Biological oxidation of nitrogen in organic compounds and disposition of N-oxidized products

Gut microbiota in reductive drug metabolism

Gut bacteria are predominant microorganisms in the gut microbiota and have been recognized to mediate a variety of biotransformations of xenobiotic compounds in the gut. This review is focused on one of the gut bacterial xenobiotic metabolisms, reduction. Xenobiotics undergo different types of reductive metabolisms depending on chemically distinct groups: azo (-NN-), nitro (-NO₂), alkene (-CC-), ketone (-CO), N-oxide (-NO), and sulfoxide (-SO). In this review, we have provided select examples of drugs in six chemically distinct groups that are known or suspected to be subjected to the reduction by gut bacteria. For some drugs, responsible enzymes in specific gut bacteria have been identified and characterized, but for many drugs, only circumstantial evidence is available that indicates gut bacteria-mediated reductive metabolism. The physiological roles of even known gut bacterial enzymes have not been well defined.

Efficient Synthesis of Trifluoromethyl Amines through a Formal Umpolung Strategy from the Bench-Stable Precursor (Me4 N)SCF3

Reported herein is the one-pot synthesis of trifluoromethylated amines at room temperature using the bench-stable (Me4 N)SCF3 reagent and AgF. The method is rapid, operationally simple and highly selective. It proceeds via a formal umpolung reaction of the SCF3 with the amine, giving quantitative formation of thiocarbamoyl fluoride intermediates within minutes that can readily be transformed to N-CF3 . The mildness and high functional group tolerance render the method highly attractive for the late-stage introduction of trifluoromethyl groups on amines, as demonstrated herein for a range of pharmaceutically relevant drug molecules.

Oxidation of quinolones with peracids (an in situ EPR study)

4-Oxoquinoline derivatives (quinolones) represent heterocyclic compounds with a variety of biological activities, along with interesting chemical reactivity. The quinolone derivatives possessing secondary amino hydrogen at the nitrogen of the enaminone system are oxidized with 3-chloroperbenzoic acid to nitroxide radicals in the primary step while maintaining their 4-pyridone ring. Otherwise, N-methyl substituted quinolones also form nitroxide radicals coupled with the opening of the 4-pyridone ring in a gradual oxidation of the methyl group via the nitrone-nitroxide spin-adduct cycle. This was confirmed in an analogous oxidation using N,N-dimethylaniline as a model compound. N-Ethyl quinolones in contrast to its N-methyl analog form only one nitroxide radical without a further degradation.

An experimental and computational study on the dissociation behavior of hydroxypyridine N-oxides in atmospheric pressure ionization mass spectrometry

A tandem mass spectrometric study of protonated isomeric hydroxypyridine N-oxides was carried out with a hybrid quadrupole/time-of-flight mass spectrometer coupled with different atmospheric pressure ionization sources. The behavior observed in the collision-induced dissociation (CID) mass spectra of the parent cations, was similar irrespective of the source employed. However, there were intrinsic differences in the intensities of the two fragments observed for each isomer. The major fragment because of elimination of a hydroxyl radical, dominated the CID spectra (in contrast with weaker water loss) at different energy thresholds. Therefore, it was possible to differentiate both isomers at collision energies above 13 eV by comparing the ratio of intensities of the major fragment relative to the precursor cation. In addition, quantum chemical calculations at the B3LYP/6-31 + + G(d,p) level of theory were performed for the protonated isomers of hydroxypyridine N-oxide and their radical cation products in order to gain insight into the major routes of dissociation. The results suggest that dissociation from the lowest triplet excited state of the protonated species would provide a reasonable rationalization for the difference in behavior of both isomers.

