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Structurally diverse BODIPYs were evaluated for their phototoxic activity against four cancer cell lines in a PDT optimization approach. In particular, glycosylated dibromo-BODIPYs showed a high phototoxic effect, as well as pronounced cellular uptake.

Porphyrins are well studied molecules that are widely used in Photodynamic Therapy, aiming for the eradication of tumours, but also for the eradication of bacteria. The formulation of porphyrins is a crucial factor when developing photodynamic applications, due to the limited stability and low solubility of porphyrins in aqueous media. Our research group has previously demonstrated that porphyrins, and especially 5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin are easily encapsulated inside acetylated lignin spherical nanoparticles, while conserving their main photophysical features. In the present study we encapsulated 5,10,15,20-tetrakis(3-hydroxyphenyl)porphyrin, the precursor of the well-known photosensitizer Temoporfin, in acetylated lignin nanoparticles, yielding a stable formulation while keeping the photophysical properties of the encapsulated porphyrin. This formulation was tested as a photodynamic antibacterial agent against Staphylococcus aureus CIP 76.25 and Escherichia coli CIP 53.126, where it efficiently eradicated S. aureus, although also showing non-neglectable dark toxicity against the bacterial cells. In conclusion, the 3-hydroxyphenyl substituted porphyrin yielded nanoparticles physically and photophysically similar to those prepared with its isomer. However, the change in the position of the phenyl substituent seems to increase the dark toxicity of the nanoparticles, a phenomenon that still needs to be explored.

Poly(l-glutamic acid)-b-poly(Nγ-acetyl-l-2,4-diaminobutyric acid), P(Glu-b-NADA), amphiphilic block-co-polypeptides with different hydrophobic/hydrophilic ratios were synthesized as drug carriers for dermal delivery. The block-co-polypeptides were prepared using ring-opening polymerization (ROP) of γ-benzyl l-glutamate N-carboxyanhydride and polycondensation of the activated urethane derivative of Nγ-acetyl-l-2,4-diaminobutyric acid. Structures and conjugations of two blocks were successfully confirmed by 1H NMR, FTIR, DOSY NMR, GPC, and TGA. The nanocarriers were loaded with 5,10,15,20-tetrakis(3-hydroxyphenyl)porphyrin (m-THPP), a close congener of the approved photosensitizer 5,10,15,20-tetrakis(3-hydroxyphenyl)chlorin (m-THPC, temoporfin), and the loading capacity was found to be dependent on the composition of the block-co-polypeptides. Among the synthesized polymers, P(Glu55-b-NADA20) with moderate hydrophobic content showed the highest drug loading capacity of 4 wt % and self-aggregated into spherical nanoparticles with a size of 180–200 nm, which was confirmed by TEM and DLS. In an in vitro drug release study, P(Glu55-b-NADA20) could release m-THPP in a controllable manner. Furthermore, the synthesized polymer P(Glu55-b-NADA20) did not show high toxicity against HaCaT and HeLa cells up to 1000 and 500 μg mL–1, respectively, in an in vitro cell viability assay. Finally, it was shown in an ex vivo skin penetration study that the ionic amphiphilic block co-polypeptide enhanced the m-THPP penetration into human skin compared to base cream up to a factor of 12. m-THPP was released from P(Glu55-b-NADA20) to the viable epidermis while the polymer was deposited in the skin’s stratum corneum. Taking advantage of its excellent biodegradability, the low cytotoxcity, and efficient skin penetration, the synthesized block-co-polypeptide has the potential for future topical delivery systems.

This review follows the research, development and clinical applications of the photosensitizer 5,10,15,20-tetra(m-hydroxyphenyl)chlorin (mTHPC, temoporfin) in photodynamic (cancer) therapy (PDT) and other medical applications. Temoporfin is the active substance in the medicinal product Foscan® authorized in the EU for the palliative treatment of head and neck cancer. Chemistry, biochemistry and pharmacology, as well as clinical and other applications of temoporfin are addressed, including the extensive work that has been done on formulation development including liposomal formulations. The literature has been covered from 2009 to early 2022, thereby connecting it to the previous extensive review on this photosensitizer published in this journal [Senge, M. O. and J. C. Brandt (2011) Photochem. Photobiol. 87, 1240-1296] which followed its way from initial development to approval and clinical application.

