Percorrer por autor "Frija, Luís M. T."
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- In vitro assessment of antimicrobial, antioxidant, and cytotoxic properties of Saccharin-Tetrazolyl and-Thiadiazolyl derivatives: the simple dependence of the pH value on antimicrobial activityPublication . Frija, Luís M. T.; Ntungwe, Epole; Sitarek, Przemysław; Andrade, Joana M.; Toma, Monika; Śliwiński, Tomasz; Cabral, Lília; Cristiano, Maria de Lurdes; Rijo, Patrícia; Pombeiro, Armando J. L.The antimicrobial, antioxidant, and cytotoxic activities of a series of saccharin-tetrazolyl and -thiadiazolyl analogs were examined. The assessment of the antimicrobial properties of the referred-to molecules was completed through an evaluation of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values against Gram-positive and Gram-negative bacteria and yeasts. Scrutiny of the MIC and MBC values of the compounds at pH 4.0, 7.0, and 9.0 against four Gram-positive strains revealed high values for both the MIC and MBC at pH 4.0 (ranging from 0.98 to 125 µg/mL) and moderate values at pH 7.0 and 9.0, exposing strong antimicrobial activities in an acidic medium. An antioxidant activity analysis of the molecules was performed by using the DPPH (2,2-diphenyl-1-picrylhydrazyl) method, which showed high activity for the TSMT (N-(1-methyl-2H-tetrazol-5-yl)-N-(1,1-dioxo-1,2-benzisothiazol-3-yl) amine, 7) derivative (90.29% compared to a butylated hydroxytoluene positive control of 61.96%). Besides, the general toxicity of the saccharin analogs was evaluated in an Artemia salina model, which displayed insignificant toxicity values. In turn, upon an assessment of cell viability, all of the compounds were found to be nontoxic in range concentrations of 0-100 µg/mL in H7PX glioma cells. The tested molecules have inspiring antimicrobial and antioxidant properties that represent potential core structures in the design of new drugs for the treatment of infectious diseases.
- Synthesis and structure of novel pyrimidine‐thioethers: structural effects on reactivity along with an unpredicted dimethylamination reactionPublication . Costa, Inês; Frija, Luís M. T.; Augusto, André; Paixão, José A.; Cristiano, Maria de LurdesBuchwald–Hartwig reactions have been in the spotlight over the past years due to their usefulness in creating a wide range of chemical skeletons applied in drug discovery. Aminopyrimidines are heterocyclic structures with significant biological relevance and compounds bearing the amino- and diaminopyrimidine motifs have been associated with antiviral, antibacterial, antiparasitic, antifungal, anticancer, and anti-inflammatory properties. Given the notable status of aminopyrimidines in the design of target-specific drug candidates, the synthesis and structure of four aminopyrimidine-arylsulfide conjugates (3, 4, 5, and 6) are reported that are designed to inhibit trypanothione reductase, a key enzyme in the redox pathway of trypanosomatids. When applying the Buchwald–Hartwig synthetic approach, the formation of different products is witnessed by altering the reaction conditions, observing that regioselectivity is conditioned by reaction time and by Boc-protection of the starting 2,6-dichloropyrimidin-4-amine. The electron-withdrawing character of the protecting group appears to increase the susceptibility of the pyrimidine at C2 for further reaction with the solvent, DMF, yielding the corresponding diaminopyrimidine-based conjugates. The crystal structures of the novel aminopyrimidine-arylsulfide conjugate and their Boc-protected 2,6-dichloropyrimidin-4-amine precursors are disclosed and discussed.
- Synthesis of Non-symmetrical Dispiro-1,2,4,5-Tetraoxanes and Dispiro-1,2,4-Trioxanes Catalyzed by Silica Sulfuric AcidPublication . Amado, Patrícia; Frija, Luís M. T.; Coelho, Jaime A. S.; O’Neill, Paul M.; Cristiano, Maria De LurdesA novel protocol for the preparation of nonsymmetrical 1,2,4,5-tetraoxanes and 1,2,4-trioxanes, promoted by the heterogeneous silica sulfuric acid (SSA) catalyst, is reported. Different ketones react under mild conditions with gemdihydroperoxides or peroxysilyl alcohols/beta-hydroperoxy alcohols to generate the corresponding endoperoxides in good yields. Our mechanistic proposal, assisted by molecular orbital calculations, at the.B97XD/def2-TZVPP/PCM(DCM)// B3LYP/6-31G(d) level of theory, enhances the role of SSA in the cyclocondensation step. This novel procedure differs from previously reported methods by using readily available and inexpensive reagents, with recyclable properties, thereby establishing a valid alternative approach for the synthesis of new biologically active endoperoxides.
- Unanticipated reactivity toward nucleophilic attack in the synthesis of saccharyl-1,3,4-thiadiazolyl conjugates: structure and mechanistic insightsPublication . Guerreiro, Bruno; Carvalho, Daniel F.; Coelho, Jaime A. S.; Frija, Luís M. T.; Paixão, José A.; Cristiano, Maria de LurdesAlong with the synthetic process optimization of 3- [(5-methyl-1,3,4-thiadiazole-2-yl)sulfanyl]-1,2-benzothiazole 1,1- dioxide (MTSB), a selective copper chelator with potential interest in cancer chemotherapy, the unprecedented isolation of a novel compound, 3-(1,1-dioxidobenzo[d]isothiazol-3-yl)-5-methyl-1,3,4- thiadiazole-2(3H)-thione (BMTT), evidenced an unexpected reactivity of the starting 5-methyl-1,3,4-thiadiazole-2-thiol. To shed light into the reaction mechanisms, quantum chemical calculations were conducted at the M06-2X/def2-TZVPP/PCM- (THF)//M06-2X/6-31++G(d,p) level of theory. The results conjecture the formation of BMTT from nucleophilic attack of the nitrogen at position 3 of the thiadiazole ring, involved in an Sto-N delocalized thiadiazole-2-thiolate structure, which is thermodynamically more favorable in the presence of Na+ . Experimental assays refute a plausible concerted 1,3-sigmatropic S- to Nrearrangement of MTSB that would lead to BMTT. Hence, contradicting the nucleophilicity indices of sulfur (from thiol) and nitrogen atoms of 5-methyl-1,3,4-thiadiazole-2-thiol, it is believed that an exotic nucleophilic attack by the nitrogen at 3-position of this reagent to the sp2 carbon in position 3 of pseudo-saccharyl chloride should take place. Besides, the crystal structures of the MTSB and BMTT hybrids were investigated in detail by X-ray crystallography.