Identification of phase I and phase II metabolites of benfluron and dimefluron in rat urine using high-performance liquid chromatography/tandem mass spectrometry

Biotransformation products of two potential antineoplastic agents, benfluron and dimefluron, are characterized using our integrated approach based on the combination of high-performance liquid chromatography (HPLC) separation of phase I and phase II metabolites followed by photodiode-array UV detection and electrospray ionization tandem mass spectrometry (MS/MS). High mass accuracy measurement allows confirmation of an elemental composition and metabolic reactions according to exact mass defects. The combination of different HPLC/MS/MS scans, such as reconstructed ion current chromatograms, constant neutral loss chromatograms or exact mass filtration, helps the unambiguous detection of low abundance metabolites. The arene oxidation, N-oxidation, N-demethylation, O-demethylation, carbonyl reduction, glucuronidation and sulfation are typical mechanisms of the metabolite formation. The interpretation of their tandem mass spectra enables the distinction of demethylation position (N- vs. O-) as well as to differentiate N-oxidation from arene oxidation for both phase I and phase II metabolites. Two metabolic pathways are rather unusual for rat samples, i.e., glucosylation and double glucuronidation. The formation of metabolites that lead to a significant change in the chromophoric system of studied compounds, such as the reduction of carbonyl group in 7H-benzo[c]fluorene-7-one chromophore, is reflected in their UV spectra, which provides valuable complementary information to MS/MS data.     

The kinetics and mechanism of gas-phase N-oxidation of pyridine with hydrogen peroxide

The kinetics of N-monooxidation of 4-vinylpyridine as a π-deficient heteroaromatic compound under the conditions of gas-phase free-radical chain oxidation was studied. The experimental interference kinetic curves of synchronous hydrogen peroxide decomposition and 4-vinylpyridine N-oxidation reactions were obtained. The region of selective N-oxidation was determined and optimum conditions of N-oxide preparation found. The most probable mechanism was suggested. According to this mechanism, a key role in the free-radical N-oxidation of the substrate and its synchronization with the H₂O₂ decomposition reaction was played by HO₂ radicals.     

杂环化合物氮氧化反应研究的新进展

杂环化合物的N-氧化物是一类重要的有机中间体, 也可以直接用作催化剂、炸药等. 综述了杂环化合物N-氧化反应的最新进展, 包括单氮、双氮和多氮杂环化合物的N-氧化反应, 以及在形成N→O基团的同时合成目标产物的反应, 并重点讨论了具有复杂结构的杂环化合物N-氧化反应.     

Correlated hydrogen bonding fluctuations and vibrational cross peaks in N-methyl acetamide: simulation based on a complete electrostatic density functional theory map

The coherent nonlinear response of the entire amide line shapes of N-methyl acetamide to three infrared pulses is simulated using an electrostatic density functional theory map. Positive and negative cross peaks contain signatures of correlations between the fundamentals and the combination state. The amide I-A and I-III cross-peak line shapes indicate positive correlation and anticorrelation of frequency fluctuations, respectively. These can be ascribed to correlated hydrogen bonding at C[double bond]O and N-H sites. The amide I frequency is negatively correlated with the hydrogen bond on carbonyl C[double bond]O, whereas the amide A and III are negatively and positively correlated, respectively, with the hydrogen bond on amide N-H.     

Microwave-assisted rapid photocatalytic degradation of malachite green in TiO2 suspensions: mechanism and pathways

