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An analysis of the 1H, 13C, and 15N NMR substituent chemical shifts (SCSs) of the title compounds in CDCl3 solution has been carried out by using the SCSs of other classes of compounds (arenes, methyl esters or amides), Hammett substituent constants or kinetic data. The results obtained provide information concerning the ground-state electronic distribution of the compounds examined. The results relevant to the carbon and nitrogen atoms of the 1,2,4-oxadiazole ring can be considered of special interest, as the effects of the substit- Introduction For several years our research group has been involved in the use of NMR spectroscopic data (1H, 13C, 15N, and 17O) to obtain information about the ground-state electronic distribution of different classes of organic compounds and to evaluate the influence of substituents on this distribution in order to correlate NMR and reactivity data.[1,2] Thus, the study of the SCSs (substituent-induced chemical shifts) of aryl (or heteroaryl) carboxylic acids[1a–1c] and their derivatives (esters[1d–1g] and amides[1f]) or ketones,[1d,1i] arylhydrazines[2a–2c] or (Z)-arylhydrazones of 3-benzoyl-5- phenyl-1,2,4-oxadiazole[2d] by using both the one- and the two-parameter [DSP (dual substituent parameter)] treatment, has furnished free-energy relationships (FERs) that are useful for an analysis of substituent effects. At the same time, we have deeply investigated the mechanisms of the “monocyclic rearrangement of heterocycles” (MRH or Boulton–Katritzky reaction, BKR)[3] by collect- [a] Dipartimento di Chimica Organica “A. Mangini”, Università di Bologna, Via San Giacomo 11, 40126 Bologna, Italy Fax: + 39-051-209-5688 E-mail: domenico.spinelli@unibo.it [b] Dipartimento di Chimica e Tecnologie Farmaceutiche, Università di Palermo, Via Archirafi 32, 90123 Palermo, Italy [c] Dipartimento di Chimica Organica “E. Paternò”, Università di Palermo, Viale delle Scienze, Parco d’Orleans II, 90128 Palermo, Italy © 2005 Wiley-VCH Verlag GmbH & Co. 3980 KGaA, Weinheim DOI: 10.1002/ejoc.200500236 Eur. J. Org. Chem. 2005, 3980–3986 uents on the chemical shifts of N-4 and C-5 appear in line with kinetic results collected in the study of the rearrangement (Boulton–Katritzky reaction) of the title compounds into the relevant 1,2,3-triazoles, thereby strongly supporting the importance of the leaving-group ability of the N-4/C-5/O-1 system.

The title reaction, carried out in DMF in the presence of triethylamine or potassium carbonate, has furnished the ‘expected’ 3-amino-2-nitrobenzo[ b ]thiophenes 2 o together with the ‘unexpected’ 2-amino-3-nitrobenzo[ b ]thiophenes 3 o , thus recalling the situation observed with other weak nucleophiles in the presence of non-nucleophilic bases. The effects (electronic as well as steric) of the ortho -substituent (OH, NH 2 , OMe, Me, Et, F, Cl and Br) on the course of the reaction have been investigated, determining their influence on yields and product ratios ( 2 o / 3 o ). An analysis of 13 C NMR and MS spectra of 2 o and 3 o has been carried out. Ab initio computations on 2 o f , 2 o i , 3 o f and 3 o i at DFT level have furnished informations on their geometry and stability in the gas phase, thus allowing to assign a role to their stability on the course of the reaction as well as on some EI-MS results.

The reactivity of 3-bromo-2-nitrobenzo[b]thiophene (1) with several (anionic and neutral) nucleophiles has been examined. Only with neutral, weak nucleophiles (as anilines) 1 gives, in the presence of non-nucleophilic bases (triethylamine or potassium carbonate), together with the ‘expected’ 3-amino-2-nitrobenzo[b]thiophenes (3) also the ‘unexpected’ 2-amino-3-nitrobenzo[b]thiophenes (4). The composition of the final isomeric mixture depends on the base added (nature and quantity) and on the solvent used. The results demonstrate the relevance of base-catalysis and support a reaction pathway involving the formation of an anionic intermediate (B) which undergoes addition of a second molecule of nucleophile to give (C) in which migration of the nitro group occurs through a three membered ring (D or E) formed by loss of bromide ion.

