Stereospecific (5) JHortho,OMe couplings in methoxyindoles, methoxycoumarins, and methoxyflavones.

Long-range coupling constants (5) JHortho,OMe were measured in series of methoxyindoles, methoxycoumarins, and methoxyflavones by the modified J doubling in the frequency domain method. The COSY and NOESY spectra revealed the coupling of the -OMe group with a specific proton at the ortho position and its preferred conformation. Homonuclear (1) H-(1) H couplings were confirmed by irradiation of the -OMe signal. Density functional theory calculations of (5) JHortho,OMe using the modified aug-cc-pVTZ basis set evidenced that the Fermi contact term shows good agreement with the experimental J values. Accurate chemical shift and coupling constant values followed after iterative quantum mechanical spectral analysis using the PERCH software.

Deuterium-induced isotope effects on the 13C chemical shifts of α-D-glucose pentaacetate.

1,2,3,4,6-Penta-O-acetyl-α-D-glucopyranose and the corresponding [1-(2)H], [2-(2)H], [3-(2)H], [4-(2)H], [5-(2)H], and [6,6-(2)H(2)]-labeled compounds were prepared for measuring deuterium/hydrogen-induced effects on (13)C chemical shift (n)Δ (DHIECS) values. A conformational analysis of the nondeuterated compound was achieved using density functional theory (DFT) molecular models that allowed calculation of several structural properties as well as Boltzmann-averaged (13)C NMR chemical shifts by using the gauge-including atomic orbital method. It was found that the DFT-calculated C-H bond lengths correlate with (1)Δ DHIECS.

Preparation of O-methyl substituted 2-oxofuro- and 2-oxopyrrolidinoindolines by reductive lactonization of oxindol-3-ylacetic acids.

A practical procedure for the preparation of O-methyl substituted 3a,8-dialkyl-2-oxofuroindolines is described. Reductive lactonization of the corresponding oxindol-3-ylacetic acids provides a route for the formation of this class of compounds. Further transformation of 2-oxofuroindolines into 2-oxopyrrolidinoindolines, and then to pyrrolidinoindolines demonstrates their versatility as key intermediates in natural products synthesis. The results of single-crystal X-ray crystallographic analyses are given for five of the studied compounds.

A novel fluorinated stilbene exerts hepatoprotective properties in CCl(4)-induced acute liver damage.

There has been a recently increase in the development of novel stilbene-based compounds with in vitro anti-inflamatory properties. For this study, we synthesized and evaluated the anti-inflammatory properties of 2 fluorinated stilbenes on carbon tetrachloride (CCl4)-induced acute liver damage. To achieve this, CCl4 (4 g·kg(-1), per os) was administered to male Wistar rats, followed by either 2-fluoro-4'-methoxystilbene (FME) or 2,3-difluoro-4'-methoxystilbene (DFME) (10 mg·kg(-1), per os). We found that although both of the latter compounds prevented cholestatic damage (γ-glutamyl transpeptidase activity), only DFME showed partial but consistent results in the prevention of necrosis, as assessed by both alanine aminotransferase activity and histological analysis. Since inflammatory responses are mediated by cytokines, mainly tumour necrosis factor α (TNF-α), we used the Western blot technique to determine the action of FME and DFME on the expression level of this cytokine. The observed increase in the level of TNF-α caused by CCl4 administration was only prevented by treatment with DFME, in agreement with our biochemical findings. This result was confirmed by measuring interleukin-6 (IL-6) levels, since the expression of this protein depends on the level of TNF-α. In this case, DFME completely blocked the CCl4-induced increase of IL-6. Our results suggest that DFME possesses greater anti-inflammatory properties in vivo than FME. DFME constitutes a possible therapeutic agent for liver disease and could serve as a template for structure optimization.

C-6 regioselective bromination of methyl indolyl-3-acetate.