Microwave-assisted photocatalytic (MPC) degradation of malachite green (MG) in aqueous TiO2 suspensions was investigated. A 20 mg/L sample of MG was rapidly and completely decomposed in 3 min with the corresponding TOC removal efficiency of about 85%. To gain insight into the degradation mechanism, both GC-MS and LC-ESI-MS/MS techniques were employed to identify the major intermediates of MG degradation, including N-demethylation intermediates [(p-dimethylaminophenyl)(p-methylaminophenyl)phenylmethylium (DM-PM), (p-methylaminophenyl)(p-methylaminophenyl)phenylmethylium (MM-PM), (p-methylaminophenyl)(p-aminophenyl)phenylmethylium (M-PM)]; a decomposition compound of the conjugated structure (4-dimethylaminobenzophenone (DLBP)); products resulting from the adduct reaction of hydroxyl radical; products of benzene removal; and other open-ring intermediates such as phenol, terephthalic acid, adipic acid, benzoic acid, etc. The possible degradation mechanism of MG included five processes: the N-demethylation process, adduct products of the hydroxyl radical, the breakdown of chromophores such as destruction of the conjugated structure intermediate, removal of benzene, and an open-ring reaction. To the best of our knowledge, it is the first time the whole MG photodegradation processes have been reported.     

Sites of reaction of pilocarpine

Analysis of the sites of reaction of a biologically important compound, pilocarpine, a molecule with imidazole and butyrolactone rings connected by a methylene bridge, has been accomplished in a quadrupole ion trap with the aim of characterizing its structure/reactivity relationships. Ion-molecule reactions of pilocarpine with chemical ionizing agents, dimethyl ether (DME), 2-methoxyethanol, and trimethyl borate (TMB), along with collision-activated dissociation elucidated the reaction sites of pilocarpine and made possible the comparison of structural features that affect sites of reaction. Based on MS/MS experiments, methylation occurs on the imidazole ring upon reactions with CH3OCH2+ or (CH3OCH2CH2OH)H+ ions but methylation occurs on the lactone ring for reactions with (CH3O)2B+ ions. Bracketing experiments with two model compounds, alpha-methyl-gamma-butyrolactone and N-methyl imidazole, show the imidazole ring to have a greater gas-phase basicity and methyl cation affinity than the lactone ring. The contrast of methylation by TMB ions on the lactone ring is explained by initial addition of the dimethoxyborinium ion, (CH3O)2B+, on the imidazole ring with subsequent collisional activation promoting an intramolecular transfer of a methyl group to the lactone ring with concurrent loss of CH3OBO. Semiempirical molecular orbital calculations are undertaken to further address the favored reaction sites.     

Improved cycle sequencing of GC-rich DNA template

Even when DNA sequencing of purified DNA template failed under the optimal condition, it can be generally contributed to high GC content. GC-rich region of template causes a secondary structure to produce shorter readable sequence. To solve this problem, the sequencing reaction was modified by using dimethyl sulfoxide (DMSO). It was found that 5% (v/v) of DMSO in the reaction mixture recovers sequencing signal intensity with reduced frequency of ambiguous bases. When DMSO was added to sequencing reaction of DNA template with normal GC content, it did not show any adverse effect. Sequencing accuracy and unambiguous base frequency were significantly improved at concentration of 2% to 5% (v/v) DMSO in GC-rich DNA template. DMSO has been empirically introduced to enhance the efficiency of PCR in GC-rich templates. However, the underlying mechanism of improved cycle sequencing by DMSO is unknown. Thus, cycle sequencing reaction was remodified with other additives such as N-methyl imidazole, N-methyl2-pyrrolidone, N-methyl-2-pyridone and glycerol, possessing the similar chemical properties as DMSO. Most of methyl nitrogen ring-containing chemicals did not improve sequencing accuracy, whereas only glycerol mimicked the positive effect of DMSO by the same extent. In the present study, we suggest that the treatment of DMSO improve cycle sequencing by the alteration of structural conformation of GC-rich DNA template.     

The reaction of sodium salts of uracils with chlorides of acids of phosphorus. I

The reaction of the sodium salts of 6-methyluracil (I) and 3, 6-di-methyluracil (II) with methyl and ethyl phosphorochloridates and phosphorochloridothioates give the corresponding N-methyl and N-ethyluracils. The reaction of I with dimethyl phosphorochloridothioate has given a phosphorus- containing reaction product the structure of which has not been established.     