The electronic effect of some meta- or para-substituents on the reduction of the title compounds has been investigated. The reversible reduction potential values of these compounds have been evaluated by cyclic voltammetry at a mercury electrode in 0.1 M tetraethylammoniumtetrafluoroborate, dimethylsulfoxide solutions. The substituent effect depends on both its nature and its position. The reduction potential values of the derivatives studied have been correlated with the Hammett substituent constants.

The methoxide-promoted elimination reaction of some 1,1,1-trichloro-2,2-bis(phenyl-substituted)ethanes (1) was investigated. The ortho-substituted derivatives were found to be less reactive than the corresponding ortho-unsubstituted derivatives, irrespective of the nature of their substituent. The reactivity data were correlated with the 13C NMR chemical shift values of C-β of either 1,1,1-trichloro-2,2-bis(phenyl-substituted)ethanes or 1,1-dichloro-2,2-bis(phenyl-substituted)ethenes and the better result was obtained for the former correlation. Activation parameters for the methoxide-promoted elimination of 1 show very similar values for ortho-substituted derivatives. The total data set seems to be more indicative, even if not compelling, of an irreversible E1cB mechanism. Copyright © 2001 John Wiley & Sons, Ltd.

The behaviour of some ortho-alkylhetero-substituted diphenylcarbinols, including deuterium labelled derivatives, under chemical ionisation (methane or isobutane) conditions has been investigated. It has been determined that ortho-alkylhetero diphenylmethyl cations formed by water elimination from the protonated molecule undergo consecutive rearrangements which afford benzyl (or tropylium) ions previously observed for ortho-substituted diphenylcarbenium ions generated by electron ionisation. This reaction also occurs under low-energy collision conditions. Copyright © 2000 John Wiley & Sons, Ltd.

15N and 13C NMR spectra of some ortho-substituted phenylhydrazines were measured at natural isotope abundance in DMSO-d6 solutions. The substituent present exerts a larger effect on the chemical shift of the nitrogen atom directly bound to the aromatic ring (N-1), the second one (N-2) showing an attenuated trend of similar sign. Contrary to what observed for para and meta isomers, the cross-correlation between N-1 and N-2 SCS values of ortho-substituted phenylhydrazines is not satisfactory; on the other hand, N-1 SCSs show a reasonably good linear regression with the σR− constants. As expected, no correlation was found between N-1 and C-1 or H-1 SCS values. Correlations between 13C and 15N chemical shifts of the title compounds with those of ortho-substituted anilines and of monosubstituted benzenes are also reported. Multiparameter regression analysis carried out on a large range of ortho-substituted anilines gave satisfactory results in the TSP treatment of C-1 and C-2 chemical shifts. One-bond 15N–1H coupling constants of ortho-substituted phenylhydrazines and ortho-substituted anilines well correlate with σp− constants.

The 13C NMR chemical shift values of (aryl)(2-nitrobenzo[b]thiophen-3-yl)amines were measured in DMSO-d6 solutions, suggesting the occurrence of an alternate charge polarization at C-3, C-2, C-3a, C-7a, C-4 and C-5. A dual substituent parameter analysis of the experimental data indicates a large or a low resonance contribution for aryl para or meta substituents, respectively, while the inductive component remains constant throughout.

The non-selective methylation of compounds 3a-d using ethereal diazomethane, allowed the synthesis of isomers 4 and 5 which were useful intermediates for the preparation, by a simple approach, of the title compounds 7 and 9. A complete assignment of the chemical shifts to the carbon atoms of the compounds 7 and 9 was performed by different nmr experiments, such as DEPT and XHDEPT for onebond CH correlations and COLOC experiments for long-range C-H correlations.

