A new platform for the synthesis of diketopyrrolopyrrole derivatives via nucleophilic aromatic substitution reactions

Diketopyrrolopyrroles (DPPs) are a versatile group of dyes and pigments with valuable optoelectronic properties. In this work we report the synthesis of highly fluorescent DPP derivatives through straightforward nucleophilic aromatic substitution reactions with thiols and phenols. These nucleophilic substitutions occur at room temperature and manifest a remarkable selectivity for the 4-position of the pentafluorophenyl groups. Both symmetrical (disubstitution) and non-symmetrical (monosubstitution) DPP derivatives are formed in excellent overall yields. The optical properties of the newly synthesized compounds are also discussed. The new platform may be useful for bioorthogonal chemistry.

An ambipolar PEDOT-perfluorinated porphyrin electropolymer: application as an active material in energy storage systems

The development of functional organic materials is crucial for the advancement of various fields, such as optoelectronics, energy storage, sensing, and biomedicine. In this context, we successfully prepared a stable ambipolar perfluoroporphyrin-based polymeric film by electrochemical synthesis. Our strategy involved the synthesis of a novel tetra-pentafluorophenyl porphyrin covalently linked to four 3,4-ethylenedioxythiophene (EDOT) moieties. The resulting monomer, EDOT-TPPF16, was obtained through a straightforward synthetic approach with a good overall yield. The unique molecular structure of EDOT-TPPF16 serves a dual function, with EDOT moieties allowing electropolymerization for polymeric film formation, while the electron-acceptor porphyrin core enables electrochemical reduction and electron transport. The electrochemical polymerization permits the polymer (PEDOT-TPPF16) synthesis and film formation in a reproducible and controllable manner in one step at room temperature. Spectroelectrochemical experiments confirmed that the porphyrin retained its optoelectronic properties within the polymeric matrix after the electrochemical polymerization. The obtained polymeric material exhibited stable redox capabilities. Current charge-discharge cycles and electrochemical impedance spectroscopy of the electrochemically generated organic film demonstrated that the polymer could be applied as a promising active material in the development of supercapacitor energy storage devices.

Synthesis of new representatives of A3B-type carboranylporphyrins based on meso-tetra(pentafluorophenyl)porphyrin transformations

A carboranylporphyrin of A3B-type bearing a single pentafluorophenyl ring was prepared through the regioselective nucleophilic aromatic substitution reaction of the p-fluorine atoms in 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin with 9-mercapto-m-carborane. The reaction of this porphyrin with sodium azide led to the selective substitution of the p-fluorine atom in the pentafluorophenyl substituent with an azide functionality which upon reduction with SnCl2 resulted in the formation of the corresponding porphyrin with an amino group. Pentafluorophenyl-substituted A3B-porphyrins were studied and transformed to thiol and amino-substituted compounds allowing for the preparation of porphyrins with different reactive groups such as hydroxy and amino derivatives capable for further functionalization and conjugation of these porphyrins to other substrates. In addition, conjugates containing maleimide or biotin entities in the structure of carborane A3B-porphyrin were also synthesized based on the amino-substituted A3B-porphyrin. The structures of the prepared carboranylporphyrins were determined by UV-vis, IR, 1H, 19F, 11B NMR spectroscopic data and MALDI mass spectrometry.

5,10,15,20-Tetrakis(pentafluorophenyl)porphyrin as a Functional Platform for Peptide Stapling and Multicyclisation

Polyfluorinated aromatic reagents readily react with thiolates via nucleophilic aromatic substitution (SN Ar) and provide excellent scaffolds for peptide cyclisation. Here we report a robust and versatile platform for peptide stapling and multicyclisation templated by 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin, opening the door to the next generation of functional scaffolds for 3D peptide architectures. We demonstrate that stapling and multicyclisation occurs with a range of non-protected peptides under peptide-compatible conditions, exhibiting chemoselectivity and wide-applicability. Peptides containing two cysteine residues are readily stapled, and the remaining perfluoroaryl groups permit the introduction of a second peptide in a modular fashion to access bicyclic peptides. Similarly, peptides with more than two cysteine residues can afford multicyclic products containing up to three peptide 'loops'. Finally, we demonstrate that a porphyrin-templated stapled peptide containing the Skin Penetrating and Cell Entering (SPACE) peptide affords a skin cell penetrating conjugate with intrinsic fluorescence.