Prodigiosenes are a family of red pigments with versatile biological activity. Their tripyrrolic core structure has been modified many times in order to manipulate the spectrum of activity. We have been looking systematically at prodigiosenes substituted at the C ring with alkyl chains of different lengths, in order to assess the relevance of this substituent in a context that has not been investigated before for these derivatives: Cu(II) complexation, DNA binding, self-activated DNA cleavage, photoinduced cytotoxicity and antimicrobial activity. Our results indicate that the hydrophobic substituent has a clear influence on the different aspects of their biological activity. The cytotoxicity study of the Cu(II) complexes of these prodigiosenes shows that they exhibit a strong cytotoxic effect towards the tested tumor cell lines. The Cu(II) complex of a prodigiosene lacking any alkyl chain excelled in its photoinduced anticancer activity, thus demonstrating the potential of prodigiosenes and their metal complexes for an application in photodynamic therapy (PDT). Two derivatives along with their Cu(II) complexes were also shown to be effective antibacterial agents towards S. aureus strains.

The development of new tumor models for anticancer drug screening is a challenge for preclinical research. Conventional cell-based in vitro models such as 2D monolayer cell cultures or 3D spheroids allow an initial assessment of the efficacy of drugs but they have a limited prediction to the in vivo effectiveness. In contrast, in vivo animal models capture the complexity of systemic distribution, accumulation, and degradation of drugs, but visualization of the individual steps is challenging and extracting quantitative data is usually very difficult. Furthermore, there are a variety of ethical concerns related to animal tests. In accordance with the 3Rs principles of Replacement, Reduction and Refinement, alternative test systems should therefore be developed and applied in preclinical research. The Hen's egg test on chorioallantoic membrane (HET-CAM) model provides the generation of vascularized tumor spheroids and therefore, is an ideal test platform which can be used as an intermediate step between in vitro analysis and preclinical evaluation in vivo. We developed a HET-CAM based intestine tumor model to investigate the accumulation and efficacy of nano-formulated photosensitizers. Irradiation is necessary to activate the phototoxic effect. Due to the good accessibility of the vascularized tumor on the CAM, we have developed a laser irradiation setup to simulate an in vivo endoscopic irradiation. The study presents quantitative as well as qualitative data on the accumulation and efficacy of the nano-formulated photosensitizers in a vascularized intestine tumor model.

The use of carbohydrate thiolates for facile, high-yielding, regio- and stereoselective nucleophilic substitution reactions of complex pentafluorophenyl-substituted porphyrinoids is reported. The title reaction has successfully been applied to calix[4]phyrin, calix[6]phyrin, and [28]hexaphyrin substrates. The novel glycoporphyrinoid products with their extraordinary structures and unique photophysical properties are soluble in aqueous solutions and can serve as platforms for applications in biomedicine, catalysis, coordination, or redox chemistry.

The generation of bio‐targetable photosensitizers is of utmost importance to the emerging field of photodynamic therapy and antimicrobial (photo‐)therapy. A synthetic strategy is presented in which chelating dipyrrin moieties are used to enhance the known photoactivity of iridium(III) metal complexes. Formed complexes can thus be functionalized in a facile manner with a range of targeting groups at their chemically active reaction sites. Dipyrrins with N‐ and O‐substituents afforded (dipy)iridium(III) complexes via complexation with the respective Cp*‐iridium(III) and ppy‐iridium(III) precursors (dipy=dipyrrinato, Cp*=pentamethyl‐η5‐cyclopentadienyl, ppy=2‐phenylpyridyl). Similarly, electron‐deficient [IrIII(dipy)(ppy)2] complexes could be used for post‐functionalization, forming alkenyl, alkynyl and glyco‐appended iridium(III) complexes. The phototoxic activity of these complexes has been assessed in cellular and bacterial assays with and without light; the [IrIII(Cl)(Cp*)(dipy)] complexes and the glyco‐substituted iridium(III) complexes showing particular promise as photomedicine candidates. Representative crystal structures of the complexes are also presented., Heteroleptic dipyrrinato iridium complexes were synthesized and evaluated for their phototoxic activity against tumor cells and bacteria, the Gram‐positive germ S. aureus and the Gram‐negative Germ P. aeruginosa. Specifically, glycosylated phenylpyridyl‐dipyrrinato complexes showed a high phototoxic effect against cells and S. aureus. Certain cyclopentadienyl‐dipyrrinato complexes exerted a high phototoxic effect on S. aureus and P. aeruginosa.

