Stefano Banfi

Synthetic enzymes—4 : Highly enantioselective epoxidation by means of polyaminoacids in a triphase system: influence of structural variations within the catalysts

Abstract The asymmetric epoxidation of chalcone and other electron-poor olefins in a triphase system (water-organic solvent-polyaminoacid) affords optically active oxiranes. The influence of the molecular structure of catalysts and of their secondary conformation on the enantioselectivity of the reaction has also been examined.

Asymmetric epoxidation of electron-poor olefins. V: Influence on stereoselectivity of the structure of poly-α-aminoacids used as catalysts

Abstract New poly-α-aminoacids modified at the C orN-terminal groups are synthetised and employed in the asymmetric epoxidation of chalcone. Their influence on the stereoselectivity of the reaction is studied.

Synthesis and antibacterial activity of novel cationic BODIPY photosensitizers

BODIPYs are versatile dyes never tested before in photodynamic application against prokaryotes. We specifically synthesized two cationic BODIPYs (compounds 3 and 4) with structural features suitable for this pourpose. The novel BODIPYs are both characterized by the presence of one pyridinium cationic group on position 8 and two iodine atoms on 2,6-positions of the dipyrrolylmethene structure, thus ensuring solubility in 1/1 water/organic solvent mixture and a good singlet oxygen formation rate. These two photosensitizers differ only in the moiety linked on pyridine nitrogen atom as 3 and 4 bear a methyl and a benzyl group, respectively. BODIPYs 3 and 4 were tested against two bacterial model strains, the Gram positive Staphylococcus xylosus and the Gram negative Escherichia coli. Despite the small structural modification between 3 and 4, a remarkable difference in photocatalyzed efficacy against the model microorganisms was observed. In particular methylated compound 3 was found much more efficient with respect to the benzylated one (4). As consequence, in-depth examination of the antibacterial activity was performed using the more efficient compound 3. A high degree of phototoxicity (>6 log units) was observed with the photosensitizer 0.5 μM against S. xylosus and 5.0 μM against E. coli, following 5 min irradiation with a green LED device (light dose 1.38 J/cm(2)). No dark toxicity was observed up to 40 μM. Further studies indicate that the phototoxic efficacy induced by BODIPY 3 depends both on its concentration and on light dose, which can be specifically modulated to achieve the eradication of the tester strains.

Porphyrins and azaporphines as catalysts in alkene epoxidations with peracetic acid

the reactivities of five MnIII(Cl) - porphinoids were compared in the catalytic alkene epoxidations in CH3CN solution with peracetic acid as primary oxidant. Porphyrins 1 and 2 bearing Cl and NO2 substituents showed the best efficiency while tetraazaporphyrin 5 was found to be an interesting catalyst for terminal alkene epoxidations.

Towards epoxidation catalysts for fluorous biphase systems: Synthesis and properties of two Mn(III)-tetraarylporphyrins bearing perfluoroalkylamido tails

Abstract Two new Mn(III)-tetraarylporphyrins Mn-1 and Mn-2 bearing one amido-bonded n-C7F15 chain on each meso-aryl group have been synthesized. The presence of four perfluoroalkyl tails strongly influences the solubility of these compounds in common organic solvents, but it is not sufficient to impart solubility in fluorocarbons. The catalytic activity of the new complexes was tested in alkene epoxidations employing aqueous NaOCl as oxygen donor. Results show that Mn-2 is more active than Mn(III)-5,10,15,20-tetrakis-(2,6-dichlorophenyl)porphyrin, one of the most efficient porphyrinic catalysts for hydrocarbon oxygenation.

Synthesis of chiral Mn(III)-meso-tetrakis-[2.2]-p-cyclophanyl-porphyrin: a new catalyst for enantioselective epoxidation

Abstract The synthesis of Mn(III)-complexes of new chiral porphyrins 1a and 1b prepared by condensation of enantiomerically pure [2.2]- p -cyclophane-4-carbaldehyde and pyrrole are described. These compounds were used as catalysts in epoxidation reactions of prochiral alkenes, carried out in the presence of aqueous NaOCl at pH = 10.0 as oxygen donor and small amounts of 4-tert-butylpyridine as axial ligand, in CH 2 Cl 2 H 2 O two-phase conditions at 0°C. Results indicate a satisfactory catalytic efficiency (up to 700 overall turnovers), with enantiomeric excesses in the range 22–31%.