Microwave-Assisted Synthesis and Spectral Properties of Pyrrolidine-Fused Chlorin Derivatives

In this work we pursued research involving the microwave-assisted N-alkylation of a NH pyrrolidine-fused chlorin with methyl 4-(bromomethyl) benzoate and subsequent ester hydrolysis as a straightforward strategy to obtain carboxylic acid functionality in the pyrrolidine-fused chlorin, as a single reaction product. We studied the reaction's scope by extending the N-alkylation of the free-base chlorin and its corresponding Zn(II) complex to other alkyl halides, including 1,4-diiodobutane, N-(2-bromoethyl)phthalimide, and 2-bromoethanaminium bromide. In addition, two new chlorin-dansyl dyads were synthesized by reacting dansyl chloride with the 2-aminoethyl pyrrolidine-fused chlorin (dyad 6) and NH pyrrolidine-fused chlorin (dyad 7). According to spectral studies, the linker length between the two fluorophores influences the response of the dyads to the solvent polarity. Because of the simplicity of these approaches, we believe it will enable access to a vast library of custom-tailored N-functionalized chlorins while preserving their important absorption and emission spectra as photosensitizers in photodynamic therapy (PDT) of cancer and photodynamic inactivation (PDI) of microorganisms.

Tuning the Molecular Structure of Corroles to Enhance the Antibacterial Photosensitizing Activity

The increase in the antibiotic resistance of bacteria is a serious threat to public health. Photodynamic inactivation (PDI) of micro-organisms is a reliable antimicrobial therapy to treat a broad spectrum of complex infections. The development of new photosensitizers with suitable properties is a key factor to consider in the optimization of this therapy. In this sense, four corroles were designed to study how the number of cationic centers can influence the efficacy of antibacterial photodynamic treatments. First, 5,10,15-Tris(pentafluorophenyl)corrole (Co) and 5,15-bis(pentafluorophenyl)-10-(4-(trifluoromethyl)phenyl)corrole (Co-CF₃) were synthesized, and then derivatized by nucleophilic aromatic substitution with 2-dimethylaminoethanol and 2-(dimethylamino)ethylamine, obtaining corroles Co-3NMe₂ and Co-CF₃-2NMe₂, respectively. The straightforward synthetic strategy gave rise to macrocycles with different numbers of tertiary amines that can acquire positive charges in an aqueous medium by protonation at physiological pH. Spectroscopic and photodynamic studies demonstrated that their properties as chromophores and photosensitizers were unaffected, regardless of the substituent groups on the periphery. All tetrapyrrolic macrocycles were able to produce reactive oxygen species (ROS) by both photodynamic mechanisms. Uptake experiments, the level of ROS produced in vitro, and PDI treatments mediated by these compounds were assessed against clinical strains: methicillin-resistant Staphylococcus aureus and Klebsiella pneumoniae. In vitro experiments indicated that the peripheral substitution significantly affected the uptake of the photosensitizers by microbes and, consequently, the photoinactivation performance. Co-3NMe₂ was the most effective in killing both Gram-positive and Gram-negative bacteria (inactivation > 99.99%). This work lays the foundations for the development of new corrole derivatives having pH-activable cationic groups and with plausible applications as effective broad-spectrum antimicrobial photosensitizers.

Porphyrin Polymers Bearing N,N'-Ethylene Crosslinkers as Photosensitizers against Bacteria

The appearance of microbes resistant to antibiotics requires the development of alternative therapies for the treatment of infectious diseases. In this work two polymers, PTPPF₁₆-EDA and PZnTPPF₁₆-EDA, were synthesized by the nucleophilic aromatic substitution of 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin and its Zn(II) complex with ethylenediamine, respectively. In these structures, the tetrapyrrolic macrocycles were N,N'-ethylene crosslinked, which gives them greater mobility. The absorption spectra of the polymers showed a bathochromic shift of the Soret band of ~10 nm with respect to the monomers. This effect was also found in the red fluorescence emission peaks. Furthermore, both polymeric materials produced singlet molecular oxygen with high quantum yields. In addition, they were capable of generating superoxide anion radicals. Photodynamic inactivation sensitized by these polymers was tested in Staphylococcus aureus and Escherichia coli bacteria. A decrease in cell viability greater than 7 log (99.9999%) was observed in S. aureus incubated with 0.5 μM photosensitizer upon 30 min of irradiation. Under these conditions, a low inactivation of E. coli (0.5 log) was found. However, when the cells were treated with KI, the elimination of the Gram-negative bacteria was achieved. Therefore, these polymeric structures are interesting antimicrobial photosensitizing materials for the inactivation of pathogens.