Functional interaction of nitrogenous organic bases with cytochrome P450: A critical assessment and update of substrate features and predicted key active-site elements steering the access, binding, and orientation of amines

The widespread use of nitrogenous organic bases as environmental chemicals, food additives, and clinically important drugs necessitates precise knowledge about the molecular principles governing biotransformation of this category of substrates. In this regard, analysis of the topological background of complex formation between amines and P450s, acting as major catalysts in C- and N-oxidative attack, is of paramount importance. Thus, progress in collaborative investigations, combining physico-chemical techniques with chemical-modification as well as genetic engineering experiments, enables substantiation of hypothetical work resulting from the design of pharmacophores or homology modelling of P450s. Based on a general, CYP2D6-related construct, the majority of prospective amine-docking residues was found to cluster near the distal heme face in the six known SRSs, made up by the highly variant helices B', F and G as well as the N-terminal portion of helix C and certain beta-structures. Most of the contact sites examined show a frequency of conservation < 20%, hinting at the requirement of some degree of conformational versatility, while a limited number of amino acids exhibiting a higher level of conservation reside close to the heme core. Some key determinants may have a dual role in amine binding and/or maintenance of protein integrity. Importantly, a series of non-SRS elements are likely to be operative via long-range effects. While hydrophobic mechanisms appear to dominate orientation of the nitrogenous compounds toward the iron-oxene species, polar residues seem to foster binding events through H-bonding or salt-bridge formation. Careful uncovering of structure-function relationships in amine-enzyme association together with recently developed unsupervised machine learning approaches will be helpful in both tailoring of novel amine-type drugs and early elimination of potentially toxic or mutagenic candidates. Also, chimeragenesis might serve in the construction of more efficient P450s for activation of amine drugs and/or bioremediation.

Models and mechanisms of O-O bond activation by cytochrome P450. A critical assessment of the potential role of multiple active intermediates in oxidative catalysis

Cytochrome P450 enzymes promote a number of oxidative biotransformations including the hydroxylation of unactivated hydrocarbons. Whereas the long-standing consensus view of the P450 mechanism implicates a high-valent iron-oxene species as the predominant oxidant in the radicalar hydrogen abstraction/oxygen rebound pathway, more recent studies on isotope partitioning, product rearrangements with 'radical clocks', and the impact of threonine mutagenesis in P450s on hydroxylation rates support the notion of the nucleophilic and/or electrophilic (hydro)peroxo-iron intermediate(s) to be operative in P450 catalysis in addition to the electrophilic oxenoid-iron entity; this may contribute to the remarkable versatility of P450s in substrate modification. Precedent to this mechanistic concept is given by studies with natural and synthetic P450 biomimics. While the concept of an alternative electrophilic oxidant necessitates C-H hydroxylation to be brought about by a cationic insertion process, recent calculations employing density functional theory favour a 'two-state reactivity' scenario, implicating the usual ferryl-dependent oxygen rebound pathway to proceed via two spin states (doublet and quartet); state crossing is thought to be associated with either an insertion or a radicalar mechanism. Hence, challenge to future strategies should be to fold the disparate and sometimes contradictory data into a harmonized overall picture.

Effects of 4-alkylmorpholine N-oxides on ATP-producing processes in Ehrlich ascites and L1210 leukaemia cells

The main purpose of the present investigation was to study the effect of the homologous series of 4-alkylmorpholine N-oxides on ATP-producing processes in Ehrlich ascites and L1210 murine leukaemia cells. The effects on aerobic glucose consumption, lactic acid formation, content of total (T-SH) and non-protein thiol groups (NP-SH), endogenous and exogenous respiration and the level of ATP in tumour cells incubated in vitro were investigated. 4-Dodecylmorpholine N-oxide (DMNO), one of the most active compounds, decreased the level of ATP immediately after addition to the suspension of Ehrlich cells in an ice bath. After 2 h incubation at 37 degrees C the drop in the ATP level was much lower. A possible explanation for the decrease in the ATP level might be interaction of the amine oxide with the cell membrane.

