Percorrer por autor "Kirsch, Gilbert"
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- Evaluation of the antioxidant properties of diarylamines in the benzo[b]thiophene series by free radical scavenging activity and reducing powerPublication . Ferreira, Isabel C.F.R.; Queiroz, Maria João R.P.; Vilas-Boas, Miguel; Estevinho, Leticia M.; Begouin, Agathe; Kirsch, GilbertThe antioxidant properties of substituted diarylamines in the benzo[b]thiophene series were evaluated by their reducing power and free radical scavenging activity. The results were compared with those of standards: acid ascorbic for the first method and BHA and BHT for the second. For both methods it was possible to establish some structure–activity relationships (SARs) based on the position of the arylamination on the benzo[b]thiophene moiety, the presence of different substituents on the phenyl ring (F, 1 or 2 OMe) and on the thiophene ring (H, CO2Et, CO2H).
- High efficient intramolecular cyclisation of ortho-halodiarylamides or amines to tienocarbazoles and indolobenzo[b]thiophenesPublication . Ferreira, Isabel C.F.R.; Queiroz, Maria João R.P.; Kirsch, Gilbert
- Novel synthetic routes to thienocarbazoles via palladium or copper catalyzed amination or amidation of arylhalides and intramolecular cyclizationPublication . Ferreira, Isabel C.F.R.; Queiroz, Maria João R.P.; Kirsch, GilbertPalladium or copper catalyzed aminations or amidations were performed to obtain diarylamines and diarylacetamides precursors of thienocarbazoles. The fact that an ortho-bromodiarylamine did not cyclize to the corresponding thienocarbazole under conditions known for carbazoles from ortho-halodiphenylamines, conducted us to a highly efficient method of palladium-catalyzed intramolecular cyclization with N-deprotection of ortho-halodiarylacetamides to thienocarbazoles. Other method of intramolecular cyclization of diarylamines based on the reoxidation of the Pd(0) formed by Cu(OAc)2, avoiding the use of stoichiometric amounts of Pd(OAc)2, gave thienocarbazoles in a moderate yield, including a ring A methoxylated compound. An attempt to combine palladium and copper catalyses in a ‘one pot’ reaction of amination and intramolecular cyclization gave as major product a N-benzo[b]thiophene substituted carbazole and the required thienocarbazole in low yield.
- Palladium-catalysed amination of electron-deficient or relatively electron-rich benzo[b]thienyl bromides - Preliminary studies of antimicrobial activity and SARsPublication . Queiroz, Maria João R.P.; Begouin, Agathe; Ferreira, Isabel C.F.R.; Kirsch, Gilbert; Calhelha, Ricardo C.; Barbosa, Sandra; Estevinho, Leticia M.Several diarylamines in the benzo[b]thiophene series were prepared in good to high yields by palladium-catalysed amination of ethyl 3-bromobenzo[b]thiophene-2-carboxylate with anilines and 5-aminoindole in the presence of Pd(OAc)2, BINAP and Cs2CO3 in toluene. The presence of the ester group at the 2-position of the benzo[b]thiophene moiety increases the yields and lowers the heating times relative to the reactions performed with 3-bromobenzo[b]thiophene. When aminopyridines were used instead of anilines, the ligand and the solvent need to be changed to XANTHPHOS and dioxane in the amination reaction. With 2-aminopyridine a onepot C−N coupling and intramolecular cyclization involving the nitrogen atom of the pyridine ring occurred, with loss of ethanol, giving an interesting fluorescent tetracyclic heteroaromatic compound. The antimicrobial activity, the minimal inhibitory concentrations (MICs) and the structure-activity relationships (SARs) were evaluated. A selectivity with low MICs was observed against Bacillus Cereus, and good results were also obtained against Candida albicans. The acids obtained by hydrolysis of the ester group, as non-proteinogenic α,β-unsaturated β-amino acids, can be incorporated into peptide chains to induce conformational constraints.