Computational Evaluation of Potential Molecular Catalysts for Nitrous Oxide Decomposition

Nitrous oxide (N₂O) is a potent greenhouse gas (GHG) with limited use as a mild anesthetic and underdeveloped reactivity. Nitrous oxide splitting (decomposition) is critical to its mitigation as a GHG. Although heterogeneous catalysts for N₂O decomposition have been developed, highly efficient, long-lived solid catalysts are still needed, and the details of the catalytic pathways are not well understood. Reported herein is a computational evaluation of three potential molecular (homogeneous) catalysts for N₂O splitting, which could aid in the development of more active and robust catalysts and provide deeper mechanistic insights: one Cu(I)-based, [(CF₃O)₄Al]Cu (A-1), and two Ru(III)-based, Cl(POR)Ru (B-1) and (NTA)Ru (C-1) (POR = porphyrin, NTA = nitrilotriacetate). The structures and energetic viability of potential intermediates and key transition states are evaluated according to a two-stage reaction pathway: (A) deoxygenation (DO), during which a metal-N₂O complex undergoes N-O bond cleavage to produce N₂ and a metal-oxo species and (B) (di)oxygen evolution (OER), in which the metal-oxo species dimerizes to a dimetal-peroxo complex, followed by conversion to a metal-dioxygen species from which dioxygen dissociates. For the (F-L)Cu(I) activator (A-1), deoxygenation of N₂O is facilitated by an O-bound (F-L)Cu-O-N₂ or better by a bimetallic N,O-bonded, (F-L)Cu-NNO-Cu(F-L) complex; the resulting copper-oxyl (F-L)Cu-O is converted exergonically to (F-L)Cu-(η²,η²-O₂)-Cu(F-L), which leads to dioxygen species (F-L)Cu(η²-O₂), that favorably dissociates O₂. Key features of the DO/OER process for (POR)ClRu (B-1) include endergonic N₂O coordination, facile N₂ evolution from LR'u-N₂O-RuL to Cl(POR)RuO, moderate barrier coupling of Cl(POR)RuO to peroxo Cl(POR)Ru(O₂)Ru(POR)Cl, and eventual O₂ dissociation from Cl(POR)Ru(η¹-O₂), which is nearly thermoneutral. N₂O decomposition promoted by (NTA)Ru(III) (C-1) can proceed with exergonic N₂O coordination, facile N₂ dissociation from (NTA)Ru-ON₂ or (NTA)Ru-N₂O-Ru(NTA) to form (NTA)Ru-O; dimerization of the (NTA)Ru-oxo species is facile to produce (NTA)Ru-O-O-Ru(NTA), and subsequent OE from the peroxo species is moderately endergonic. Considering the overall energetics, (F-L)Cu and Cl(POR)Ru derivatives are deemed the best candidates for promoting facile N₂O decomposition.

Charge density distribution effect in pyrrolidine-fused chlorins on microbial uptake and antimicrobial photoinactivation of microbial pathogens

Two novels structurally related pyrrolidine-fused chlorins were synthesized from 5,10,15,20-tetrakis(pentafluorophenyl)chlorin by nucleophilic aromatic substitution of the para-fluoro groups. The reaction with 2-dimethylaminoethanol produced TPCF₁₆-NMe₂ in 77% yield, while TPCF₁₆-NBu was obtained using butylamine in 87% yield. The latter was extensively methylated to form TPCF₁₆-N⁺Bu in 92% yield. The synthetic strategy was designed to compare the effect of charge density distribution on chlorin in the efficacy to induce photodynamic inactivation of pathogens. TPCF₁₆-NMe₂ has five tertiary amines that can acquire positive charges in aqueous medium by protonation. Furthermore, four of the cationic groups are located in amino groups linked to the chlorine macrocycle by an aliphatic structure of two carbon atoms, which gives it greater movement capacity. In contrast, TPCF₁₆-N⁺Bu presents intrinsic positive charges on aromatic rings. Absorption and fluorescence emission properties were not affected by the peripheral substitution on the chlorin macrocycle. Both photosensitizers (PSs) were able to form singlet molecular oxygen and superoxide anion radical in solution. Uptake and photodynamic inactivation mediated by these chlorins were examined on Staphylococcus aureus and Escherichia coli. Both phototherapeutic agents produced efficient photoinactivation of S. aureus. However, only TPCF₁₆-NMe₂ was rapidly bound to E. coli cells and this chlorin was effective to photoinactivate both strains of bacteria using lower concentrations and shorter irradiation periods. Our outcomes reveal that the charge density distribution is a key factor to consider in the development of new PSs. Accordingly, this work stands out as a promising starting point for the design of new tetrapyrrolic macrocycles with application in PDI.