An efficient route to natural occurring methyl 6-bromoindolyl-3-acetate 1c from methyl indolyl-3-acetate 3 was achieved in 3 steps and 68% overall yield. Thus, in order to regioselectively brominate 3 at the C6-position, introduction of electron withdrawing substituents at N1 and C8 was affected to give intermediate 4 in 82% yield. Bromination of 4 with 8 equiv of bromine in CCl4 and washings with aqueous Na2SO3 gave 5 in 86% yield, which was N- and C-decarbomethoxylated by treatment with NaCN in DMSO, affording 1c in 97% yield. The regioselectivity of bromination was evidenced by NMR spectroscopy and X- ray diffraction analysis.

Synthesis of pyrrolidinoindolines from 2-(2-oxo-3-indolyl)acetates: scope and limitations.

A series of 1,3a,8-alkylpyrrolidinoindolines have been synthesized. The scope and limitations of the alkylation of starting methyl oxindol-3-acetates are explored employing electron-rich and electron-poor alkylating agents. Hydrolysis and reductive lactonization of the resulting carboxylic gamma-oxindolic acid derivatives proceeds with good yields to afford 2-oxofuroindolines providing ready access to the pyrrolidinoindoline derivatives.

Unimolecular rearrangements of ketene-O,O-acetals and fragmentations occurring in the gas phase.

Gas phase skeletal rearrangements of regioisomeric 3-cyano-2-methoxy-3a-alkylfuro[2,3-b]- and [3,2-b]indoles were evidenced by product ions [M-32](+•), consistent with loss of methanol, on electron ionization in their mass spectra. The rearranged products occurring in gas phase were demonstrated to have elemental composition and fragmentation properties identical to those of authentic samples of 2-indolyl cyanomalonates. Isotopic labeling experiments support the formation mechanism of the [M-32](+•) ion. Additional thermal gas-phase reaction products were characterized by comparison with an authentic sample.

Cascade [1,3]-sigmatropic rearrangements of ketene O,O-acetals: kinetic and DFT level mechanistic studies.

The regioisomeric alpha-cyano ketene-O,O-dialkyl acetals 2a-e and 4a-e, sequential intermediates in the diazomethane induced conversion of indole alpha-cyano-gamma-lactones 1a-e to 2-indolyl cyanomalonates 5a-e, were isolated and characterized. Formation of the steady-state intermediate cycloprop[b]indoles 3a-e was evidenced by means of NMR and confirmed by the X-ray structure of 3c, demonstrating that the formation of 5a-e from 2a-e proceeds through two consecutive and one parallel unimolecular steps, with intermediates 3a-e formed in reversible processes. Evidence that the reversible reactions proceed via [1,3]-rearrangements is presented. The steady-state kinetic approach applied to intermediate 3 allowed a minimal two consecutive step 2 --> 4--> 5 kinetic model, in which the steric bulkiness of the alkyl substituent affects strongly the associated rate constants, k(1) and k(2), inverting the rate-determining step. The solvation effects enhanced the feasibility of these skeletal rearrangements as they stabilized the transition states to a great extent. The experimental determined thermodynamic parameters and DFT calculations suggest that these cascade rearrangements occur through [1,3]-sigmatropic mechanisms, in which asynchronous bond reorganization processes via four membered pseudopericyclic transition states are highly favorable.

DMD mediated formal synthesis of (+/-)-coerulescine.

A highly efficient method for the formal synthesis of the natural product (+/-)-coerulescine 1 from tetrahydro-beta-carboline 3, mediated by dimethyldioxirane (DMD), is described. Compound 15, the N9-demethylated precursor of 1, was prepared from 3 in 4 steps with an overall yield of 95%. The effect of electron withdrawing groups at the N2,N9 atoms of 3 was explored for the oxidative rearrangement step.

Benzylic coupling constants in toluene derivatives by J doubling in the frequency domain and DFT calculations.