8,9-Dihydrodipyrazolo[3,4-b:4′,3′-f][1,5]diazocin-10(1H)-ones 7 were prepared by cyclization of 1-ethyl-N,3-dimethyl-4-acetamido-N-(1-R1-3-R2-1H-pyrazol-5-yl)-1H-pyrazole-5-carboxamides 6 by a Bischler-Napieralski cyclization. A complete assignment of the chemical shifts to the carbon atoms of compound 7 was performed by different nmr experiments, such as DEPT and XHDEPT for onebond CH correlations and COLOC experiments for long-range C-H correlations.

5-nitro-3-thiophenecarboxanilide (NTCA3) was clearly mutagenic in Salmonella typhimurium strains TA98, YG1021 (the strain with elevated nitroreductase) and YG1024 (the strain with elevated O-acetyltransferase) and only slightly mutagenic at the gpt locus in AS52 cells. Clastogenic activity in human lymphocytes was dependent on the length of exposure : detectable chromosome aberrations were observed following a 24 h treatment period, but not after 3 h exposure. S9 increased genotoxicity in both mammalian cells and human lymphocytes. Metabolites formed by incubation of NTCA3 with the different cell systems were examined. A time-course study in cell whole extracts showed that bacterial and mammalian cells can acetylate NTCA3 forming 5-acetylamino-3-thiophene-carboxanilide. The formation of this metabolite in human lymphocyte extracts was not confirmed. These data support the conclusions that : (i) both bacterial and mammalian activation pathways play a role in mutations by NTCA3 ; (ii) the N-acetylated derivative is generated by acyltransferase after reduction and is the end product of the metabolism in both bacterial and mammalian cells ; and (iii) different levels of reductase and acetyltransferase activity may contribute to the differential sensitivity of the different cellular species to the genotoxicity of NTCA3. The fact that NTCA3 serves as substrate for enzymatic activities of importance also in human metabolism needs consideration in assessing the potential risk posed by NTCAs.

3-Bromo-2-nitrobenzo[b]thiophene reacted with some amines in N,N-dimethylformamide giving, together with the expected N-substituted 3-amino-2-nitrobenzo[b]thiophenes 3 deriving from aromatic nucleophilic substitution, their isomers 4, whose unexpected structure of N-substituted 2-amino-3-nitrobenzo[b]thiophenes has been determined by means of spectroscopic techniques. As 2-bromo-3-nitrobenzo[b]thiophene gave tars with nucleophiles, the observed reaction could be of use for the synthesis of 4. Some hypotheses on the mechanism of formation of 3 and 4 are suggested.

8,9-Dihydrodipyrazolo[3,4-b:4′,3′-f][1,5]diazocin-10(1H)-ones 7 were prepared by cyclization of 1-ethyl-N,3-dimethyl-4-acetamido-N-(1-R1-3-R2-1H-pyrazol-5-yl)-1H-pyrazole-5-carboxamides 6 by a Bischler-Napieralski cyclization. A complete assignment of the chemical shifts to the carbon atoms of compound 7 was performed by different nmr experiments, such as DEPT and XHDEPT for onebond CH correlations and COLOC experiments for long-range C-H correlations.

The non-selective methylation of compounds 3a-d using ethereal diazomethane, allowed the synthesis of isomers 4 and 5 which were useful intermediates for the preparation, by a simple approach, of the title compounds 7 and 9. A complete assignment of the chemical shifts to the carbon atoms of the compounds 7 and 9 was performed by different nmr experiments, such as DEPT and XHDEPT for onebond CH correlations and COLOC experiments for long-range C-H correlations.

A new aminoacidic derivative of valproic acid (VPA) has been synthesized and characterized by analytical and spectral data. The rationale for the preparation of such potential antiepileptic agent is based on the observation that chemical combination of the anticonvulsant pharmacophore, VPA with essential aminoacids could afford more effective and less toxic actives. The synthesis, characterization, physico-chemical parameters functional for crossing Blood Brain Barrier of N-valproyl-L-tryptophan (4) are reported. The Log D pH7.4 (0.3) indicates that (4) is adequate to cross biological membranes. Its chemical and enzymatic stability were assessed. The experiments indicate high stability of compound (4) at pH conditions of physiological fluids. Moreover, both in plasma and in cerebral enzymatic environments compound (4) doesnt undergo cleavage after 24 h. The anticonvulsant activity of the new compound was assessed against epileptic burst discharges evoked in vitro in rat hippocampal slices (Seizure like events - SLEs) and compared with that of the widely used VPA. Compound (4), even at the lower tested concentration, when compared to VPA, showed an improved protective effect against hippocampal seizures. The collected data suggest that compound (4) could be considered a very valuable candidate for subsequent in vivo evaluation as new potential antiepileptic drug.