N-oxidative transformation of free and N-substituted amine functions by cytochrome P450 as means of bioactivation and detoxication

Indirect evidence for the participation of cytochrome P450 (P450) in the microsomal N-oxygenation of primary and N-substituted amine functions is presented by studies employing diagnostic modifiers of the hemoprotein system as well as immunochemical approaches. Experiments with recombinant hemoproteins or isozymes purified from the tissues of various animal species support the results obtained by the inhibitor assays. Amine substrates and the redox proteins of the microsomal electron transfer chain reveal to be mutually beneficial in interactions with P450s. Numerous N-substituted amines undergo P450-catalyzed N-oxidative transformation despite the presence of accessible alpha-C hydrogens in these structures rather thought to favor N-dealkylation. In these instances, stabilization of the initially formed aminium radicals by the specific active site orientation of the particular P450s obviously permits oxygen rebound. Apart from common iron-oxenoid chemistry involving a (FeO)3+ species, iron-bound hydroperoxide, (FeO2H)3+, appears to act as an electrophilic oxidant with certain N-substituted amines and P450 subforms. Generally, P450-mediated N-oxygenation of amines can produce cytotoxic and mutagenic metabolites, but equally can well yield hydrophilic products, that are readily excreted and thus promote detoxication.

In vitro metabolism of the analgesic agent, tramadol-N-oxide, in mouse, rat, and human

Tramadol-N-oxide (TNO, RWJ-38705) is a new analgesic agent, which is believed to produce its analgesic effect following metabolic conversion to tramadol. In the present study, API ionspray-MS and MS/MS techniques were used to profile the in vitro metabolism of TNO in mouse, rat, and human hepatic S9 fractions in the presence of an NADPH generating system. Unchanged TNO represented 60, 24, and 26% of the sample in mouse, rat, and human, respectively. Tramadol, and seven other metabolites were profiled and tentatively identified on the basis of MS analysis and by comparison to synthetic reference samples. TNO metabolites were formed via four Phase I reactions: (1) N-oxide reduction, (2) O-demethylation, (3) N-demethylation, and (4) cyclohexylhydroxylation. TNO was found to be substantially metabolized in hepatic S9 from all three species. The metabolism of TNO to tramadol via N-oxide reduction was greater in rat and human than in mouse.

Cytoxicity of 1-alkylperhydroazepine N-oxides and quantitative structure-activity relationships

A new class of nonaromatic amine oxides was tested for cytotoxic activity. The main aim of the present investigation was to screen a series of 1-alkylperhydroazepine N-oxides for in vitro cytotoxicity and to find out whether there is a quantitative structure-activity correlation (QSAR) between cytotoxic effect and structure (as a structural parameter the number of carbon atoms m in the alkyl chain was used). Cytotoxicity was determined here by inhibition of incorporation of [14C]adenine into nucleic acid or [14C]valine into proteins in Ehrlich ascites carcinoma (EAC) cells. On the basis of primary screening, one of the most active compounds, namely 1-tetradecylperhydroazepine N-oxide (TPNO), was chosen for further biochemical study. The drug inhibited the incorporation rate of [14C] labeled precursors (adenine, thymidine, uridine, valine) into appropriate macromolecules of Ehrlich cells. The extent of inhibition was dependent on both time and drug concentration. The lengthening of the alkyl chain in 1-alkylperhydroazepine N-oxides positively affected their cytotoxic activity in EAC cells. For these compounds the optimal m value is 12-14.

Effects of 1-tetradecylperhydroazepine and 1-pentadecylpiperidine N-oxides on Ehrlich ascites mitochondria

Non-aromatic amine oxides are widely known and used compounds. A great number of amine oxides occurring in nature, or prepared synthetically, are biologically active compounds (antimetabolites and chemotherapics, cancerostatic compounds, etc.). From seven series of newly synthesized amine oxides (63 compounds), 1-alkylperhydroazepine N-oxides (PHNO) and 1-alkylpiperadine N-oxides (PINO) have been chosen for further investigation. The effects of 8 derivatives of PHNO and 8 derivatives of PINO on state 3 and 4 respiration of Ehrlich ascites mitochondria (EAM) have been studied. Derivatives with longer side-chain significantly affected respiration of EAM according to the substrates used. To elucidate the mode of action, the most potent amine oxides from each series, 1-tetradecylperhydroazepine N-oxide (tPHNO) and 1-pentadecylpiperidine N-oxide (pPINO) have been chosen for further study. Both amine oxides stimulated state 4 respiration with glutamate-malate and succinate as substrates. The effect on state 3 respiration depended on the substrates used. Both tPHNO and pPINO were able to release respiration of EAM previously inhibited by oligomycin, both decreased the level of ATP in EAM. ATPase activity was significantly stimulated by both drugs only in higher concentrations. A possible mode of action of amine oxides on oxidative phosphorylation and the relationship between chemical structure are discussed.