The recently modified J doubling in the frequency domain method (MJDFDM) allowed the determination of (4, 5, 6)J(H, CH(3) ) in toluene, a series of 4-mono- and 3,5-disubstituted toluene derivatives, as well as in 4-picoline. The methyl and aromatic signals were subjected to successive deconvolution processes, which at the end led to singlet signals and afforded the corresponding coupling constant values with a high degree of accuracy. Density functional theory calculation of benzylic coupling constants by addition of the Fermi contact, the spin-dipole, the diamagnetic spin-orbit, and the paramagnetic spin-orbit terms revealed good agreement between predicted and measured values when the B3LYP/aug-cc-pVTZ level of theory was used. Evaluation of the substituent effect over the coupling constant was made for all studied compounds and some limitations of the methodology were evidenced.

Synthesis and biological evaluation of (-)- and (+)-debromoflustramine B and its analogues as selective butyrylcholinesterase inhibitors.

A series of pyrrolidinoindolines have been synthesized as debromoflustramine B (4a) analogues for their evaluation as cholinesterase inhibitors. Structure-activity studies of this series revealed the optimum pharmacophoric elements required for activity and resulted in the discovery of selective butyrylcholinesterase inhibitors with micromolar potency. Biological testing demonstrated that (-)-4a was 7500 times more potent than its enantiomer (+)-4b. The most active inhibitor against BChE in the series was demethyldebromoflustramine B (5a), with an IC50 value of 0.26 microM. X-ray crystallography of 15 and docking studies of selected compounds into human BChE (PDB 1POI) are presented. Molecular modeling studies showed that pi-hydrogen bond, classical hydrogen bond, and cation-pi interactions are critical for optimum potency.

Trans-3-phenyl-2-propenoic acid (cinnamic acid) derivatives: structure-activity relationship as hepatoprotective agents.

Among various phenolic compounds, caffeic acid (3,4-dihydroxycinnamic acid) exhibited pharmacological antioxidant, anticancer and antimutagenic activities. The antioxidant properties of phenolic compounds depend on their chemical structure, however, the role of the ethylenic side chain in the radical scavenging activity remains controversial. Thus, the aim of this study consisted to test cinnamic acid and 15 cinnamic acid derivatives in the well known CCl(4)-induced acute liver damage model, which is dependent on oxidative stress mechanisms. Cinnamic acid and 15 cinnamic acid derivatives (50 mg/kg, p.o.) were administered to male Wistar rats intoxicated with CCl(4) (4 g/kg, p.o.). The activities of gamma-glutamyl transpeptidase, alkaline phosphatase and alanine aminotransferase were measured in serum. The lipid peroxidation products were determined in liver. Compounds with a methoxy group at position 3 or 4, or a 3,4-methylenedioxy moiety were the most active ones. Also, we observed that the monosubstituted 3 or 4 hydroxy, or the bulky 3,4 dibenzyloxy substituted compounds showed lower activity. The poorest activity was displayed by disubstituted 3,4-dihydroxy, dimethoxy or diacetyl cinnamic acid derivatives, the ester derived from cinnamic acid with an 8 carbon chain and N-dimethyl substituted compound. Thus, the methoxy substituted group at positions 3 or 4 or the 3,4-methylenedioxy moiety in the caffeic acid derivatives; seem to be the main features required for the hepatoprotection in this model.

Wagner-Meerwein rearrangement of a [3.3.3]- to a [4.3.3]propellane: deuterium tracer and conformational analysis.

Formation of (-)-[4.3.3]propellane 4 from (-)-14-hydroxymodhephene (2) proceeds through a Wagner-Meerwein rearrangement via C3--C4 bond-shift to give a stable intermediate, dimethylcyclohexadienyl cation A, which undergoes deprotonation. Herein, this mechanism was investigated by using a deuterium labeled substrate at the C-14 methylene group of (-)-2, which was incorporated into the C-4 position of (-)-[4.3.3]propellane 4. The stereostructure of (-)-4 was investigated by applying a combination of NMR experimental and theoretical approaches.

Synthesis of bromoindole alkaloids from Laurencia brongniartii.