Novel fluorinated ring-fused chlorins as promising PDT agents against melanoma and esophagus cancer

Investigation of novel 4,5,6,7-tetrahydropyrazolo[1,5-a]pyridine-fused chlorins, derived from 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin, as PDT agents against melanoma and esophagus cancer is disclosed. Diol and diester fluorinated ring-fused chlorins, including derivatives with 2-(2-hydroxyethoxy)ethanamino groups at the phenyl rings, were obtained via a two-step methodology, combining SNAr and [8π + 2π] cycloaddition reactions. The short-chain PEG groups at the para-position of the phenyl rings together with the diol moiety at the fused pyrazole ring promote a red-shift of the Soret band, a decrease of the fluorescence quantum yield and an increase of the singlet oxygen formation quantum yield, improving the photophysical characteristics required to act as a photosensitizer. Introduction of these hydrophilic groups also improves the incorporation of the sensitizers by the cells reaching cellular uptake values of nearly 50% of the initial dose. The rational design led to a photosensitizer with impressive IC50 values, 13 and 27 nM against human melanoma and esophageal carcinoma cell lines, respectively.

Post Synthetic Modification of Planar Antiaromatic Hexaphyrin (1.0.1.0.1.0) by Regio-Selective, Sequential SNAr

In spite of unique structural, spectroscopic and redox properties, the synthetic variants of the planar, antiaromatic hexaphyrin (1.0.1.0.1.0) derivatives 2, has been limited due to the low yields and difficulty in access to the starting material. A chemical modification of the meso-substituents could be good alternative overcoming the synthetic barrier. Herein, we report a regio-selective nucleophilic aromatic substitution (S_NAr) of meso-pentafluorophenyl group in rosarrin 2 with catechol. The reaction afforded benzodioxane fused rosarrin 3 as single product with high yield. The intrinsic antiaromatic character of the starting rosarrin 2 retained throughout the reactions. Clean, two electron reduction was achieved by treatment of 3 with SnCl₂•2H₂O affording 26π-electron aromatic rosarrin 4. The synthesized compounds exhibited noticeable changes in photophysical and redox properties compared with starting rosarrin 2.

First-row transition metal porphyrins for electrocatalytic hydrogen evolution — a SPP/JPP Young Investigator Award paper

A series of first-row transition metal complexes of tetrakis(pentafluorophenyl)porphyrin (1), denoted as 1-M (M [Formula: see text] Mn, Fe, Co, Ni, Cu, and Zn), were synthesized and examined as electrocatalysts for the hydrogen evolution reaction (HER). All these transition metal porphyrins were shown to be active for HER in acetonitrile using trifluoroacetic acid (TFA) as the proton source. The molecular nature and the stability of these metal porphyrins when functioning as HER catalysts were confirmed, and all catalysts gave Faradaic efficiency of >97% for H2 generation during bulk electrolysis. Importantly, by using 1-Cu, a remarkably high turnover frequency (TOF) of 48500 s[Formula: see text] 1-Cu the most efficient among this series of metal porphyrin catalysts. This TOF value also represents one of the highest values reported in the literature. In addition, electrochemical analysis demonstrated that catalytic HER mechanisms with these 1-M complexes are different. These results show that with the same porphyrin ligand, the change of metal ions will have significant impact on both catalytic efficiency and mechanism. This work for the first time provides direct comparison of electrocatalytic HER features of transition metal complexes of tetrakis(pentafluorophenyl)porphyrin under identical conditions, and will be valuable for future design and development of more efficient HER electrocatalysts of this series.

Crystal structure of 2,3-dimeth-oxy-meso-tetra-kis(penta-fluoro-phen-yl)morpholino-chlorin methyl-ene chloride 0.44-solvate

The title morpholino-chlorin, C46H16F20N4O3, was crystallized from hexa-ne/methyl-ene chloride as its 0.44 methyl-ene chloride solvate, C46H16F20N4O3·0.44CH2Cl2. The morpholino-chlorin was synthesized by stepwise oxygen insertion into a porphyrin using a 'breaking and mending strategy': NaIO4-induced diol cleavage of the corresponding 2,3-di-hydroxy-chlorin with in situ methanol-induced, acid-catalyzed intra-molecular ring closure of the inter-mediate secochlorins bis-aldehyde. Formally, one of the pyrrolic building blocks was thus replaced by a 2,3-di-meth-oxy-morpholine moiety. Like other morpholino-chlorins, the macrocycle of the title compound adopts a ruffled conformation, and the modulation of the porphyrinic π-system chromophore induces a red-shift of its optical spectrum compared to its corresponding chlorin analog. Packing in the crystal is governed by inter-actions involving the fluorine atoms of the penta-fluoro-phenyl substituents, dominated by C-H⋯F inter-actions, and augmented by short fluorine⋯fluorine contacts, C-F⋯π inter-actions, and one severely slipped π-stacking inter-action between two penta-fluoro-phenyl rings. The solvate methyl-ene chloride mol-ecule is disordered over two independent positions around an inversion center with occupancies of two × 0.241 (5) and two × 0.199 (4), for a total site occupancy of 88%.