The hydrogen-carbon, carbon-carbon double rearrangement, responsible for the formation of benzyl or tropylium ions previously observed in the electron ionization mass spectra of several substituted 1,1-bis(dimethoxydiphenyl)methanes bearing an ortho methoxy group, also occurs for 2-methoxydiphenylmethane (1) itself, the simplest compound of the series. It was shown using deuterium and 13 C labelled 2-methoxydiphenylmethanes (2, 3) that in this instance benzyl or tropilium ions are also formed through two alternative fragmentation routes

Dopamine delivery to the central nervous system (CNS) undergoes the permeability limitations of blood-brain barrier (BBB) which is a selective interface that excludes most water-soluble molecules from entering the brain. Neutral amino acids permeate the BBB by specific transport systems. Condensation of dopamine with neutral amino acids could afford potential prodrugs able to interact with the BBB endogenous transporters and easily enter the brain. The synthesis and characterization of the dopamine derivative 2-amino-N-[2-(3,4-dihydroxy-phenyl)-ethyl]-3-phenyl-propionamide (7) is described. The chemical and enzymatic stability of 7 was evaluated. The molecular weight (300 Da) and Log Papp (0.76) indicated that the physico-chemical characteristics of compound 7 are adequate to cross biological membranes. Compound 7 was enzymatically cleaved to free dopamine in rat brain homogenate (t1/2 = 460 min). In human plasma, the t1/2 of 7 was estimated comparable to that reported for L-DOPA. In view of a possible oral administration of 7, studies of its chemical behavior under conditions simulating those of the gastrointestinal tract showed that no dopamine production occurred; furthermore, 7 is able to permeate through a simulated intestinal mucosal membrane. The collected data suggest that compound 7 could beconsidered a very valuable candidate for subsequent in vivo evaluation.

The electron impact-induced fragmentations of 23 9,10-disubstituted 2,3,6,7-tetraalkoxy-9,10-dihydroanthracenes, including six stereoisomeric pairs, were studied. The loss of the 9-(or 10-)substituent constitutes the main fragmentation route. The resulting ions give rise to a remarkable violation of the so-called even-electron rule as they eject the second substituent at the 10-(or 9-)position as a radical. The latter aspect was particularly investigated with the aid of low-energy (nominal value 15 eV) and mass-analysed ion kinetic energy spectra

The results of the title reaction have furnished proofs against a rearrangement of the carbon-atom skeleton and for a nitro group shift in the relevant nucleophilic substitution.

New 1,3,4-substituted pyrrolo[3,2-c]quinoline derivatives were synthesised in good yields by oxidative heteroannulation of internal imines starting from easily prepared substituted 5-(2-aminophenyl)pyrroles and commercially available aryl and heteroaryl aldehydes. The reaction occurs as a one-pot process involving an intramolecular acid catalysed reaction.

The mutagenic activity of 17 substituted (aryl)(2-nitrobenzo[b]thiophen-3yl)amines has been evaluated in the Ames test with different isogenic strains of Salmonella typhimurium, that varied in their expression of nitroreductase and O-acetyltransferase. Active derivatives induced frameshift mutations in TA98 strain, and differences in the chemical structure resulted in up to 15-fold changes in mutagenic activity. The non-mutagenic compounds are the unsubstituted parent compound and derivatives with para-chloro, para-fluoro, para-diethylamino, meta-bromo and para-dimethylamino groups. They do not show any activity even in strains with higher level of nitroreductase or O-acetyltransferase. The addition of S9 fraction decreases the mutagenic potential or gives comparable results to those obtained without metabolic activation. For electron-donating substituents, the meta-isomers display the greatest mutagenic potency, whereas the transfer of the group to the para-position leads to less active or unactive molecules. All active nitrobenzothiophenes are substrates for bacterial nitroreductase and O-acetyltransferase, as shown by the reduced mutagenicity in the deficient strains and increased mutagenicity in the corresponding overproducing bacteria. Previous reports have pointed out interest in nitrothiophene analogues with para-chloro and para-fluoro substituents as promising anti-inflammatory drugs. The present study further enhances the putative interest in these derivatives, based on absence of mutagenicity.