A synthetic strategy to BODIPY dyes is presented giving access to a range of new compounds relevant in the context of antimicrobial photodynamic therapy (aPDT). BODIPYs with the 8-(4-fluoro-3-nitrophenyl) and the 8-pentafluorophenyl substituents were used for the synthesis of new mono- and dibrominated BODIPYs. The para-fluorine atoms in these electron-withdrawing groups facilitate functional modification via nucleophilic aromatic substitution (SNAr) with a number of amines and thio-carbohydrates. Subsequently, the antibacterial phototoxic activity of these BODIPYs has been assessed in bacterial assays against the Gram-positive germ S. aureus and also against the Gram-negative germ P. aeruginosa. The bacterial assays allowed to identify substitution patterns which ensured antibacterial activity not only in phosphate-buffered saline (PBS) but also in the presence of serum, hereby more realistically modelling the complex biological environment that is present in clinical applications.

An adaptable approach toward cleavable nanoparticle carrier systems for photodynamic therapy (PDT) is presented, comprising a biocompatible carrier loaded with multiple photosensitizer (PS) molecules related to the clinically employed PS Temoporfin, two linkers cleavable under different triggers and glyco-targeting with mannose. A synthetic pathway to stimuli responsive hyperbranched polyglycerol (hPG) porphyrin conjugates via the copper(I)-catalyzed 1,3-dipolar cycloaddition (CuAAC) or the strain-promoted alkyne-azide cycloaddition (SPAAC) has been developed. The PS 10,15,20-tris(3-hydroxyphenyl)-5-(2,3,4,5,6-pentafluorophenyl)porphyrin was functionalized with disulfide containing cystamine and acid-labile benzacetal linkers. Conjugates with reductively and pH labile linkers were thus obtained. Cleavage of the active PS agents from the polymer carrier is shown in several different release studies. The uptake of the conjugates into the cells is demonstrated via confocal laser scanning microscopy (CLSM) and flow cytometry. Finally, the antitumor and antibacterial phototoxicity of selected conjugates has been assessed in four different tumor cell lines and in cultures of the bacterium Staphylococcus aureus. The conjugates exhibited phototoxicity in several tumor cell lines in which conjugates with reductively cleavable linkers were more efficient compared to conjugates with acid-cleavable linkers. For S. aureus, strong phototoxicity was observed for a combination of the reductively cleavable and the pH labile linker and likewise for the cleavable conjugate with mannose targeting groups. The results thus suggest that the conjugates have potential for antitumor as well as antibacterial PDT.

Borondipyrrins (BODIPYs) have found wide-spread application in bioimaging and material sciences. These applications require the tuning of the chemical and photophysical properties of the fluorophore through the introduction of functional groups at the BODIPY core. In this context, an approach to bisfunctionalized BODIPYs has been explored. The oxidative nucleophilic substitution of hydrogen (ONSH) in the 3-(alpha)-position of BODIPYs has been combined with the nucleophilic substitution (SNAr) at the aryl unit of pentafluorophenyl (PFP)-substituted BODIPYs and their dipyrrane precursors. In an alternative approach, alpha-alkoxy-substituted BODIPYs have been prepared starting from the corresponding dipyrrin. In this case, the alpha-methoxy group of the BODIPY is susceptible to a hitherto unreported methoxy-amino exchange. The compounds were investigated with respect to their optical spectroscopic properties revealing the influence of the different substitution patterns on their absorption and emission spectra.