Über Chalkogenolate. 158. Reaktion von N-Methylthioformamid mit Kohlenstoffdisulfid 2. Oxydation von N-Methyl-N-thioformyldithiocarbamaten und S-Methylester der N-Methyl-N-thioformyldithiocarbamidsäure

On Chalcogenolates. 158. Reaction of N-Methyl Thioformamide with Carbon Disulfide. 2. Oxidation of N-Methyl N-Thioformyl Dithiocarbamates and S-Methyl Ester of N-Methyl N-Thioformyl Dithiocarbamic Acid The oxidation of N-methyl N-thioformyl dithiocarbamates with iodine forms the hitherto unknown N-methyl-1,2,4-dithiazole-3,5-dithione . The S-methyl ester of N-methyl N-thioformyl dithiocarbamic acid H? CS? NCH₃? CS? SCH₃ has been prepared by reaction of potassium N-methyl N-thioformyl dithiocarbamate with methyl iodide as well as by reaction of the S-methyl ester of N-methyl N-formyl dithiocarbamic acid with Lawesson reagent. Both compounds have been characterized by means of chemical and diverse spectroscopic methods.     

Molecular electrostatic potentials-II: Mechanistic aspects of electrophilic interactions of some five-membered heterocycles

The interactions of furan, pyrrole and N-methyl pyrrole with electrophiles have been investigated by means of the calculated molecular electrostatic potentials, obtained from INDO wave functions, which indicate the most attractive sites and pathways of attack for an approaching electrophile. The very distinct preference of these heterocycles for α-substitution can be interpreted quite satisfactorily in the case of furan if it is assumed that the α-hydrogen moves out of the plane of the molecule, forming a quasi-tetrahedral carbon, as an initial step in the reaction. For pyrrole and N-methyl pyrrole it is found to be necessary to invoke out-of-plane “bending” of the N-H, N-CH₃ and C_α-H_α bonds to explain both the preference for α-substitution, and also the relative selectivities of furan, pyrrole and N-methyl pyrrole. The energies, atomic charges and bond orders of various forms of these heterocycles are also discussed.     

Platinum-catalyzed multistep reactions of indoles with alkynyl alcohols

PtCl2 effectively catalyzes the multistep reaction of N-methyl indole (1 a) with pent-3-yn-1-ol (2 a) in THF at room temperature for 2 h to give indole derivative 3 a, which contains a five-membered cyclic ether group at C3 in 93% yield. Under similar reaction conditions, various substituted N-methyl indoles 1 b-h and indole (1 i) reacted efficiently with 2 a to afford the corresponding indole derivatives 3 b-h and 3 i in 48-91 and 72% yields. The results showed that N-methyl indoles with electron-donating substituents were more reactive affording higher product yields than those with electron-withdrawing groups. Likewise, various substituted but-3-yn-1-ols 2 b-e and other longer chain alkynyl alcohols 2 f-i also underwent a cyclization-addition reaction with N-methyl indole (1 a) to provide the corresponding cyclization-addition products 3 j-m and 3 a, 3 j, and 3 n-o in good to excellent yields. The present platinum-catalyzed cyclization-addition reaction can be further extended into N-methyl pyrrole. Mechanistically, the catalytic reaction proceeds by an intramolecular hydroalkoxylation of alkynyl alcohol to afford cyclic enol ether followed by the addition of the C--H bond of indole to the unsaturated moiety of cyclic enol ether providing the final product. Experimental evidence to support this proposed mechanism is provided.     