A regioselective synthesis of N-carbomethoxy-2,3,5-tribromoindole (6) via a sequential one-pot bromination-aromatization-bromination of N-carbomethoxyindoline (2) is described. The process for the transformation of 2 into 6 permitted the isolation of stable reaction intermediates N-carbomethoxy-5-bromoindoline (3), N-carbomethoxy-5-bromoindole (4), and N-carbomethoxy-3,5-dibromoindole (5). Compound 6 was used to complete the total synthesis of the natural products 1b and 1c. In addition, bromination of N-carbomethoxyindole (11) afforded N-carbomethoxy-2,3,6-tribromoindole (13), from which the natural product 1a was synthesized.

Molecular rearrangements of (-)-modhephene and (-)-isocomene to a (-)-triquinane.

The preparation and further rearrangement of (-)-modhephene (1) to a (-)-triquinane 5 has been assessed through acid catalysis. The rearrangement involved protonation, 1,2 sigma-bond and methyl shifts, and deprotonation. Monitored experiments by 1H NMR spectroscopy suggested the intermediate (-)-isocomene (3), which was further evidenced when a sample of natural (-)-3 undergoes acid-catalyzed conversion to the (-)-triquinane 5. In addition, deuterated (-)-modhephene (1-d) labeled stereospecifically at the 14beta geminal methyl group at C4 was synthesized, through the corresponding chiral deuterated primary alcohol, in 5 steps, starting from natural (-)-14-hydroxymodhephene (8), and rearranged under acid catalysis to elucidate the stereochemical factors that control the methyl shift at this position. The final deuterium-labeled (-)-triquinane, 5-d, obtained from [14-(2)H1]-1-d was established to have deuterium in the methyl group at C5 by 13C NMR spectroscopy. This stereoselective methyl migration is in accordance with the molecular orbital demand formulated by the quantum chemical calculations performed in the present study.

Conformational evaluation and detailed 1H and 13C NMR assignments of flavoxate, a urinary tract antispasmodic agent.

1H and 13C NMR chemical shift assignments for the urinary tract antispasmodic flavoxate (1) and flavoxate hydrochloride (2) were obtained from one- and two-dimensional measurements. A Monte Carlo random search using molecular mechanics, followed by geometry optimization of each minimum energy structure employing DFT calculations at the B3LYP/6-31G* level, and a Boltzmann analysis of the total energies, provided accurate molecular models which describe the conformational behavior of flavoxate (1). The electron density surfaces for the global minimum and the second minimum conformers 1a and 1b of this L-type Ca2+ channel inhibitor were calculated. The presence of both conformers in solution was demonstrated in full agreement with 2D NOESY data and NOE difference spectroscopy.

Electron ionization mass spectra of indolenines obtained using sector and ion trap mass spectrometers.

The electron impact (EI)-induced fragmentations of 18 indolenines were studied using both double-focusing and ion trap mass spectrometers. The compounds used in this study were synthesized to provide correlations of characteristic fragment ions with specific structural differences. In 2-hydroxyindolenines the hydroxy group was involved in a major fragmentation process by interacting with the ester side chain to generate an alpha,beta-unsaturated gamma-lactone structure, with concomitant loss of the corresponding alcohol. In contrast, loss of an alkyl radical, derived solely from the 2-alkoxy group, is a major primary decomposition process for 2-alkoxyindolenines. EI-MS analyses using sector and ion trap spectrometers resulted in similar fragmentation patterns.

1H, 13C and 15N NMR assignments of phenazopyridine derivatives.

Phenazopyridine hydrochloride (1), a drug in clinical use for many decades, and some derivatives were studied by one- and two-dimensional (1)H, (13)C and (15)N NMR methodology. The assignments, combined with DFT calculations, reveal that the preferred protonation site of the drug is the pyridine ring nitrogen atom. The chemoselective acetylation of phenazopyridine (2) and its influence on the polarization of the azo nitrogen atoms were evidenced by the (15)N NMR spectra. Molecular calculations of the phenazopyridines 2-4 show that the pyridine and phenyl groups are oriented in an antiperiplanar conformation with intramolecular hydrogen bonding between the N-b atom and the C-2 amino group preserving the E-azo stereochemistry.