Expression of a bacterial gene in transgenic plants confers resistance to the herbicide phenmedipham

Tobacco plants were genetically engineered to express a detoxifying pathway for the herbicide phenmedipham. A gene from Arthrobacter oxidans strain P52 that encodes an enzyme catalysing the hydrolytic cleavage of the carbamate compound phenmedipham has recently been cloned and sequenced. The coding sequence was fused with a cauliflower mosaic virus 35S promoter and introduced into tobacco plants by Agrobacterium-mediated gene transfer. Transgenic plants expressing high levels of phenmedipham hydrolase exhibited resistance when sprayed with the herbicide at up to ten times the usual field application rate.

Regulatory mechanisms in the activation of nitrogenous compounds by mammalian cytochrome P-450 isozymes

Metabolic activation of nitrogenous compounds by the cytochrome P-450 system is a highly complex process. Inherent substrate factors, such as basicity, electronic state, lipophilicity, and conformation control binding of the diverse classes of amines to cytochrome P-450. Accommodation of these compounds in the enzyme cavity and proper orientation of the molecules are governed by intrinsic properties of the peptide structure of cytochrome P-450, which may be subject to modification by the action of effectors. On the membrane level, phospholipid might have some impact on substrate binding. On the other hand, bound amine substrate is beneficial to the productive interaction of the electron transport chains with the terminal acceptor, improving economy of the system. Certain amines appear to regulate O2 association with cytochrome P-450 and stabilize the various oxy species formed. Considering the selective prerequisites for oxidative attack by cytochrome P-450 at vulnerable nitrogen centers, many cytotoxic amines belonging to the category of relatively rigid, planar molecules undergo N-oxidative activation by the cytochrome P-450IA subfamily, while more bulky amines with flexible conformation are N-oxygenated preferentially by phenobarbital-inducible cytochromes P-450. Small differences in protein structure between the various cytochrome P-450 subforms might serve to stabilize aminium radicals to permit oxygen rebound. Collectively, the selective regulatory mechanisms operative in the bioactivation of nitrogen-containing compounds appear to be determined largely by the type of substrate used and the isozyme involved in catalysis. With respect to the latter, the interplay of the multiple cytochromes P-450 in the various organs of animal species thus serves to rationalize the differences in the particular selectivities for amine substrates. These are responsible for the mode and/or extent to which activation of nitrogenous compounds, including promutagens and procarcinogens, occurs, and this may explain the tissue-specific response to the tumorigenic action of these agents.

Biochemical basis of cytotoxic activity of some new N'-oxides of N',N'-dimethylaminoalkylamides of dodecanoic acid

The objective of the present investigation was to screen a series of new N'-oxides of N',N'-dimethylaminoalkylamides of dodecanoic acid for activity in vitro and to investigate the biochemical mode of action. On the basis of primary screening, one of the most active compounds, namely the N'-oxide of 10-(N',N'-dimethylaminodecyl)amide of dodecanoic acid (n = 10) was chosen for detailed biochemical study. This compound inhibited the incorporation of 14C-precursors (adenine, valine, thymidine, uridine) into appropriate macromolecules of P388 murine leukemia and Ehrlich ascites carcinoma cells. The amine oxide also interfered with energy-yielding processes (aerobic glycolysis, endogenous respiration). Cytotoxicity is a consequence of the cytolytic activity of the compounds mentioned above. Membranous effects were demonstrated by the measuring of the release of cytoplasmic materials absorbing at 260 and 280 nm, marker enzyme activities (LDH, MDH), release of protein from the cells into the culture medium, as well as by morphological examination. It is evident that the site of action of the amine oxides investigated was the biological membrane which, after interaction with the amine oxides, showed changes in molecular organization and osmotic and permeability characteristics.