Role of amino acid N-methylation in cyclosporins on ring opening and fragmentation mechanisms during collisionally induced dissociation in an ion trap

The product ion mass spectra (collisionally induced dissociation mass spectra) of 12 different cyclosporins modified at every N-methylated amino acid residue with respect to cyclosporin A were compared and the effect of N-demethylation on ring opening mechanisms was evaluated. The four preferential protonation sites were identified in [MeBmt(1)]-cyclosporins. Three sites represented the N-methylated nitrogens of Sar(3), MeLeu(6) and MeLeu(9), while the remaining one represented the lactone group formed by the intramolecular N,O-acyl shift. Selective N-demethylation resulted either in the deletion of the entire fragment ion series or its substantial attenuation. The structures of three new natural cyclosporins in the study were supported by NMR data.     

A convenient one-pot three component synthesis of 3-aminoalkylated indoles catalyzed by 3-chlorophenylboronic acid

An efficient protocol was developed for the synthesis of 3-aminoalkylated indoles using 3-chlorophenylboronic acid as a catalyst under ambient temperature conditions. The three-component reaction of indoles, aromatic aldehydes and N-methyl aniline offered corresponding 3-aminoalkylated indoles in excellent yields. This protocol presents some remarkable features such as mild reaction conditions, simple workup procedure and excellent yields.     

Simulation of vibrational energy transfer in two-dimensional infrared spectroscopy of amide I and amide II modes in solution

Population transfer between vibrational eigenstates is important for many phenomena in chemistry. In solution, this transfer is induced by fluctuations in molecular conformation as well as in the surrounding solvent. We develop a joint electrostatic density functional theory map that allows us to connect the mixing of and thereby the relaxation between the amide I and amide II modes of the peptide building block N-methyl acetamide. This map enables us to extract a fluctuating vibrational Hamiltonian from molecular dynamics trajectories. The linear absorption spectrum, population transfer, and two-dimensional infrared spectra are then obtained from this Hamiltonian by numerical integration of the Schrodinger equation. We show that the amide I/amide II cross peaks in two-dimensional infrared spectra in principle allow one to follow the vibrational population transfer between these two modes. Our simulations of N-methyl acetamide in heavy water predict an efficient relaxation between the two modes with a time scale of 790 fs. This accounts for most of the relaxation of the amide I band in peptides, which has been observed to take place on a time scale of 450 fs in N-methyl acetamide. We therefore conclude that in polypeptides, energy transfer to the amide II mode offers the main relaxation channel for the amide I vibration.     

Heterodimeric Bis(amino thiol) Complexes of Oxorhenium(V) That Mimic the Structure of Steroid Hormones. Synthesis and Stereochemical Issues

We have prepared a series of bis-bidentate complexes of rhenium that mimic the size, shape, and peripheral functionality of steroidal androgens. In a model system, we used 2D NMR and X-ray crystallographic analysis to show that adjacent N-methyl and oxo substitutents adopt an anti configuration during the coordination reaction. We have synthesized a bis-bidentate oxorhenium(V) complex whose structure and peripheral functionality mimic 5alpha-dihydrotestosterone. 2D-NMR analysis indicates that the N-methyl and oxo substituents are driven into the steroidal anti configuration (beta-N-methyl, alpha-oxo) by the beta-orientation of the methyl group equivalent to C-18. Thus, this metal complex provides a remarkable structural and stereochemical mimic of a steroid. Its in vivo stability, however, appears to be limited.     

A practical total synthesis of hapalosin, a 12-membered cyclic depsipeptide with multidrug resistance-reversing activity, by employing improved segment coupling and macrolactonization

A practical total synthesis of hapalosin, a compound with multidrug resistance-reversing activity, has been carried out using an unprecedented macrolactonization strategy. One of the features of the new approach is the straightforward and fully stereocontrolled access to the key gamma-amino beta-hydroxy carboxylic acid subunit via an efficient acetate aldol addition reaction with N-methyl alpha-aminoaldehydes, which relies on a camphor-derived chiral lithium acetate enolate reagent. The scope of this aldol reaction is investigated and its potential application to the synthesis of other structurally related, biologically relevant compounds illustrated. Remarkably, the chiral tether in the resulting gamma-amino aldol adducts sterically protect the carbonyl group, thus avoiding intramolecular cyclization during the amino group deprotection and the subsequent segment coupling event. After successful segment coupling and smooth, clean release of the chiral auxiliary, a new macrolactonization protocol, based on the principle of double activation of both reactive sites, is applied, which leads to the 12-membered macrolactone hapalosin in unprecedented chemical efficiency.     

