaproic acid ([²H₇]KIC) in rat plasma was developed using gas chromatography–mass spectrometry-selected ion monitoring (GC–MS-SIM). [5,5,5-²H₃]α-Ketoisocaproic acid ([²H₃]KIC) was used as an analytical internal standard to account for losses associated with the extraction, derivatization and chromatography. The keto acids were extracted by cation-exchange chromatography using BondElut SCX cartridge and derivatized with N-phenyl-1,2-phenylenediamine to form N-phenylquinoxalinone derivatives. Quantitation was performed by SIM of the respective molecular ions at m/z 278, 281 and 285 for the derivatives of KIC, [²H₃]KIC and [²H₇]KIC on the electron impact method. The limit of detection was found to be 70 fmol per injection (S/N=3) and the limit of quantitation for [²H₇]KIC was around 50 nM in rat plasma. Endogenous KIC concentrations in 50 μl of rat plasma were measured with relative intra- and inter-day precision of 4.0% and 3.3%, respectively. The intra- and inter-day precision for [²H₇]KIC spiked to rat plasma in the range of 0.1 to 10 μM gave good reproducibility with relative standard deviation (RSD) of 6.5% and 5.4%, respectively. The intra- and inter-day relative errors (RE) for [²H₇]KIC were less than 6.4% and 3.8%, respectively. The method was applied to determine the plasma concentration of [²H₇]KIC after an intravenous administration of [²H₇]KIC in rat.     

DNA adduct formation in human hepatoma cells treated with 3-nitrobenzanthrone: analysis by the P-postlabeling method

3-Nitrobenzanthrone (3-nitro-7H-benz[d,e]anthracen-7-one, 3-NBA) is a powerful mutagen and a suspected human carcinogen existing in diesel exhaust and airborne particulates. Recently, one of the major presumed metabolites of 3-NBA, 3-aminobenzanthrone (3-ABA), was detected in human urine samples. Here we analyzed DNA adducts formed in 3-NBA-exposed human hepatoma HepG2 cells by a ³²P-postlabeling/thin layer chromatography (TLC) method and a ³²P-postlabeling/polyacrylamide gel electrophoresis (PAGE) method. With HepG2 cells exposed to 3-NBA (0.36–36.4 μM) for 3 h, we obtained three spots or bands corresponding to adducted nucleotides. Two were assigned as 2-(2′-deoxyadenosin-N⁶-yl)-3-aminobenzanthrone-3′-phosphate (dA3′p-N⁶-C2-ABA) and 2-(2′-deoxyguanosin-N²-yl)-3-aminobenzanthrone-3′-phosphate (dG3′p-N²-C2-ABA), with identical mobilities to those of synthetic standards on PAGE analysis. The chemical structure of the substance corresponding to the other spot or band could not be identified. Quantitative analyses revealed that the major adduct was dA3′p-N⁶-C2-ABA and its relative adduct labeling (RAL) value at 36.4 μM of 3-NBA was 200.8 ± 86.1/10⁸ nucleotide.     

P nuclear magnetic resonance study of the interaction of multidentate amines with zinc(II) bis(O,O′-di-iso-butyldithiophosphate)

³¹P NMR has been employed to study the interaction between zinc(II) bis(O,O′-di-iso-butyldithiophosphate), Zn[S₂P(OⁱBu)₂]₂, and four multidentate amines (diethylenetriamine, triethylenetetramine, tetraethylenepentamine and pentaethylenehexamine) in chloroform at 294 K. The major interaction of Zn[S₂P(OⁱBu)₂]₂ and these polyamines involves displacement of the {S₂P(OⁱBu)₂} ligands from the zinc giving [Zn(amine)]²⁺ and [S₂P(OⁱBu)₂]⁻ ions in solution. The magnitudes of the equilibrium constants, K₁ (=[{Zn(amine)}²⁺][{DDP}⁻]₂/[Zn(DDP)₂][amine]), have been evaluated in the cases of triethylenetetramine (20.0 l mol⁻¹), tetraethylenepentamine (19.1 l mol⁻¹) and pentaethylenehexamine (1.58 l mol⁻¹). Crystalline 1:1 ionic complexes have also been isolated from these systems and characterised.     

