Browsing by Author "Ferreira, Paula M.T."
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- Antioxidant properties of diarylamines derivatives of benzo[b]thiophenes and amino acidsPublication . Ferreira, Isabel C.F.R.; Queiroz, Maria João R.P.; Barros, Lillian; Abreu, Ana S.; Ferreira, Paula M.T.Free radical formation is associated with the normal natural metabolism of aerobic cells. The oxygen consumption inherent to cell growth leads to the generation of a series of oxygen free radicals. The interaction of these species with lipid molecules produces new radicals that may interact with biological systems in a cytotoxic manner. Free radicals and their uncontrolled production are responsible for several pathological processes, such as certain tumours (prostate and colon cancers) the reducing properties of diarylamines make them very important as antioxidants, especially as radical scavengers.
- Synthesis of pure stereoisomers of benzo[b]thienyl dehydrophenylalanines by Suzuki cross-coupling. Preliminary studies of antimicrobial activityPublication . Abreu, Ana S.; Ferreira, Paula M.T.; Monteiro, Luís S.; Ferreira, Isabel C.F.R.; Calhelha, Ricardo C.; Estevinho, Leticia M.Several benzo[b]thienyldehydrophenylalanines were synthesized from pure stereoisomers of the methyl ester of N-(tertbutoxycarbonyl)- b-bromodehydrophenylalanine as an extension of our previously reported method for the synthesis of dehydrotryptophan analogues to dehydrophenylalanine derivatives. The latter were obtained in high yields by N-deprotection and bromination of N,N-bis-(tertbutoxycarbonyl)-( Z)-dehydrophenylalanine using TFA and NBS. This was carried out in two steps or in a one pot procedure resulting in different E/Z ratios. These compounds were coupled under Suzuki cross-coupling conditions [Pd(PPh3)4, Na2CO3, DME/H2O] with several boronic benzo[b]thienyl acids in good to high yields maintaining the stereochemistry of the starting materials. The best yields were obtained when the boronic acid was in position 7 of the benzo[b]thiophene and with the E isomer of the brominated dehydrophenylalanine. In some cases it was possible to increase the lower yields by changing the Pd source to PdCl2(PPh3)2. A model dipeptide was prepared coupling a benzo[b]thienyldehydrophenylalanine with the methyl ester of alanine. Preliminary antimicrobial studies were performed with both isomers of one of the b, b-diaryldehydroalanines obtained. The results show that the compounds are selective and very active (very low MICs) against Gram positive bacteria (B. cereus and B. subtilis) the Z-isomer being more active. The compounds are also active against Candida albicans presenting similar MICs.
- Synthesis of β-benzo[b]thienyldehydrophenylalanine derivatives by one-pot palladium-catalyzed borylation and suzuki coupling (BSC) and metal-assisted intramolecular cyclization: studies of fluorescence and antimicrobial activityPublication . Abreu, Ana S.; Ferreira, Paula M.T.; Queiroz, Maria João R.P.; Ferreira, Isabel C.F.R.; Calhelha, Ricardo C.; Estevinho, Leticia M.Palladium-catalyzed borylation and Suzuki coupling (BSC) in a one-pot procedure was successfully applied to the synthesis of several β-substituted dehydrophenylalanines in the benzo[b]thiophene series, with the stereochemistry of the starting materials being maintained. Bromobenzo[b]thiophenes bearing an ortho EDG (OMe or Me) were used as the components to be borylated with pinacolborane, whilst pure stereoisomers of β-bromodehydrophenylalanines were used as the other Suzuki coupling components. Treatment of the obtained methyl ester of (Z)-N-(tert-butoxycarbonyl)-β- (2,3,5-trimethylbenzo[b]thien-6-yl)dehydrophenylalanine with Pd(OAc)2 and Cu(OAc)2 in DMF at 160 °C gave two in dole derivatives (1:3), the major product resulting from isomerization and cyclization and the minor product resulting from direct cyclization (thienoindole). Carrying out the reaction at 100 °C gave the same products in similar amounts. Use of the methyl ester of (Z)-N-(tert-butoxycarbonyl)-β- (2,3,7-trimethylbenzo[b]thien-6-yl)dehydrophenylalanine as starting material gave only one product, resulting from isomerization and cyclization at 100 °C. Two of the cyclized compounds were subjected to fluorescence studies; the thienoindole could be useful as a fluorescent probe. Preliminary studies of antimicrobial activity were performed on the precursors and on the cyclized products.