Browsing by Author "Lopes, Susana M. M."
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- [4+2] Cycloadditions of 3-Tetrazolyl-1,2-diaza-1,3-butadienes: synthesis of 3-Tetrazolyl-1,4,5,6-tetrahydropyridazinesPublication . Lopes, Susana M. M.; Brigas, Amadeu; Palacios, Francisco; Lemos, A.; Melo, Teresa M. V. D. Pinho eThe synthesis of new 3-tetrazolyl-1,4,5,6-tetrahydropyridazines by Diels–Alder reactions of ethyl 3-(tetrazol-5-yl)-1,2- diaza-1,3-butadiene-1-carboxylates is reported. These 1,2- diaza-1,3-dienes reacted with electron-rich heterocycles, nucleophilic olefins and cumulenes, as well as with electrondeficient dienophiles, to give the target compounds regioselectively. Computational studies corroborated the rationalization of the observed reactivity and selectivity.
- Diels–Alder reactions of 3-(1H-tetrazol-5-yl)-nitrosoalkenes: synthesis of functionalized 5-(substituted)-1H-tetrazolesPublication . Lopes, Susana M. M.; Palacios, Francisco; Lemos, A.; Melo, Teresa M. V. D. Pinho eA general route to 1,2-oxazines and open chain oximes bearing a 1H-tetrazolyl substituent via DielseAlder reaction of 3-(tetrazol-5-yl)-nitrosoalkenes is reported. It was also demonstrated that reduction of these adducts followed by deprotection of the tetrazolyl group give 5-(1-aminoalkyl)-1H-tetrazoles, a-amino acid analogues.
- 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.
- A hetero-Diels–Alder approach to functionalized 1H-tetrazoles: synthesis of tetrazolyl-1,2-oxazines, -oximes and 5-(1-aminoalkyl)-1H-tetrazolesPublication . Lopes, Susana M. M.; Lemos, A.; Melo, Teresa M. V. D. Pinho eThis work describes the first and unprecedented examples of inverse electron demand Diels–Alder reactions of 5-(1-nitrosovinyl)-1-phenyl-1H-tetrazole, generated in situ from the corresponding bromooxime, with electron rich alkenes and heterocycles, providing in good overall yields tetrazolyl- 1,2-oxazines and -oximes. Upon subsequent reduction these allowed the access to 5-(1-aminoalkyl)- 1H-tetrazoles, paving the way for a new entry into this important class of compounds, bioisosteres of a-amino acids.
- A hetero-Diels-Alder approach to functionalized 1H-tetrazoles: synthesis of tetrazolyl-1,2-oxazines, -oximes and 5-(1-aminoalkyl)-1H-tetrazolesPublication . Lopes, Susana M. M.; Lemos, A.; Melo, Teresa M. V. D. Pinho eThis work describes the first and unprecedented examples of inverse electron demand Diels–Alder reactions of 5-(1-nitrosovinyl)-1-phenyl-1H-tetrazole, generated in situ from the corresponding bromooxime, with electron rich alkenes and heterocycles, providing in good overall yields tetrazolyl-1,2-oxazines and -oximes. Upon subsequent reduction these allowed the access to 5-(1-aminoalkyl)-1H-tetrazoles, paving the way for a new entry into this important class of compounds, bioisosteres of a-amino acids.
- 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.
- 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.