Chemical modification of lysine residues in cytochrome P450LM2 (P450IIB4): influence on heme liganding of arylamines

Treatment of cytochrome P450LM2 with fluorescein isothiocyanate to introduce up to two equivalents of fluorophore per polypeptide chain resulted in the selective derivatization of lysine residues. CD-spectral measurements revealed the overall conformation as well as the immediate heme environment of the hemoprotein to remain unaffected by attachment of the label. Modification caused decreased affinity of p-phenylenediamine and other 4-substituted anilines for the heme site, whereas there was a rise in the extent of substrate interaction. Experiments with pigment containing acetylated lysines gave analogous results, suggesting that the observed phenomenon was due to charge neutralization. There was linear correlation between the Hammett sigma P values and both the optical dissociation constants for arylamine binding to intact enzyme and the dipole moments of the anilines, indicating that basicity along with electronic factors controlled heme liganding; lipophilicity appeared to be of minor importance. Introduction of fluorescein isothiocyanate into the oxygenase was found to influence the bond-making process through modulating basicity of the nitrogenous compounds, but perturbation of optimal spacial orientation of the amine nitrogen toward the heme iron also might have been operative. The lysines studied seem to represent metabolically inactive elements of the substrate channel located on the cytosolic surface of the aggregates, as evidenced by steady-state fluorescence measurements. A hydrophilic segment in the cytochrome P450LM2 molecule that would accommodate the critical residues is discussed.

Mutagenicity of some heterocyclic amines in Salmonella typhimurium with metabolic activation by human red blood cell cytosol

Purified human red blood cell cytosol was used to activate the heterocyclic amines 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ), 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) and 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2) into mutagenic intermediate(s) in the Salmonella test. The liquid preincubation method in the presence of strain TA98 was utilized. In order to understand the mechanism involved in this metabolic activation, some modulators were incorporated in the medium. The results suggest that an oxygenated hemoprotein, probably oxyhemoglobin, is involved in the activation into genotoxic intermediate(s).

Species-specific reaction of liver ultrastructure in Zebrafish (Brachydanio rerio) and trout (Salmo gairdneri) after prolonged exposure to 4-chloroaniline

The morphological alterations of hepatocytes of female zebrafish, Brachydanio rerio, and fingerling rainbow trout, Salmo gairdneri, following prolonged exposure to 0.04, 0.2 and 1 mg/L of 4-chloroaniline were investigated by means of light and electron microscopy. Changes in peroxisomes were visualized by cytochemical demonstration of catalase activity after incubation in the alkaline diaminobenzidine medium. The amount of storage products was illustrated by the silver impregnation technique. In a dose-dependent manner, the reaction of female zebrafish liver is characterized by a disturbance of hepatocytic compartmentation, progressive fenestration and fractionation of the rough endoplasmic reticulum (RER), a decrease in the number of peroxisomes and catalase activity, stratified inclusions in mitochondria, and an augmentation of lysosomes and myelinated bodies. Trout hepatocytes display nuclear inclusions, fractionation and vesiculation of the RER, and an increase in mitochondria, but a decrease of peroxisomes and catalase activity. Whereas glycogen stores are exhausted at 1 mg/L 4-chloroaniline, lipid deposits are amplified. An elevated rate of hepatocytic mitosis as well as the occurrence of glycogen-condensing cells probably derived from hepatocytes indicate the induction of proliferative processes in trout liver. Evaluation and comparison of results with earlier reports suggest that despite the unspecificity of some alterations the combination of pathological symptoms yields a syndrome specific of the species and the substance studied. As a consequence, histological and cytological investigations are recommended as a routine supplement in an integrated test schedule for the assessment of sublethal effects of pollutants in the aquatic environment.

