Browsing by Author "Pinho e Melo, Teresa M. V. D."
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- Asymmetric neber reaction in the Synthesis of Chiral 2-(Tetrazol-5-yl)-2H-AzirinesPublication . Alves, Claudia; Grosso, Carla; Barrulas, Pedro; Paixao, Jose A.; Cardoso, Ana L.; Burke, Anthony J.; Lemos, Americo; Pinho e Melo, Teresa M. V. D.A successful one-pot methodology for the synthesis of chiral 2-tetrazolyl-2H-azirines has been established, resorting to organocatalysis. The protocol involves the in situ tosylation of beta-ketoxime-1H-tetrazoles followed by the Neber reaction, in the presence of chiral organocatalysts. Among the organocatalysts studied a novel thiourea catalyst derived from 6 beta-aminopenicillanic acid afforded excellent enantioselectivities.
- Ethyl 7-Acetyl-8a-methyl-3-(1-phenyl-1H-tetrazol-5-yl)-1,4,4a,5,6,8a-hexahydro-7H-pyrano[2,3-c]pyridazine-1-carboxylatePublication . Lopes, Susana M. M.; Lemos, Americo; Paixão, José A.; Pinho e Melo, Teresa M. V. D.The Diels–Alder reaction of ethyl 3-(1-phenyl-1H-tetrazol-5-yl-1,2-diaza-1,3-butadiene-1-carboxylate with 2-acetyl-6-methyl-2,3-dihydro-4H-pyran (methyl vinyl ketone dimer) regioselectively afforded the corresponding 3-(tetrazol-5-yl)-hexahydro-7H-pyrano[2,3-c]pyridazine in quantitative yield. An X-ray crystal structure of this cycloadduct is reported.
- Natural deep eutectic solvents in the hetero-Diels-Alder approach to bis(indolyl)methanesPublication . Grosso, Carla; Brigas, Amadeu; de los Santos, Jesus M.; Palacios, Francisco; Lemos, Americo; Pinho e Melo, Teresa M. V. D.For the first time, the use of natural deep eutectic solvents (NADES) as reaction media to carry out hetero-Diels-Alder reactions is disclosed. This allowed to improve the efficiency and sustainability of the synthetic approach to bis(indolyl)methanes (BIMs) based on bis-hetero-Diels-Alder/conjugate addition reactions of nitroso- and azoalkenes with indoles. The ternary mixture of H2O with choline chloride/glycerol allowed the tuning of the physical properties of this NADES leading to a better solvent system, affording the target hydroxyiminomethyl- and hydrazonomethyl-BIMs, in much shorter reaction times, higher efficiency and easier isolation procedures. Furthermore, the direct access to carbonyl-BIMs was possible when 3-methyl-1-tert-butoxycarbonyl azoalkenes were used. [GRAPHICS] .
- One-Pot Synthetic Approach to Dipyrromethanes and Bis(indolyl)methanes via Nitrosoalkene ChemistryPublication . Cardoso, Ana L.; Lopes, Susana M. M.; Grosso, Carla; Pineiro, Marta; Lemos, Americo; Pinho e Melo, Teresa M. V. D.A one-pot regio- and stereoselective synthesis of a dipyrromethane and a bis(indolyl)methane based on two consecutive reactions of nitrosoalkenes with pyrrole or indole, respectively, is described as an experiment to be carried out by upper-division undergraduate students in a laboratory classroom. Importantly, the ability of electrophilic conjugated nitrosoalkenes to react via Michael addition or hetero-Diels-Alder reactions with electron-rich heterocycles will provide an opportunity for students to acknowledge alternative reaction pathways underlying certain transformations. Reactions were performed under mild conditions using water as a solvent, followed by purification through column chromatography on silica gel, and characterization of the desired products by NMR and IR spectroscopy. This laboratory experiment combines organic synthesis, determination of the purity of compounds (TLC analysis and melting point measurements), as well as structural analysis (interpretation of 1D NMR spectra). Several important organic chemistry concepts, such as stereo- and regioselectivity, in situ generation and reactivity of conjugated nitrosoalkenes, conjugated 1,4-addition reactions, and cycloaddition reactions, are also discussed.
- Regioselectivity in hetero diels-alder reactionsPublication . Grosso, Carla; Liber, Marta; Brigas, Amadeu; Pinho e Melo, Teresa M. V. D.; Lemos, AmericoRegioselectivity in hetero Diels-Alder reactions can be observed in a simple reaction between a nonsymmetrical heterodiene and an unsymmetrical heterodienophile. A 9 h and easy to implement laboratory experiment is described, in which students can observe the regioselectivity of inverse "electron-demand" hetero Diels-Alder reactions of an azoalkene with furan or 2,3-dihydrofuran acting as dienophile. This experiment combines synthesis, structural analysis (IR spectroscopy and NMR spectroscopy), and dry- and vacuum-flash isolation methods.
- Synthesis and anti-cancer activity of chiral tetrahydropyrazolo[1,5-a] pyridine-fused steroidsPublication . Lopes, Susana M. M.; Sousa, Emanuel P.; Barreira, Luísa; F. Marques, C.; Rodrigues, Maria João; Pinho e Melo, Teresa M. V. D.Regio-and stereoselective synthesis of novel chiral 4,5,6,7-tetrahydropyrazolo [1,5-a]pyridine fused steroids via [8 pi + 2 pi] cycloaddition of diazafulvenium methides with steroidal scaffolds is reported. The biological evaluation of the new family of hexacyclic steroids as anti-cancer agents was also carried out. Hexacyclic steroids bearing a benzyl group at C-22, derived from 16-dehydropregnenolone and 16-dehydroprogesterone, show considerable cytotoxicity against EL4 (murine T-lymphoma) in contrast with the corresponding C-22-unsubstituted derivatives showing low cytotoxicity. Thus, results indicate that the presence of the benzyl group is important to ensure cytotoxicity.