The use of carbohydrate thiolates for facile, high-yielding, regio- and stereoselective nucleophilic substitution reactions of complex pentafluorophenyl-substituted porphyrinoids is reported. The title reaction has successfully been applied to calix[4]phyrin, calix[6]phyrin, and [28]hexaphyrin substrates. The novel glycoporphyrinoid products with their extraordinary structures and unique photophysical properties are soluble in aqueous solutions and can serve as platforms for applications in biomedicine, catalysis, coordination, or redox chemistry.

The antibacterial photodynamic activity of hyperbranched polyglycerol (hPG) loaded with zinc porphyrin photosensitizers and mannose units was investigated. hPG, with a MW of 19.5 kDa, was functionalized with about 15 molecules of the photosensitizer {5,10,15-tris(3-hydroxyphenyl)-20-[4-(prop-2-yn-1-ylamino)tetrafluorophenyl]porphyrinato}-zinc(II) by using copper(I)-catalyzed 1,3-dipolar cycloaddition (CuAAC). These nanoparticle conjugates were functionalized systematically with increasing loadings of mannose in the range of approximately 20 to 110 groups. With higher mannose loadings (ca. 58–110 groups) the water-insoluble zinc porphyrin photosensitizer could thus be transferred into a water-soluble form. Targeting of the conjugates was proven in binding studies to the mannose-specific lectin concanavalin A (Con A) by using surface plasmon resonance (SPR). The antibacterial phototoxicity of the conjugates on Staphylococcus aureus (as a typical Gram-positive germ) was investigated in phosphate-buffered saline (PBS). It was shown that conjugates with approximately 70–110 mannose units exhibit significant antibacterial activity, whereas conjugates with approximately 20–60 units did not induce bacterial killing at all. These results give an insight into the multivalency effect in combination with photodynamic therapy (PDT). On addition of serum to the bacterial cultures, a quenching of this antibacterial phototoxicity was observed. In fluorescence studies with the conjugates in the presence of increasing bovine serum albumin (BSA) concentrations, protein-conjugate associations could be identified as a plausible cause for this quenching.

Limited drug penetration into tumor tissue is a significant factor to the effectiveness of cancer therapy. Tumor spheroids, a 3D cell culture model system, can be used to study drug penetration for pharmaceutical development. In this study, a method for quantitative bioimaging of platinum group elements by laser ablation (LA) coupled to inductively coupled plasma mass spectrometry (ICP-MS) is presented. Different matrix-matched standards were used to develop a quantitative LA-ICP-MS method with high spatial resolution. To investigate drug penetration, tumor spheroids were incubated with platinum complexes (Pt(II)acetylacetonate, cisplatin) and the palladium tagged photosensitizer 5,10,15,20-tetrakis(3-hydroxyphenyl)porphyrin (mTHPP). Distribution and accumulation of the pharmaceuticals were determined with the developed method.

Today, a growing number of nanotherapeutics is utilized to deliver poorly soluble compounds using the intravenous route of administration. The drug release and the direct transfer of the active pharmaceutical ingredient to serum proteins plays an important role in bioavailability and accumulation of the drug at the target site. It is closely related to the formation of a protein corona as well as the plasma protein binding of the compound. In the present study, two in vitro drug release methods, the flow-through cell and the dispersion releaser technology, were evaluated with regards to their capability to measure a time-resolved profile of the serum protein binding. In this context, the photosensitizer temoporfin and temoporfin-loaded liposomes were tested. While in the fine capillaries of the flow-through cell a rapid agglomeration of proteins occurred, the dispersion releaser technology in combination with the four-step model enabled the measurement of the transfer of drugs from liposomes to proteins. In presence of 10% of fetal calf serum approximately 20% of the model compound temoporfin were bound to serum proteins within the first 3 h. At higher serum concentration this binding remained stable for approximately 10 h.

