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Photochemistry of 1-allyl-4-aryltetrazolones in solution; structural effects on...
Ismael, A.; Serpa, C.; Cristiano, Maria Lurdes SantosThe photochemistry of tetrazolones derived from the carbocyclic allylic alcohols cyclohex-2-enol and 3-methylcyclohex-2-enol and from the natural terpene alcohol nerol was investigated in solution with the aim of assessing the effect of solvent and of structural constraints imposed by bulky allylic moieties on photoproduct selectivity and stability. Photolysis of tetrazolones derived from nerol and cyclohex-2-e...
Examination of the cytotoxic and embryotoxic potential and underlying mechanism...
Copple, I. M.; Mercer, A. E.; Firman, J.; Donegan, G.; Herpers, B.; Wong, M. H.; Chadwick, J.; Bringela, A.; Cristiano, Maria Lurdes SantosSemisynthetic artemisinin-based therapies are the first-line treatment for P. falciparum malaria, but next-generation synthetic drug candidates are urgently required to improve availability and respond to the emergence of artemisinin-resistant parasites. Artemisinins are embryotoxic in animal models and induce apoptosis in sensitive mammalian cells. Understanding the cytotoxic propensities of antimalarial drug ...
Sigmatropic rearrangements in 5-allyloxytetrazoles
Frija, L.; Reva, I. D.; Ismael, A.; Coelho, Daniela; Fausto, R.; Cristiano, Maria Lurdes SantosMechanisms of thermal isomerization of allyl tetrazolyl ethers derived from the carbocyclic allylic alcohols cyclohex-2-enol and 3-methylcyclohex-2-enol and from the natural terpene alcohol nerol were investigated. In the process of the syntheses of the three 1-aryl-5-allyloxytetrazoles, their rapid isomerization to the corresponding 1-aryl-4-allyltetrazol-5-ones occurred. The experiments showed that the imidat...
Bond energy/eond order relationships for N-O linkages and a quantitative measur...
Johnstone, Robert A. W.; Loureiro, Rui M. S.; Labat, G.; Cristiano, Maria Lurdes SantosThe nitro group is active in metabolic systems and can be found as an integral part of a number of useful curative drugs and many toxic substances. The basis for much of this activity is not fully understood. It is not necessarily caused directly by through-bond electronic effects but may also be due to direct H-bonding to nitro or to indirect interference by the nitro group with existing H-bonding. An unusual ...
Photochemical Transformations of Tetrazole Derivatives: Applications in Organic...
Frija, L.; Ismael, A.; Cristiano, Maria Lurdes SantosTetrazoles remain a challenge to photochemists. Photolysis leads to cleavage of the tetrazolyl ring, may involve various photodegradation pathways and may produce a diversity of photoproducts, depending on the structure and conformational flexibility of the substituents and the possibility of tautomerism. If the photochemistry of tetrazoles is considered within the frame of synthetic applications the subject is...
Photochemistry of 5-allyloxy-tetrazoles: steady-state and laser flash photolysi...
Frija, L.; Khmelinskii, Igor; Serpa, C.; Reva, I. D.; Fausto, R.; Cristiano, Maria Lurdes SantosThe photochemistry of three 5-allyloxy-tetrazoles, in methanol, acetonitrile and cyclohexane was studied by product analysis and laser flash photolysis. The exclusive primary photochemical process identified was molecular nitrogen elimination, with formation of 1,3-oxazines. These compounds were isolated in reasonable yields by column chromatography on silica gel and were fully characterized. DFT(B3LYP)/6-31G(d...
UV-induced photochemistry of matrix-isolated 1-phenyl-4-allyl-tetrazolone
Frija, L.; Reva, I. D.; Gómez-Zavaglia, A.; Cristiano, Maria Lurdes Santos; Fausto, R.The photochemistry and molecular structure of 1-phenyl-4-allyl-tetrazolone (PAT) was studied by FT-IR matrix isolation spectroscopy and DFT(B3LYP)/6-311++G(d,p) calculations. The spectrum of matrix-isolated PAT monomers agrees well with the sum spectrum of three conformers predicted theoretically. UV irradiation (k > 235 nm) of matrix-isolated PAT induces three types of photofragmentation: (1) production of phe...
Investigations into the mechanism of action of nitrobenzene as a mild dehydroge...
Cristiano, Maria Lurdes Santos; Gago, David J. P.; Gonsalves, Antonio M. d'A. Rocha; Johnstone, Robert A. W.; McCarron, Moya; Varejão, Jorge M. T. B.Protonated nitrobenzene can be used to dehydrogenate a range of hydrocarbons, which already possess at least one double bond. Kinetic and spectroscopic results, together with known electrode potentials, yield approximate limits within which protonated nitrobenzenes can be expected to effect dehydrogenation of hydroaromatic compounds. A high yielding synthesis of benzo[ j ]fluoranthene is described.
Low temperature matrix-isolation and solid state vibrational spectra of 5-chlor...
Bugalho, Susana C. S.; Serra, A. C.; Lapinski, L.; Cristiano, Maria Lurdes Santos; Fausto, R.The vibrational spectra of 5-chlorotetrazole (CN4HCl) isolated in an argon matrix (T ¼ 8.5 K) and in the solid state (at room temperature) were studied. The infrared spectrum of monomers of 5-chlorotetrazole isolated in an argon matrix agrees well with the spectrum predicted theoretically (DFT(B3LYP)/6-31G*) for the 2Htautomer of the compound. The bands assigned to the 1H-tautomer appear in the experimental spe...
Structural effects on sigmatropic shifts in heteroaromatic allyl ethersElectron...
Araújo, Nuna C.; Barroca, Pedro M. M.; Bickley, Jamie F.; Brigas, Amadeu F.; Cristiano, Maria Lurdes Santos; Johnstone, Robert A. W.In contrast to the known thermal, exclusively [3,3], O- to N- rearrangement of allyl groups in phenyltetrazoles (1, Scheme 1), the comparable migration of the allyl group in pseudosaccharyl ethers (3; Scheme 2) has been shown to proceed through both [1,3]- and [3,3]-mechanisms, 4, 5; for the pseudosaccharyl derivative of the natural product myrtenol (6; Scheme 3) only the product 7 of a [1,3]-shift has been obs...
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