Body nitrosation potential measured by a novel N breath test

Oxygenated nitrogen species, for example, the protonated form of nitrous acid (H₂ONO⁺), dinitrogentrioxide (N₂O₃), dinitrogentetroxide (N_2O4), or peroxynitrite (ONOO⁻), can react with amines to form molecular nitrogen. These reactions can occur spontaneously with primary aliphatic amines or via cytochrome P450 catalysed reactions with secondary amines. In principle measurements of the excretion of the molecular nitrogen generated by these reactions could be used as an index of the levels of oxygenated nitrogen compounds acting as nitrosating agents. To test this idea, [¹⁵N₂]urea (3 mmol) was administered orally to five patients infected with Helicobacter pylori (as diagnosed by the [¹³C]urea breath test) and to four healthy volunteers. All participants ingested 3-mmol sodium nitrate as a precursor for NA 5 min before the ingestion of the nitrogen tracer. During the test the participants breathed 100% oxygen to increase the sensitivity of detection of endogenous molecular nitrogen. After the administration of [¹⁵N₂]urea, the patients with H. pylori showed significantly increased ¹⁵N enrichments of exhaled N₂, expressed as δ value (‰), compared with healthy volunteers (patients: 3.5 ± 0.9 vs. volunteers: 1.3 ± 0.4; p < .05). We speculate that the endogenous production of molecular nitrogen is a protective process controlling the body NO and nitrite levels. The ¹⁵N breath technique allows the noninvasive estimation of the body nitrosation and could indicate the health risk, possibly the oxidative stress status, caused by highly reactive oxygenated nitrogen species and carbenium ion intermediates.     

Induction of SCEs in CHL cells by dichlorobiphenyl derivative water pollutants, 2-phenylbenzotriazole (PBTA) congeners and river water concentrates

We recently identified dichlorobiphenyl (DCB) derivatives and 2-phenylbenzotriazole (PBTA) congeners as major mutagenic constituents of the waters of the Waka River and the Yodo River system in Japan, respectively. In this study we examined sister chromatid exchange (SCE) induction by two dichlorobiphenyl derivatives, 3,3′-dichlorobenzidine (DCB, 4,4′-diamino-3,3′-dichlorobiphenyl) and 4,4′-diamino-3,3′-dichloro-5-nitrobiphenyl (5-nitro-DCB); three PBTA congeners, 2-[2-(acetylamino)-4-[bis(2-methoxyethyl)amino]-5-methoxyphenyl]-5-amino-7-bromo-4-chloro-2H-benzotriazole (PBTA-1), 2-[2-(acetylamino)-4-[N-(2-cyanoethyl)ethylamino]-5-methoxyphenyl]-5-amino-7-bromo-4-chloro-2H-benzotriazole (PBTA-2), and 2-[2-(acetylamino)amino]-4-[bis(2-hydroxyethyl)amino]-5-methoxyphenyl]-5-amino-7-bromo-4-chloro-2H-benzotriazole (PBTA-6); and water concentrates from the Waka River in Chinese hamster lung (CHL) cells. Concentration-dependent induction of SCE was found for all DCBs and PBTAs examined in the presence of S9 mix, and statistically significant increases of SCEs were detected at 2 μg per ml of medium or higher concentrations. SCE induction of MeIQx was examined to compare genotoxic activities of these water pollutants. According to the results, a ranking of the SCE-inducing potency of these compounds is the following: 5-nitro-DCB ≈ MeIQx > PBTA6 > PBTA-1 ≈ PBTA-2 > DCB.Water samples collected at a site at the Waka River showed concentration-related increases in SCEs at 6.25–18.75 ml-equivalent of river water per ml of medium with S9 mix. The concentrations of 5-nitro-DCB and DCB in the river water samples were from 2.5 to 19.4 ng/l and from 4100 to 18,900 ng/l, respectively. However, these chemicals showed only small contribution to SCE induction by the Waka River water.     