Site-Selective Modification of a Porpholactone-Selective Synthesis of 12,13- and 17,18-Dihydroporpholactones

The reaction of meso-tetrakis(pentafluorophenyl)porpholactone with azomethine ylides and nitrones affords pyrrolidine-fused and isoxazolidine-fused dihydroporpholactones that display, respectively, isobacteriochlorin- and chlorin-type UV–Vis spectra. These reactions are site-selective, yielding, respectively, 17,18- or 12,13-dihydroporpholactones. The crystal and molecular features of pyrrolidine-fused and isoxazolidine-fused dihydroporpholactones were unveiled from single-crystal X-ray diffraction studies.

Fluorinated maleimide-substituted porphyrins and chlorins: synthesis and characterization

Maleimide-containing fluorinated porphyrins and chlorins were prepared based on the reaction of Zn(II) or Ni(II) complexes of 5,10,15,20-tetrakis(4-amino-2,3,5,6-tetrafluorophenyl)porphyrin and chlorin with maleic anhydride. Porphyrin maleimide derivatives were also prepared by the reaction of 5,10,15,20-tetrakis(4-azido-2,3,5,6-tetrafluorophenyl)porphyrinato Zn(II) or Ni(II) with N-propargylmaleimide via the CuAAC click reaction to afford fluorinated porphyrin-triazole-maleimide conjugates. New maleimide derivatives were isolated in reasonable yields and identified by UV-vis, 1H NMR, 19F NMR spectroscopy and mass-spectrometry.

A Convenient Synthesis of Pentaporphyrins and Supramolecular Complexes with a Fulleropyrrolidine

A simple and straightforward synthesis of diporphyrins and pentaporphyrins is reported here. The supramolecular interactions of the new porphyrin derivatives with C60 and PyC60 (a pyridyl [60]fulleropyrrolidine) were evaluated by absorption and fluorescence titrations in toluene. While no measurable modifications of the absorption and fluorescence spectra were observed upon addition of C60 to the porphyrin derivatives, the addition of PyC60 to the corresponding mono-Zn(II) porphyrins resulted in the formation of Zn(porphyrin)-PyC60 coordination complexes and the binding constants were calculated. Results show that the four free-base porphyrin units in pentaporphyrin 6 have a significant contribution in the stabilization of the 6-PyC60 complex. The crystal and molecular features of the pentaporphyrin Zn5 were unveiled using single-crystal X-ray diffraction studies.

New Materials Based on Cationic Porphyrins Conjugated to Chitosan or Titanium Dioxide: Synthesis, Characterization and Antimicrobial Efficacy

The post-functionalization of 5,10,15-tris(1-methylpyridinium-4-yl)-20-(pentafluorophenyl)porphyrin tri-iodide, known as a highly efficient photosensitizer (PS) for antimicrobial photodynamic therapy (aPDT), in the presence of 3- or 4-mercaptobenzoic acid, afforded two new tricationic porphyrins with adequate carboxylic pending groups to be immobilized on chitosan or titanium oxide. The structural characterization of the newly obtained materials confirmed the success of the porphyrin immobilization on the solid supports. The photophysical properties and the antimicrobial photodynamic efficacy of the non-immobilized porphyrins and of the new conjugates were evaluated. The results showed that the position of the carboxyl group in the mercapto units or the absence of these substituents in the porphyrin core could modulate the action of the photosensitizer towards the bioluminescent Gram-negative Escherichia coli bacterium. The antimicrobial activity was also influenced by the interaction between the photosensitizer and the type of support (chitosan or titanium dioxide). The new cationic porphyrins and some of the materials were shown to be very stable in PBS and effective in the photoinactivation of E. coli bacterium. The physicochemical properties of TiO2 allowed the interaction of the PS with its surface, increasing the absorption profile of TiO2, which enables the use of visible light, inactivating the bacteria more efficiently than the corresponding PS immobilized on chitosan.