In vitro metabolism of azasqualene derivatives and their effects on aminopyrine N-demethylase activity in rat liver microsomes

The metabolism of squalene dimethylamine (I), a potent inhibitor of 2,3-oxidosqualene (SO) cyclase, and of sixteen other squalene derivatives was investigated in rat liver microsomes. N-oxidation was the only metabolic pathway observed, squalene dimethylamine N-oxide being the only metabolite isolated from incubation of I. The azasqualane and quaternary ammonium derivatives did not form N-oxides during their metabolism. The inhibition of aminopyrine N-demethylase activity was also studied and the IC50, for compound I, which shows weak competitive inhibition, was determined. At 1 mM concentration the other squalene derivatives showed a range of inhibition activity possibly due to their different lipophilicity.

Mechanism of neurotoxic action of beta,beta'-iminodipropionitrile (IDPN): N-hydroxylation enhances neurotoxic potency

The molecular mechanism(s) whereby beta, beta'-iminodipropionitrile (IDPN) induces an excitatory behavioral syndrome and a distinct alteration of the axonal cytoskeleton in experimental animals is not known. We demonstrate here that upon intraperitoneal administration to rats, the N-hydroxy analog of IDPN (HOIDPN) induces a parallel spectrum of both neurotoxic effects of IDPN and is approximately 8 times more potent than IDPN in this regard. This is consistent with the involvement of a flavin monooxygenase-mediated N-oxygenation pathway in the toxic activation of IDPN.

Metabolic N-oxygenation of 2,4-diamino-6-substituted pyrimidines

Biological oxidation of 2,4-diamino-6-substituted pyrimidines have been studied using hepatic microsomes from various mammalian species. The nature of the enzyme(s) involved in the oxidation has been elucidated using various enzyme inhibitors and inducing agents. The 3-N-oxides were formed with 6-piperidino-, 6-diethylamino-, 6-methyl-, and 6-chloro-substituted 2,4-diaminopyrimidines: no evidence of 1-N-oxide formation was obtained. With the 6-hydroxy-, 6-amino-, and unsubstituted 2,4-diaminopyrimidines and melamine, no N-oxidative metabolite was detected. The differences in N-oxide formation was discussed in terms of the effect of substituents on tautomerism and electron distribution. The N-oxygenation was mediated via a cytochrome P450 dependent system.

N-Oxidation of 4-chloroaniline by prostaglandin synthase. Redox cycling of radical intermediate(s)

4-Chloroaniline undergoes N-oxidation in ram seminal-vesicle microsomal preparations supplemented with arachidonic acid to yield N-(4-chlorophenyl)-hydroxylamine and 1-chloro-4-nitrosobenzene. H2O2 also supports metabolism of the amine substrate to the same organic-solvent-extractable products, suggesting that the hydroperoxidase activity of prostaglandin synthase is responsible for the co-oxidation. Analysis of the reaction mixtures by e.s.r. spectrometry reveals the formation of a radical intermediate bearing the characteristics of a strongly immobilized nitroxide. Arylamine-stimulated O2.- release can be observed when the arachidonic acid-containing incubation media are supplemented with NADPH. Redox cycling of the nitroxide/hydroxylamine couple is presumed to represent the major source of O2.-, but additional mechanisms, such as redox changes of nitro anion radicals resulting from potential further metabolism of 1-chloro-4-nitrosobenzene, cannot be excluded. The concerted action of carrier-bound nitroxides and O2.- in initiating damage of cellular macromolecules is discussed.

The role of lipid peroxidation in the N-oxidation of 4-chloroaniline

Irradiation with u.v. light of aerobic aqueous media containing both rabbit liver microsomal fraction and 4-chloroaniline results in N-oxidation of the arylamine. The reaction is severely blocked by exhaustive extraction with organic solvents of the microsomal membranes to remove lipids. Further, scavengers of OH. and O2.-impair the photochemical process. These findings suggest that the observed phenomenon may be closely associated with light-induced lipid peroxidation. Indeed, N-oxidation of 4-chloroaniline is fully preserved when either phospholipid liposomes or dispersed linoleic acid substitute for intact microsomal fraction. Co-oxidation of the amine substrate occurs during iron/ascorbate-promoted lipid peroxidation also, but H2O2 or free OH. radicals do not appear to be involved. Cumene hydroperoxide-sustained rabbit liver microsomal turnover of the amine generates N-oxy product via O2-dependent and -independent pathways; propagation of lipid peroxidation is presumed to govern the former route. Lipid hydroperoxides, either exogenously added to rabbit liver microsomal suspensions or enzymically formed from arachidonic acid in ram seminal-vesicle microsomal preparations, support N-oxidation of 4-chloroaniline. The significance, in arylamine activation, of lipid peroxidation in certain extrahepatic tissues exhibiting but low mono-oxygenase activity is discussed.