Kinetics and mechanism of CO substitution of [η-CpFe(CO)3]PF6 with PPh3 in the presence of substituted pyridine N-oxide

The kinetics of substitution reactions of [η-CpFe(CO)₃]PF₆ with PPh₃ in the presence of R-PyOs have been studied. For all the R-PyOs (R = 4-OMe, 4-Me, 3,4-(CH)₄, 4-Ph, 3-Me, 2,3-(CH)₄, 2,6-Me₂, 2-Me), the reactions yeild the same product [η⁵-CpFe(CO)₂PPh₃]PF₆, according to a second-order rate law that is first order in concentrations of [η⁵-CpFe(CO)₃]PF₆ and of R-PyO but zero order in PPh₃ concentration. These results, along with the dependence of the reaction rate on the nature of R-PyO, are consistent with an associative mechanism. Activation parameters further support the bimmolecular nature of the reactions: ΔH^≠ = 13.4 ± 0.4 kcal mol⁻¹, ΔS^≠ = −19.1 ± 1.3 cal k⁻¹ mol⁻¹ for 4-PhPyO; ΔH^≠ = 12.3 ± 0.3 kcal mol⁻¹, ΔS^≠ = 24.7 ±1.0 cal K⁻¹ mol⁻¹ for 2-MePyO. For the various substituted pyridine N-oxides studied in this paper, the rates of reaction increase with the increasing electron-donating abilities of the substituents on the pyridine ring or N-oxide basicities, but decrease with increasing ¹⁷O chemical shifts of the N-oxides. Electronic and steric factors contributing to the reactivity of pyridine N-oxides have been quantitatively assessed.     

Postlabelling analysis of DNA adducts formed in human hepatoma cells treated with 3-nitrobenzanthrone

3-Nitrobenzanthrone (NBA) is one of the most mutagenic nitroaromatic compounds that has been found recently in diesel exhaust and airborne particles. A [³²P]-postlabelling analysis was carried out to examine the adducts in DNA from human hepatoma HepG2 cells treated with NBA. Two major and two minor adduct spots were obtained in the analysis. The structure of the compound obtained from one of the minor adduct spots was identified to be N-acetyl-3-amino-2-(2′-deoxyguanosin-3′,5′-bisphosphate-8-yl)-benzanthrone, based on identical mobility of the compound with that of synthetic standards in thin-layer chromatography and high performance liquid chromatography. This substance is the identical adduct found in our previous in vitro study. The yet-unidentified major adduct spots may be guanosin- and adenosin-benzanthrone adducts without the N-acetyl group.     

Gramicidin S analogs with a D-Ala, Gly, or L-Ala residue in place of the D-Phe residue: molecular conformations and interactions with phospholipid membrane

The proton nmr and CD spectra of gramicidin S (GS) cyclic-(Val^1,1′-Orn^2,2′-Leu^3,3′-D-Phe^4,4′-Pro^5,5′)₂ and of GS analogs—namely, [D-Ala^4,4′]-GS, [Gly^4,4′]-GS, and [L-Ala^4,4′]-GS—were analyzed. The molecular conformation of [D-Ala^4,4′]-GS is similar to that of GS, with the trans form about the D-Ala-Pro peptide bond. The molecular conformation of [Gly^4,4′]-GS depends on the solvent composition of dimethylsulfoxide-d₆/trifluoroethanol (DMSO)-d₆/TFE and DMSO-d₆/H₂O as well as the solute concentration. In DMSO-d₆ solution, [Gly^4,4′]-GS forms the GS-type conformation of the monomer at lower concentration. At higher concentration, the GS-type conformer is converted to the other one that forms molecular aggregates. The cis form about the X-Pro peptide bonds is found for [Gly^4,4′]-GS and [L-Ala^4,4′]-GS in DMSO-d₆ and for [L-Ala^4,4′]-GS in TFE solution. The large temperature dependences of α-proton chemical shifts of [L-Ala^4,4′]-GS in DMSO-d₆ solution indicate that the conformer equilibrium changes with temperature. The GS-type conformation is not formed in [L-Ala^4,4′]-GS. The two active peptide analogs, [D-Ala^4,4′]-GS and [Gly^4,4′]-GS, interact with the phospholipid membrane, taking the GS-type conformation. By contrast, an inactive analog, [L-Ala^4,4′]-GS, does not interact with phospholipid membrane. The activities of GS analogs are found to correlate to the formation of the GS-type conformation upon binding with phospholipid membrane.     