Synthesis and photodynamic activity of a panel of BODIPY dyes

Eight BODIPY dyes were synthesized and used as photosensitizers (PSs) on the human colon carcinoma cell line HCT116. In this panel of molecules, the structure varies in the substituents on pyrrole 2, 6 positions and on the phenyl ring at the indacene 8 position. For these compounds relevant physico-chemical parameters, such as singlet oxygen production, fluorescent quantum yield, absorbance profile and a relative rank of lipophilicity were determined. Our results indicate that some of these novel PSs are very effective in reducing the growth/viability of HCT116 cells when irradiated with a green LED source, whereas they are practically devoid of activity in the dark, up to 5 μM. To evaluate whether cell death is induced under these conditions, flow cytometric analysis of the percentage of apoptotic and autophagic cells was performed on four molecules, chosen for their efficacy/structural characteristics. Our data indicate that phototoxicity likely occurs mainly through apoptotic cell death, whereas autophagy seems to play a minor role in determining cell fate. Furthermore, the relationship between singlet oxygen generation and the PS efficacy is confirmed, thus underscoring the importance of the heavy-atom effect and of the presence of an aryl substituent at dipyrromethene 8 (meso) position. Among the PSs here described, the most efficient BODIPY was successfully tested on three other human cancer cell lines of different tissue origin, MCF7 (breast), A2780 and A2780/CP8 (ovary, sensitive and resistant to cisplatin, respectively), yielding IC(50) values comparable to those obtained on HCT116.

Oxidative cleavage of plasmid bluescript by water-soluble Mn-porphyrins and artificial oxidants or molecular oxygen

A set of eight Mn(III)-porphyrins were used as catalysts in oxidative demolition of Plasmid Bluescript, to the nicked and linear forms, in the presence of different oxygen donors (NaOCl, H(2)O(2), AcOOH, t-BuOOH). The efficiency of the catalytic system is related to a combination of factors such as porphyrin structures, pH of the aqueous phase and nature of the primary oxidant. The highest catalytic activity was observed when ionic porphyrins were used as catalyst (the cationic being more active than the anionic) and NaOCl was used as primary oxidant at pH 9.5; in contrast, lipophilic catalysts proved to be completely unreactive towards the DNA, whichever oxidant used. The plasmid demolition was also achieved by irradiating the reaction mixture, containing Zinc porphyrins, with a white lamp; under these conditions, the highest efficiency was again observed with meso-tetra(1-methyl-4-pyridyl)porphyrin. However, preliminary experiments of photo activation applied on tumour cells (HCT 116) showed no dead cells with cationic porphyrin, while the amphiphilic Zn-tetra(4-hydroxyphenyl)porphyrin gave IC(50) values at 5 x 10(-2) microM concentration (37.1 ng/mL).

Asymmetric Catalytic Epoxydation by Means of Cyclodextrins

Abstract Asymmetric synthesis occurs in the epoxidation of trans-chalcone with sodium hypochlorite and cyclodextrins, with enantiomeric excess up to 11%.

Using long bis(4-pyridyl) ligands designed for the self-assembly of coordination frameworks and architectures

Five long bis(4-pyridyl) ligands with different tether groups, namely 1,4-phenylenebis(4-pyridylmethanone) (L1), bis(4-pyridyl)terephthalate (L2), 1,5-bis(pyridin-4-ylmethoxy)naphthalene (L3), 1,4-bis[2-(4-pyridyl)ethenyl]benzene (L4) and 4,4′-bis(pyridin-4-ylmethoxy)biphenyl (L5), have been synthesized and employed for the self-assembly of coordination polymers and architectures, with the aim of obtaining structural motifs characterized by long metal–metal separations. Six coordination products (compounds 1–6) have been obtained by reacting the ligands with cobalt(II) nitrate in all cases but one, in which zinc(II) triflate was used. The crystal structures show a variety of structural motifs. [Co(L2)(NO3)2(MeCN)]·MeCN (2) and [Co(L5)(NO3)2] (5) contain one-dimensional polymeric chains (linear, with a period of 19.64 A in 2; zigzag, with a period of 38.65 A in 5). [Zn(L1)(H2O)4](CF3SO3)2·(L1)2·H2O (1) and [Co(L4)2(H2O)4](NO3)2·(L4)4·(H2O)8 (4) exhibit extended three-dimensional and two-dimensional arrays, respectively, sustained both by coordinative and hydrogen bonds. Compound 3, [Co(L3)2(NO3)2]·(CH2Cl2)2, consists of two-dimensional layers of large rhombic meshes (diagonals of the rhombus 15.43 and 35.74 A), while compound 6, [Co2(L5)4(NO3)4]·(Me2CO)2, contains discrete dinuclear molecules, consisting of large rings with appendages, which exhibit an exceptionally long dimension of 62.84 A and form columnar supramolecular arrays.