Photodegradation of metoprolol using a porphyrin as photosensitizer under homogeneous and heterogeneous conditions

Porphyrins are known as effective photosensitizers and can be an interesting key in phototreatment of water contaminated with micropollutants such as pharmaceuticals. They already showed to be efficient photocatalysts for the degradation of dyes, chlorophenols and other pollutants. This work demonstrates the applicability of 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (H₂TF₅PP) as photosensitizer for treatment of water contaminated with metoprolol, a highly prescribed β-blocker, which is not completely removed in sewage treatment plants. Studies were firstly developed under homogeneous conditions with simulated solar radiation and porphyrin was found to be efficient in the photodegradation of metoprolol, following a pseudo-first order kinetics with ca. 90% metoprolol degradation after 12 h. Experiments in presence of scavengers confirmed the mechanism of degradation via singlet oxygen. Appearance of several new peaks in HPLC chromatograms indicates the formation of products, identified by HPLC-MSⁿ. Furthermore, the porphyrin was immobilized on a silica support and used as heterogeneous photocatalyst in degradation of metoprolol. Experiments using this heterogeneous photocatalyst under real solar irradiation were also performed, and similar results were obtained. Kinetic comparison of metoprolol photodegradation in buffer solution and in real wastewater treatment plant effluent showed that the efficiency of the immobilized porphyrin was not decreased by the complex matrix of the effluent.

Supramolecular Hybrid Material Based on Engineering Porphyrin Hosts for an Efficient Elimination of Lead(II) from Aquatic Medium

Porphyrins show great promise for future purification demands. This is largely due to their unique features as host binding molecules that can be modified at the synthetic level, and largely improved by their incorporation into inorganic based materials. In this study, we assessed the efficacy of a hybrid material obtained from the immobilization of 5,10,15,20-tetrakis(pentafluorophenyl)-porphyrin on silica surface to remove Pb(II), Cu(II), Cd(II), and Zn(II) ions from water. The new organic-inorganic hybrid adsorbent was fully characterized by adequate techniques and the results show that the hybrid exhibits good chemical and thermal stability. From batch assays, it was evaluated how the efficacy of the hybrid was affected by the pH, contact time, initial metal concentration, and temperature. The adsorption kinetic and isotherms showed to fit the recent developed fractal-like pseudo-second-order model and Langmuir–Freundlich model respectively. The highest adsorption capacities for Pb(II), Cu(II), Cd(II), and Zn(II) ions were 187.36, 125.17, 82.45, and 56.23 mg g⁻¹, respectively, at pH 6.0 and 25 °C. This study also shows that metal cations from real river water samples can be efficient removed in the presence of the new adsorbent material.

A New Protocol for the Synthesis of New Thioaryl-Porphyrins Derived from 5,10,15,20-Tetrakis(pentafluorophenyl)porphyrin: Photophysical Evaluation and DNA-Binding Interactive Studies

A new protocol for the preparation of thioaryl-porphyrins is described. The compounds were prepared from different disulfides employing NaBH₄ as a reducing agent. The methodology allowed the preparation of four different thioaryl-porphyrins in very-good to excellent yields under soft conditions, such as short reaction times and smooth heating. Additionally, the photophysical properties of new compounds were determined and experimental and theoretical DNA interactions were assessed.

Revisiting Current Photoactive Materials for Antimicrobial Photodynamic Therapy

Microbial infection is a severe concern, requiring the use of significant amounts of antimicrobials/biocides, not only in the hospital setting, but also in other environments. The increasing use of antimicrobial drugs and the rapid adaptability of microorganisms to these agents, have contributed to a sharp increase of antimicrobial resistance. It is obvious that the development of new strategies to combat planktonic and biofilm-embedded microorganisms is required. Photodynamic inactivation (PDI) is being recognized as an effective method to inactivate a broad spectrum of microorganisms, including those resistant to conventional antimicrobials. In the last few years, the development and biological assessment of new photosensitizers for PDI were accompanied by their immobilization in different supports having in mind the extension of the photodynamic principle to new applications, such as the disinfection of blood, water, and surfaces. In this review, we intended to cover a significant amount of recent work considering a diversity of photosensitizers and supports to achieve an effective photoinactivation. Special attention is devoted to the chemistry behind the preparation of the photomaterials by recurring to extensive examples, illustrating the design strategies. Additionally, we highlighted the biological challenges of each formulation expecting that the compiled information could motivate the development of other effective photoactive materials.