Organophotocatalytic N-Demethylation of Oxycodone Using Molecular Oxygen

N-Demethylation of oxycodone is one of the key steps in the synthesis of important opioid antagonists like naloxone or analgesics like nalbuphine. The reaction is typically carried out using stoichiometric amounts of toxic and corrosive reagents. Herein, we present a green and scalable organophotocatalytic procedure that accomplishes the N-demethylation step using molecular oxygen as the terminal oxidant and an organic dye (rose bengal) as an effective photocatalyst. Optimization of the reaction conditions under continuous flow conditions using visible-light irradiation led to an efficient, reliable, and scalable process, producing noroxycodone hydrochloride in high isolated yield and purity after a simple workup.     

Designer drugs 2,5-dimethoxy-4-bromo-amphetamine (DOB) and 2,5-dimethoxy-4-bromo-methamphetamine (MDOB): studies on their metabolism and toxicological detection in rat urine using gas chromatographic/mass spectrometric techniques

Studies are described on the metabolism and the toxicological analysis of the amphetamine-derived designer drug 2,5-dimethoxy-4-bromo-amphetamine (DOB) and its corresponding N-methyl analogue 2,5-dimethoxy-4-bromo-methamphetamine (MDOB) in rat urine using gas chromatographic/mass spectrometric techniques. The identified metabolites indicated that DOB was metabolized by O-demethylation followed by oxidative deamination to the corresponding ketone as well as deamination followed by reduction to the corresponding alcohol. Other metabolic pathways were O,O-bisdemethylation or hydroxylation of the side chain followed by O-demethylation and deamination to the corresponding alcohol. The expected oxo compound after deamination could not be detected. All metabolites carrying hydroxy groups were found to be partly excreted in the conjugated form. MDOB underwent O-demethylation, O,O-bisdemethylation, or hydroxylation of the side chain followed by O-demethylation. Additional N-demethylation to DOB occurred, including the above-mentioned metabolites. Again, all metabolites carrying hydroxy groups were found to be partly excreted in the conjugated form. The authors' systematic toxicological analysis (STA) procedure using full-scan GC/MS after acid hydrolysis, liquid-liquid extraction, and microwave-assisted acetylation allowed the detection of an intake of a dose of DOB and MDOB in rat urine that corresponds to a common drug user's dose. Assuming a similar metabolism, the described STA procedure in human urine should be suitable as proof of an intake of DOB and MDOB.     

Ru(II) complexes of tetradentate ligands related to 2,9-di(pyrid-2'-yl)-1,10-phenanthroline

A series of 1,10-phenanthrolines were prepared having additional ligating substituents at the 2,9-positions. These substituents were either a 4-substituted pyrid-2-yl, quinolin-2-yl, 1,8-naphthyrid-2-yl, N-methyl imidazo-2-yl, or N-methyl benzimidazo-2-yl group. Additionally, 3,6-di-(pyrid-2'-yl)-dipyrido[3,2-a:2',3'-c]phenazine was prepared. All but two of these ligands coordinated Ru(II) in a tetradentate equatorial fashion with two 4-methylpyridines bound in the axial sites. An X-ray structure analysis of the diimidazoyl system indicates considerable distortion from square planar geometry in the equatorial plane. Previously reported variations in the axial ligand for such complexes appear to have a stronger effect on the electronic absorption and redox properties of the system than similar changes in the equatorial ligand. In the presence of excess Ce(IV) as a sacrificial oxidant at pH 1, all the systems examined catalyze the decomposition of water to generate oxygen. Turnover numbers are modest, ranging from 146 to 416.