Primary arylamine oxidation by a flavinhydroperoxide

4a-Hydroperoxy-5-ethyl-3,8,10-trimethylisoalloxazine (FlEtOOH) was prepared as a chemical model for the flavin-containing monooxygenase enzyme of mammalian liver. FlEtOOH was found to oxidize a series of para-substituted primary arylamines to the corresponding arylnitroso compound. The rates of arylamine oxidation were found to correlate with the Hammett substituent constant, sigma, as well as with amine basicity. These results suggest that amine nucleophilicity should be an important determinant of flavin monooxygenase reactivity toward primary arylamines; nevertheless, the enzyme demonstrates considerable substrate preference based on other factors.

Chromatographic characterization of in vitro metabolites of 5-[2-(N,N-dimethylamino)ethoxy]-7-oxo-7H-benzo[c]fluorene

Detection reactions and RF values in thin-layer chromatography on silica gel were studied for the antineoplastic drug Ih (benfluron) and related substances. On incubation of Ih with homogenate fractions of mammalian livers the N-oxide Ii and 5-[2-(N,N-dimethylamino)ethoxy]-7-hydroxy-7 H-benzo[c]fluorene (IIh) were established as products, and 5-[2-(N-methylamino)ethoxy]-7-oxo-7 H-benzo[c]fluorene (Ig), 5-[2-(N-methylamino)ethoxy]-7-hydroxy-7 H-benzo[c]fluorene (IIg) and a phenolic product of benfluron (IV) were tentatively identified.

The metabolism of 3-benzoylpyridine

3-Benzoylpyridine (3-BP), a decomposition product of the soman antidote, HGG-12 (3-benzoylpyridino(1)-methyl 2'-hydroxyiminomethylpyridino(1')methyl ether dichloride) was rapidly metabolized in the isolated perfused rat liver, giving 3-(alpha-hydroxybenzyl)pyridine and its corresponding glucuronide, 3-benzoylpyridine-N-oxide, and 3-(alpha-hydroxybenzyl)pyridine-N-oxide. The latter is formed both from 3-(alpha-hydroxybenzyl)pyridine and 3-benzoylpyridine-N-oxide. Metabolism of 3-BP studied in rats and dogs in vivo revealed significant species differences. In rat, 80% of 14C-3-BP was excreted as N-oxides and alpha-hydroxybenzyl derivatives in the urine. In dogs, 95% dose was excreted in urine mostly as the glucuronide of 3-(alpha-hydroxybenzyl)pyridine and as the quaternary pyridinium compounds, 3-benzoyl-1-methylpyridinium and 3-(alpha-hydroxybenzyl)-1-methylpyridinium. These latter were hardly detected in rat urine. In contrast to rats, the N-oxides were present only in small amounts in dog urine.

Metabolism of imipramine in vitro: synthesis and characterization of N-hydroxydesmethylimipramine

The synthesis of N-hydroxydesmethylimipramine via the corresponding primary hydroxylamine and oxime is described. The N-oxygenated products are unstable to g.l.c. analysis without prior derivatization; the decomposition products are identified by g.l.c.-mass spectrometry. N-Hydroxydesmethylimipramine is shown to be a metabolite of imipramine and desmethylimipramine on incubation of either with fortified 9000 g liver homogenates of male New Zealand white rabbits. The metabolic product is characterized by mass spectrometry and n.m.r. Didesmethylimipramine is shown to undergo metabolic alpha-C-oxidation, to yield the carboxylic acid, 3-(10,11-dihydro-5H-dibenz[b, f]azepin-5-yl)propionic acid, but not N-oxidation. N-Hydroxydesmethylimipramine is metabolically reduced to desmethylimipramine and metabolized further to 10-hydroxydesmethylimipramine, 2-hydroxydesmethylimipramine and the carboxylic acid. The possible role of N-hydroxydesmethylimipramine and 3-(10,11-dihydro-5H-dibenz[b,f]azepin-5-yl)propionic acid in the formation of iminodibenzyl is discussed.