Photochemotherapeutic Properties of a Linear Tetrapyrrole Palladium(II) Complex displaying an Exceptionally High Phototoxicity Index

Photodynamic therapy (PDT) represents a minimally invasive and highly localized treatment strategy to ablate tumors with few side effects. In PDT, photosensitizers embedded within tumors are activated by light and undergo intersystem crossing, followed by energy transfer to molecular oxygen, resulting in the production of toxic singlet oxygen (¹O₂). Previously, we reported a robust, linear tetrapyrrole palladium(II) complex, Pd[DMBil1], characterized by its facile and modular synthesis, broad absorption profile, and efficient ¹O₂ quantum yield of Φ_Δ = 0.8 in organic media. However, the insolubility of this porphyrinoid derivative in aqueous solution prevents its use under biologically relevant conditions. In this work, we report the synthesis of Pd[DMBil1]-PEG₇₅₀, a water-soluble dimethylbiladiene derivative that is appended with a poly(ethylene) glycol (PEG) functionality. Characterization of this complex shows that this PEGylated biladiene architecture maintains the attractive photophysical properties of the parent complex under biologically relevant conditions. More specifically, the absorption profile of Pd[DMBil1]-PEG₇₅₀ closely matches that of Pd[DMBil1] and obeys the Beer-Lambert Law, suggesting that the complex does not aggregate under biologically relevant conditions. Additionally, the emission spectrum of Pd[DMBil1]-PEG₇₅₀ retains the fluorescence and phosphorescence features characteristic of Pd[DMBil1]. Importantly, the PEGylated photosensitizer generates ¹O₂ with Φ_Δ = 0.57, which is well within the range to warrant interrogation as a potential PDT agent for treatment of cancer cells. The Pd[DMBil1]-PEG₇₅₀ is biologically compatible, as it is taken up by MDA-MB-231 triple negative breast cancer (TNBC) cells and has an effective dose (ED₅₀) of only 0.354 μM when exposed to λ_ex > 500 nm light for 30 min. Impressively, the lethal dose (LD₅₀) of Pd[DMBil1]-PEG₇₅₀ without light exposure was measured to be 1.87 mM, leading to a remarkably high phototoxicity index of ∼5300, which is vastly superior to existing photosensitizers that form the basis for clinical PDT treatments. Finally, through flow cytometry experiments, we show that PDT with Pd[DMBil1]-PEG₇₅₀ induces primarily apoptotic cell death in MDA-MB-231 cells. Overall these results demonstrate that Pd[DMBil1]-PEG₇₅₀ is an easily prepared, biologically compatible, and well-tolerated photochemotherapeutic agent that can efficiently drive the photoinduced apoptotic death of TNBC cells.

Evaluation of meso-substituted cationic corroles as potential antibacterial agents

Cationic derivatives of 5,10,15-tris[4-(pyridin-4-ylsulphanyl)-2,3,5,6-tetrafluorophenyl]-corrolategallium(III)pyridine and 5,10,15-tris[4-(pyridin-2-ylsulfanyl)-2,3,5,6-tetrafluorophenyl]-correlategallium(III)pyridine were synthesized and their photosensitizing properties against the naturally bioluminescent Gram-negative bacterium Allivibrio fischeri were evaluated. The cationic corrole derivatives exhibited antibacterial activity at micromolar concentrations against this Gram-negative bacterium strain.

Novel Alkoxy-Substituted Dipyrrins and Near-IR BODIPY Dyes-Preparation and Photophysical Properties

Starting from 3-alkoxy-2-aryl-substituted pyrroles and aromatic aldehydes, a collection of new dipyrrins was prepared. Under the standard conditions of Treibs, these were converted into the corresponding boron dipyrrins (BODIPYs). Compounds of this type with alkoxy groups at C-3 position of both pyrrole subunits are new and hence the photophysical properties of this collection of novel dipyrrins and BODIPY dyes were investigated. The dipyrrins show absorption maxima up to 596 nm and emissions of up to 677 nm. For the BODIPY series a remarkable effect of the alkoxy groups was identified, resulting in red shifts for absorptions and emissions. The compound substituted with two 2-thien-2-yl groups and a meso-C₆ F₅ substituent shows an absorption maximum at 725 nm and emits at 754 nm and thus is a new representative of a near-IR BODIPY dye related to certain aza-BODIPYs. Our results demonstrate the influence of the alkoxy groups on the spectroscopic data and reveal the potential of 3-alkoxy-2-aryl-substituted pyrroles for the design of new fluorophores.