3-Bromo-2-nitrobenzo[b]thiophene reacted with some amines in N,N-dimethylformamide giving, together with the expected N-substituted 3-amino-2-nitrobenzo[b]thiophenes 3 deriving from aromatic nucleophilic substitution, their isomers 4, whose unexpected structure of N-substituted 2-amino-3-nitrobenzo[b]thiophenes has been determined by means of spectroscopic techniques. As 2-bromo-3-nitrobenzo[b]thiophene gave tars with nucleophiles, the observed reaction could be of use for the synthesis of 4. Some hypotheses on the mechanism of formation of 3 and 4 are suggested.

The mutagenic activity of 23 5-nitro-3-thiophenecarboxanilides and of 5-nitro-3-thiophenecarboxamide, the prototype, (NTCAs) have been evaluated in the Ames test on Salmonella typhimurium strains TA100 ad TA98 with and without metabolic activation. Effects of different substituents (electron-donating and electron-withdrawing) were studied to evaluate structural features that affect the metabolism and the bacterial mutagenic potency. All the derivatives were direct-acting mutagens, the mutagenic potency ranging from 0.7 to 142 revertants (rev.)/nmol in TA100 and from 0.09 to 68 rev./nmol in TA98 strain. Results obtained with strains TA98NR and TA98/1,8-DNP 6 indicated that the mutagenic activity was largely dependent on bacterial nitroreductase, whereas the O-acetylation step was not critical for mutagenic potency. Superoxide (O 2 −• ) and hydroxyl (OH • ) scavengers as well as other radical scavengers and enzymes inhibited NTCAs mutagenicity to different extents. In particular, O 2 −• seemed to be involved in NTCAs mutagenicity, showing a free radical pathway for NTCA metabolism. [ 1 H]- and [ 13 C]NMR data indicated that the effects of different substituents on genotoxicity are probably not exerted on the electron density distribution. The importance of factors such as extent of nitration, reduction potential, orientation of nitrosubstituent and planarity of the molecule are discussed.

The condensation reaction under acid condition of the benzylic alcohols 1, 2 and 3 with the hexadeutero dimethoxybenzenes 4, 5 and 6 leads to the expected hexadeutero bis(dimethoxyphenyl)-2-methylpropanes 7, 8 and 9, respectively. However, the presence of both dodecadeutero and unlabelled 1-bis(2, 4-dimethoxyphenyl)-2-methylpropanes 10 and 11 indicates that 9 undergoes a rapid degenerate dealkylation-alkylation reaction.

A double rearrangement (hydrogen migration followed by carbon–carbon displacement) constitutes the main fragmentation process of the 2-methoxydiphenylmethyl cations formed by benzylic cleavage of the molecular ion of ortho-methoxy-substituted 1,1diphenylalkanes with a wide range of internal energy. This has been demonstrated by recording mass analysed ion kinetic energy (MIKE) spectra, calculation of approximate activation energies (obtained by appearance energy difference) and calculation of a degrees-of-freedom effect. A geometry of the transition state, which accounts for the observed substituent effects, is proposed .

Diphenylmethyl cations formed by benzylic cleavage of the molecular ions of ortho heteroalkyl substituted 1,1-diphenylalkanes undergo the double rearrangement process (H to C followed by C to C) previously reported for ortho-methoxy derivatives. Hence the formation of substituted benzyl (or tropylium) ions allowing this double rearrangement process constitutes an interesting type of fragmentation reaction characteristic for 1,1-diphenylalkanes bearing ortho substituents (OMe, OEt, OiPr, SMe, NHMe, NMe2) which are able to transfer a hydride to the charged benzyl carbon of diphenylmethyl cations formed by benzylic cleavage of the molecular ion.