Comparative studies on the cumene hydroperoxide- and NADPH-supported N-oxidation of 4-chloroaniline by cytochrome P-450

The present study confirms that cytochrome P-450 can act as a catalyst in the cumene hydroperoxide-supported N-oxidation of 4-chloroaniline. Analogous to the NADPH/O2-driven N-oxidation process, product dissociation is likely to limit the overall rate of cytochrome P-450 cycling also in the peroxidatic pathway. The oxy complexes involved in either metabolic route differ with respect to stability, spectral properties and need for thiolate-mediated resonance stabilization. With the organic hydroperoxide, the metabolic profile is shifted from the preponderant production of N-(4-chlorophenyl)hydroxylamine to the formation of 1-chloro-4-nitrobenzene. This finding suggests that the peroxide-sustained N-oxidation mechanism differs in several ways from that functional in the NADPH/O2-dependent oxenoid reaction. Thus one-electron oxidation, triggered by homolytic cleavage of the oxygen donor, is proposed as the mechanism of peroxidatic transformation of 4-chloroaniline.

Effect of dietary carrageenan and pectin on the reduction of nitro-compounds by the rat caecal microflora

Rats were fed either a basal purified diet, or that diet supplemented with 50 g/kg pectin or iota carrageenan for 50 days, and caecal microbial nitroreductase activity determined using p-nitrobenzoic acid, p-nitrophenol, 2,4-dinitrotoluene, nitrofurantoin and metronidazole as substrates. Both pectin and carrageenan increased the weight of caecal contents, and pectin also increased the number of bacteria per caecum. In contrast, carrageenan decreased the caecal bacterial population. Pectin significantly increased the rate of reduction of metronidazole and the rate of conversion of p-nitrobenzoic acid to p-aminobenzoic acid, while carrageenan significantly decreased the rate of reduction of every compound studied. The results demonstrate that microbial reduction of the nitro-group may be altered by diet, although the response found with one nitro-compound may differ from that seen with another substrate.

Dinitro and mononitrobenzo(ghi)perylenes and mononitrocoronene are highly mutagenic in the Ames Salmonella assay

Benzo(ghi)perylene (B(ghi))Per, (191-24-2)) and coronene (Cor, (191-07-1)) are major constituents of the polycyclic aromatic hydrocarbons (PAH) found in automobile exhaust and polluted air [eg, Grimmer et al, 1981]. Nitration of these PAH by NO2 and traces of HNO3, which are also formed in automobile exhaust, seems highly probable. To identify the presence of these nitroarenes in environmental samples and to examine their mutagenic potencies we synthesized and characterized nitro derivatives of both PAH. 5-NO2B(ghi)Per (81316-87-2) and 1-NO2Cor (81316-84-9) produced 405 and 340 revertants/nmole respectively in TA98 in the presence of 0.6 mg of microsomal enzymes (S-9) per plate in the Ames test. 5,8-diNO2B(ghi)Per (83292-25-5) and 5,10-diNO2B(ghi)Per (83292-26-6) produced 21,500 and 4,000 revertants/nmole in TA98 without microsomal activation. Mutagenicity for the dinitrobenzo(ghi)perylenes was also high in TA98NR and TA97 but was reduced by 97% in TA98-1,8DNP. There is close similarity in the orientation and distances between reactive sites (nitrenium ion and carbocation) on the dinitrobenzo(ghi)perylenes and 1,6-dinitropyrene (42397-64-8) and 1,8-dinitropyrene (42397-65-9).