Synthesis, crystallographic characterization and homogeneous catalytic activity of novel unsymmetric porphyrins

Unsymmetric porphyrins containing both pentafluorophenyl (PFP = A) and 3,4-dimethoxyphenyl (DMP = B) substituents at the meso positions were prepared using Lindsey's methodology.

Synthesis under high hydrostatic pressure — a new method to prepare 5,10,15,20-tetrakis[4-(substituted amino)-2,3,5,6-tetrafluorophenyl]porphyrins

5,10,15,20-Tetrakis(pentafluorophenyl)porphyrin reacts with primary alkylamines and heterocyclic amines, at 50°C and under high pressure (450 MPa), to produce the [Formula: see text]-substituted tetraamino derivatives in high yields. Under similar conditions, the reaction with the bulky dibutylamine and dipentylamine affords the corresponding mono-substituted dialkylaminoporphyrins in 10% yield. This new protocol arises as a considerable improvement of the methods already known, which usually require high temperatures and are not effective when using secondary amines having long alkyl groups.

Strategies for Corrole Functionalization

This review covers the functionalization reactions of meso-arylcorroles, both at the inner core, as well as the peripheral positions of the macrocycle. Experimental details for the synthesis of all known metallocorrole types and for the N-alkylation reactions are presented. Key peripheral functionalization reactions such as halogenation, formylation, carboxylation, nitration, sulfonation, and others are discussed in detail, particularly the nucleophilic aromatic substitution and the participation of corroles in cycloaddition reactions as 2π or 4π components (covering Diels-Alder and 1,3-dipolar cycloadditions). Other functionalizations of corroles include a large diversity of reactions, namely Wittig reactions, reactions with methylene active compounds, formation of amines, amides, and imines, and metal catalyzed reactions. At the final section, the reactions involving oxidation and ring expansion of the corrole macrocycle are described comprehensively.

Nucleophilic Aromatic Substitution on Pentafluorophenyl-Substituted Dipyrranes and Tetrapyrroles as a Route to Multifunctionalized Chromophores for Potential Application in Photodynamic Therapy

The application of porphyrinoids in biomedical fields, such as photodynamic therapy (PDT), requires the introduction of functional groups to tune their solubility for the biological environment and to allow a coupling to other active moieties or carrier systems. A valuable motif in this regard is the pentafluorophenyl (PFP) substituent, which can easily undergo a regiospecific nucleophilic replacement (S_N Ar) of its para-fluorine atom by a number of nucleophiles. Here, it is shown that, instead of amino-substitution on the final porphyrinoid or BODIPY (boron dipyrromethene), the precursor 5-(PFP)-dipyrrane can be modified with amines (or alcohols). These dipyrranes were transformed into amino-substituted BODIPYs. Condensation of these dipyrranes with aldehydes gave access to trans-A₂ B₂ -porphyrins and trans-A₂ B-corroles. By using pentafluorobenzaldehyde, it was possible to introduce another para-fluorine atom, which enabled the synthesis of multifunctionalized tetrapyrroles. Furthermore, alkoxy- and amino-substituted dipyrranes were applied to the synthesis of A₃ B₃ -hexaphyrins. The polar porphyrins that were prepared by using this method exhibited in vitro PDT activity against several tumor cell lines.

The evolution of corrole synthesis — from simple one-pot strategies to sophisticated ABC-corroles

This review highlights synthesis procedures to obtain A3-, cis- and trans- A2B- and ABC-corroles. Synthesis methods from the early beginning of “corrole chemistry”, acid-catalyzed condensation methods of various building blocks (pyrrole, aldehyde, dipyrromethane, dipyrromethane-carbinol, and dipyrromethane-dicarbinol etc.), possible side reaction during Brønsted acid catalyzed reactions (scrambling), one-pot synthesis of corroles, and post-macrocyclization modification reactions of meso-substituted A3-corroles are discussed.

Porphyrin Macrocycle Modification: Pyrrole Ring-Contracted or -Expanded Porphyrinoids

In recent years, several synthetic strategies aiming at the peripheral functionalization of porphyrins were developed. Particularly interesting are those involving the modification of β-pyrrolic positions leading to pyrrole-modified porphyrins containing four-, five-, six- or seven-membered heterocycles. Azeteoporphyrins, porpholactones and morpholinoporphyrins are representative examples of such porphyrinoids. These porphyrin derivatives have recently gained an increasing interest due to their potential application in PDT, as multimodal imaging contrast agents, NIR-absorbing dyes, optical sensors for oxygen, cyanide, hypochlorite and pH, and in catalysis.