Les acides formyl-4- et -5 thiophenecarboxyliques-2 donnent des acetals dans le methanol; etude cinetique UV, calcul des constantes de substituants

The effect of phenyl groups on the oxidation of 2,4,5-triphenylpyrrole (I) has been investigated. By oxidation of 2,4,5-triphenylpyrrolemagnesium bromide (II) with oxygen and of 2,4,5-triphenylpyrrole (I) with potassium permanganate besides 2,4,5,2′,4′,5′-hexaphenyl-3,3′-bi-pyrrole (III) another product, which has been assigned the 1,6-dihydro-2,3,4,5,6a-pentaphenylbenzo[g]pyrrole[3,2-e]indole (IV) structure, was obtained. The behaviour of IV toward further oxidation and the spectroscopic data (ir, nmr, ms) were in good agreement with the assigned structures.

The behaviour of 2,4,5-triphenylpyrrole and 2-(p-tolyl)-4,5-diphenylpyrrole under oxidation conditions with dichromate has been investigated. The several reaction products obtained were separated by column cliromatography. In addition to products previously obtained using other oxidizing agents (2), additional products were isolated, namely, the 2,3′-dimers IIIa.b and related oxygenated products Va,b and VIa,b. Their structures were assigned by means of elemental analyses, chemical behaviour and spectroscopic data (ir, uv, nmr andms).

The analysis of the 13C NMR spectra of several 2,3,6,7-tetraalkoxy-9,10-dihalomethyl-9,10-dihydroanthracenes showed a strong dependence of the chemical shift values on the orientation of the halomethyl groups. On this basis it was possible to determine both the configuration (cis or trans) and conformation of the isomers, even if only one isomer was available.

Two new natural substances containing a cyclobutane unit, cardopatine and isocardopatine, the trans and cis isomers respectively of 5,5″ (cyclobut-1,2-ylene-diethynylene)bis 2,2′-bithiophene), together with the known α-terthienyl and 5-(but-3-en-1-ynyl)-2,2′-bithienyl, have been isolated from the roots of Cardopatium corymbosum. Evidence is given that the novel cyclobutane substances are not the products of a spontaneous dimerization of a bithienyl monomeric unit. Structure determination and conformational analysis are reported.

1-Ureido-5-methyl-2,3-dicarbethoxypyrrole under acidic conditions afforded different partially hydrolyzed or decarboxylated products. It has been possible to characterize two isomeric monoethyl esters of dicarboxylic acids of 1-ureidopyrroles by proton gated decoupled carbon-13 nmr spectra on the basis of multiplicities of the carbonyl carbons resonances.

A facile and convenient synthesis of the title compounds is described, using as starting materials the 2-nitro-3-aminothieno[2,3-b]pyridines. Mass spectral data of the above mentioned compounds are briefly discussed.

The 13C n.m.r. chemical shifts of the title compounds and of the corresponding anions have been measured in methanol. The observed substituent chemical shifts have been analysed by means of cross-correlations and of single and dual substituent parameter linear free energy relationships. Different results have been obtained for thiophene and benzene derivatives using DSP analysis: for the first ring system the results have been rationalized in terms of separate resonance and inductive contributions of substituent effects (pointing out the occurrence of an apparent reverse polar effect); in contrast the same treatment of the data for the benzene system gave poor results, confirming once again the different proximity effects in six-and five-membered ring derivatives.

The addition of dimethyl acetylenedicarboxylate to 3-thioxo-1,2,4-triazin-5-ones afforded in good yield cycloadducts which were characterised by i.r., mass, and 1H and 13C n.m.r. spectroscopy. On the basis of their 13C chemical shifts and C,H coupling constant measurements the products were identified as 6-substituted (Z)-2-(methoxycarbonylmethylene)thiazolo[3,2-b][1,2,4]triazine-3,7-diones.