Biosynthesis of methyl chloride in the fungusPhellinus pomaceus

The biosynthetic origin of themethyl group in the methyl chloride produced by cultures ofPhellinus pomaceus (Pers.) Maire has been investigated using stable isotope labeled substrates. Feeding ofd-[6,6-²H₂] glucose,Dl-[3,3-²H₂] serine andl-[methyl-²H₃] methionine led to the production of deuterated methyl chloride in which the major labeled species contained 2, 2, and 3 deuterium atoms, respectively. The data are consistent with the methyl chloride produced by this organism being derived solely from methionine with retention of all of the methyl protons.Abbreviation SAM S-adenosylmethionine - FH₄ tetrahydrofolate - N⁵-CH₃FH₄ N⁵-methyltetrahydrofolate - B₁₂ cobalamin     

Synthesis and cytotoxic activity of some novel polycyclic gamma-butyrolactones

Baeyer–Villiger oxidation of 5-aryl-7,11,11-trimethyltricyclo[5.4.0.0^3,6]-undec-1-en-4-ones 4a–h by H₂O₂ and formic acid in methanol yields mixtures of 3b,7,7-trimethyl-3-phenyl-3,3a,3b,4,5,6,7,8a-octahydro-1H-indeno-[1,2-c]furan-1-ones 8a–h and 3b,7,7-trimethyl-3-phenyl-3,3a,3b,4,5,6,7,8a-octahydro-1H-indeno-[1,2-c]furan-2-ones 9a–h in high yields. The obtained butyrolactones 8a–h display cytotoxic activity against a number of human cancer cells.     

Synthesis of Neu5Ac- and Neu5Gc-α-(2→6′)-lactosamine 3-aminopropyl glycosides

In order to prepare 3-aminopropyl glycosides of Neu5Ac-α-(2→6′)-lactosamine trisaccharide 1, and its N-glycolyl containing analogue Neu5Gc-α-(2→6′)-lactosamine 2, a series of lactosamine acceptors with two, three, and four free OH groups in the galactose residue was studied in glycosylations with a conventional sialyl donor phenyl [methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-2-thio- -glycero-α- and β- -galacto-2-nonulopyranosid]onates (3) and a new donor phenyl [methyl 4,7,8,9-tetra-O-acetyl-5-(N-tert-butoxycarbonylacetamido)-3,5-dideoxy-2-thio- -glycero-α- and β- -galacto-2-nonulopyranosid]onates (4), respectively. The lactosamine 4′,6′-diol acceptor was found to be the most efficient in glycosylation with both 3 and 4, while imide-type donor 4 gave slightly higher yields with all acceptors, and isolation of the reaction products was more convenient. In the trisaccharides, obtained by glycosylation with donor 4, the 5-(N-tert-butoxycarbonylacetamido) moiety in the neuraminic acid could be efficiently transformed into the desired N-glycolyl fragment, indicating that such protected oligosaccharide derivatives are valuable precursors of sialo-oligosaccharides containing N-modified analogues of Neu5Ac.     

Determination of serum unconjugated estrone, estradiol-17β and estriol during pregnancy by selected ion monitoring

A simple, rapid and highly specific method by selected ion monitoring (SIM), using 9α,11α-[²H₂]estrone, [2,4-²H₂]estradiol-17β and 2,4-[²H₂]estriol as internal standards, was developed for the determination of serum estrogens during pregnancy. Serum samples were submitted to a simple extraction procedure and were analysed after formation of the trifluoroacetic anhydride derivative. The inter-assay coefficients of variation for estrone, estradiol-17β and estriol were 3.73%, 3.42% and 3.49%, respectively. The results obtained by SIM were compared with analysis performed using radioimmunoassay.     

Reversible reaction via a carbanion intermediate in the elimination of ammonia from l-histidine catalysed by histidine ammonia-lyase

l-[5′-²H₂]Histidine was used as a substrate to investigate the enzymatic reaction mechanism with histidine ammonia-lyase from Pseudomonas fluorescens. The study was performed to determine the exchange rate of deuterium at C-5′ of the imidazole ring with solvent hydrogen relative to the net urocanic acid production. The extent of hydrogen exchange at C-5′ of histidine or urocanic acid was measured by gas chromatography—mass spectrometry—selected ion monitoring, monitoring the molecular ion intensities of the respective gas chromatographic derivatives, at m/z 380 and 379 for histidine and at m/z 267 and 266 for urocanic acid. The observed hydrogen exchange at C-5′ suggested a reversible mechanism via a carbanion intermediate in the reaction with histidine ammonia-lyase.