Liliana Lamartina

Cardopatine and isocardopatine, two novel cyclobutane substances from Cardopatium corymbosum

Abstract 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.

Influence of nitroreductase and O-acetyltransferase on the mutagenicity of substituted nitrobenzothiophenamines in Salmonella typhimurium

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.

Mechanism of genotoxicity and electron density distribution by NMR of 5-nitro-3-thiophenecarboxamides, a novel group of direct-acting mutagens in Salmonella typhimurium.

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-DNP6 indicated that the mutagenic activity was largely dependent on bacterial nitroreductase, whereas the O-acetylation step was not critical for mutagenic potency. Superoxide (O2-.) and hydroxyl (OH.) scavengers as well as other radical scavengers and enzymes inhibited NTCAs mutagenicity to different extents. In particular, O2-. seemed to be involved in NTCAs mutagenicity, showing a free radical pathway for NTCA metabolism. [1H]- and [13C]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.

On the reaction of 3-bromo-2-nitrobenzo[b]thiophene with some ortho-substituted anilines: an analysis of the products of reaction and of their NMR and MS properties

Abstract 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.

On the reactivity of 3-bromo-2-nitrobenzo[b]thiophene with nucleophiles: elucidation of the base-catalysed mechanism with rearrangement

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.

Studies in organic mass spectrometry. Part 24† Electron ionization mass spectra of some aryl(2‐nitrobenzo[b]thiophen‐3‐yl)amines

The main fragmentation routes of eighteen title compounds and of three 5-chloro derivatives have been investigated with the aid of linked scan (B/E = constant) spectrometry, accurate mass measurements and deuterium labelling. Copyright

A new general fragmentation reaction in mass spectrometry: The hydrogen-carbon, carbon-carbon double rearrangement of 2 heteroalkyl substituted diphenylmethyl cations

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.

NITROGEN-15 NMR STUDIES ON HYDRAZINES : 2-SUBSTITUENT EFFECT ANALYSIS IN ORTHO-SUBSTITUTED PHENYLHYDRAZINES AND ANILINES

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.

An analysis of 13C nuclear magnetic resonance substituent chemical shifts in 3-substituted thiophene-2-carboxylic and 2-substituted benzoic acids by linear free energy relationships

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.

Studies in organic mass spectrometry. Part 25. Benzyl ion formation in chemical ionisation (methane or isobutane) of some ortho‐alkylhetero‐substituted diphenylcarbinols

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.