- Palladium-catalyzed amination and cyclization to heteroannellated indoles and carbazolesPublication . Ferreira, Isabel C.F.R.; Queiroz, Maria João R.P.; Kirsch, GilbertNew ortho-bromodiarylamines in the benzo[b]thiophene series were prepared by palladium-catalyzed amination, either in the benzene or in the thiophene ring. These were submitted to palladium-catalyzed cyclization, under different required conditions, to give several differently substituted thieno[3,2-c] or [2,3-b]carbazoles and indolo[3,2-b]benzo[b]thiophenes. This constitutes a novel synthetic route to both tetracyclic systems
- Palladium-catalyzed amination of electron-rich or poor benzo[b]thienyl bromidesPublication . Begouin, Agathe; Ferreira, Isabel C.F.R.; Queiroz, Maria João R.P.; Kirsch, GilbertRecently we have applied the palladium-catalyzed amination to the synthesis of ortho-bromodiarylamincs in the benzo[blthiophene series . Here we describe the application of this methodology to the amination of electron-rich or poor 3-bromobenzo[b}thiophcnes, using the same conditions for both cases.
- Palladium-catalyzed amination to obtain o-halodiarylamines precursors of thienocarbazolesPublication . Ferreira, Isabel C.F.R.; Queiroz, Maria João R.P.; Kirsch, GilbertWith the aim of obtaining potential anti-tumoural thienocarbazoles by a ring B convergent method of synthesis, o-halodiarylacetamides were prepared by copper assisted C-N coupling from 2-bromo-iodobenzene and 6-acetamido-2,3,5-trimethylbenzo[b]thiophene, prepared from the 6-acetyl compound.
- Palladium-catalyzed cyclisation-deprotection of o-halodiarylacetamides, obtained by C-N copper assisted coupling, to the corresponding 6H-Thieno-[2,3-c]carbazolePublication . Ferreira, Isabel C.F.R.; Queiroz, Maria João R.P.; Kirsch, GilbertWith the aim of obtaining potential anti-tumoural thienocarbazoles by a ring B convergent method of synthesis, o-halodiarylacetamides were prepared by copper assisted C-N coupling' from 2-bromo-iodobenzene and 6-acetamido-2,3,5-trimethylbenzolb]thiophene, prepared from the 6-acetyl compound.
- Synthesis and antimicrobial activity studies of ortho-chlorodiarylamines and heteroaromatic tetracyclic systems in the benzo[b]thiophene seriesPublication . Queiroz, Maria João R.P.; Ferreira, Isabel C.F.R.; Gaetanoa, Yannick; Kirsch, Gilbert; Calhelha, Ricardo C.; Estevinho, Leticia M.ortho-Chlorodiarylamines in the 2,3,7-trimethylbenzo[b]thiophene series were prepared in high yields (70–85%) by C–N palladium-catalyzed cross-coupling using P(t-Bu)3 as ligand and NaOt-Bu as base. A palladium-assisted C–C intramolecular cyclization of the coupling products gave thienocarbazoles and the dechlorinated diarylamines. Studies of antimicrobial activity of the compounds obtained, against representative species of bacteria (Escherichia coli, Pseudomonas aeruginosa, Bacillus cereus and Bacillus subtilis) and fungi (Candida albicans), were performed. We have also included in the biological assays some pyridine derivatives previously prepared by us, and it was possible to establish some structure–activity relationships (SARs).
- Synthesis of 6-(2’ or 4’- nitrophenyl)benzo[b]thiophenes by Palladium-catalyzed cross-couplingPublication . Ferreira, Isabel C.F.R.; Queiroz, Maria João R.P.; Kirsch, GilbertThe palladium-catalyzed cross-coupling reactions of organoboron compounds are very useful for carbon-carbon bond formation. Compounds 1 were synthesized by a palladium-catalyzed cross-coupling of bromo or iodonitrobenzenes with boronic esters 2, which were prepared from methylated 6- bromobenzo[b]thiophenes2 by halogen-metal exchange and transmetalation. The intermediates esters 2 were not isolated but directly, after evaporation of the ether, coupled in acetone/water using palladium acetate in the presence of sodium hydrogencarbonate. Yields of isolated compounds 1 were about 40%.