Photodynamic therapy (PDT) is a well-established treatment option in the treatment of certain cancerous and pre-cancerous lesions. Though best-known for its application in tumor therapy, historically the photodynamic effect was first demonstrated against bacteria at the beginning of the 20th century. Today, in light of spreading antibiotic resistance and the rise of new infections, this photodynamic inactivation (PDI) of microbes, such as bacteria, fungi, and viruses, is gaining considerable attention. This review focuses on the PDI of viruses as an alternative treatment in antiviral therapy, but also as a means of viral decontamination, covering mainly the literature of the last decade. The PDI of viruses shares the general action mechanism of photodynamic applications: the irradiation of a dye with light and the subsequent generation of reactive oxygen species (ROS) which are the effective phototoxic agents damaging virus targets by reacting with viral nucleic acids, lipids and proteins. Interestingly, a light-independent antiviral activity has also been found for some of these dyes. This review covers the compound classes employed in the PDI of viruses and their various areas of use. In the medical area, currently two fields stand out in which the PDI of viruses has found broader application: the purification of blood products and the treatment of human papilloma virus manifestations. However, the PDI of viruses has also found interest in such diverse areas as water and surface decontamination, and biosafety.

Organic crystalline nanoparticles (NPs) are not fluorescent due to the crystalline structure of the flat molecules organized in layers. For Aluminum Phthalocyanine (AlPc)- derived NPs, preferential uptake and dissolution by macrophages were demonstrated recently. Therefore, inflamed tissue or cancer tissue with accumulated macrophages (M1; M2 polarization state) may exhibit specific fluorescence in contrast to normal tissue, which does not fluoresce. The present study addresses the photobiological effects of NP generated from the clinically utilized photosensitizer Temoporfin (mTHPC).

The monocyte/macrophage cell lineage reveals an enormous plasticity, which is required for tissue homeostasis, but is also undermined in various disease states, leading to a functional involvement of macrophages in major human diseases such as atherosclerosis and cancer. We recently generated in vivo evidence that crystalline, nonfluorescent nanoparticles of the hydrophobic porphyrin-related photosensitizer Aluminum phthalocyanine are selectively dissolved and thus may be used for specific fluorescent labelling of rejected, but not of accepted xenotransplants. This led us to hypothesize that nanoparticles made of planar photosensitizers such as porphyrins and chlorins were preferentially taken up and dissolved by macrophages, which was verified by in vitro studies. Here, using an in vitro system for macrophage differentiation/polarization of the human monocyte THP-1 cell line, we demonstrate differential uptake/dissolution of Temoporfin-derived nanoparticles in polarized macrophages, which resulted in differential photosensitivity. More importantly, low dose photodynamic sensitization using Temoporfin nanoparticles can be used to trigger M1 re-polarization of THP-1 cells previously polarized to the M2 state. Thus, sublethal photodynamic treatment using Temoporfin nanoparticles might be applied to induce a phenotypic shift of tumor-associated macrophages for the correction of an immunosuppressive microenvironment in the treatment of cancer, which may synergize with immune checkpoint inhibition.

A B S T R A C T The development and manufacture of novel nanocarriers for drug delivery has proved challenging with regards to scale-up and pharmaceutical quality. Polymeric nanocarriers composed of poly(lactic-coglycolic acid)-b-poly(ethylene glycol) (PLGA–PEG) were prepared and the photosensitizer meso-tetrakis (3-hydroxyphenyl) chlorin (mTHPC) was effectively encapsulated. Furthermore, the interplay of various process and formulation parameters and their impact on the most important product specifications were investigated by using a factorial design and a central composite design in a microfluidic manufacturing process. These nanoparticles for intravenous administration with a size of 97 � 0.13 nm, narrow size distribution, and an encapsulation efficiency of more than 80% were produced at high throughput. In vitro stability and in vitro drug release testing were applied for quality control purposes. Finally, the toxicity of the photosensitizer was tested in vitro. The cytotoxicity was successfully reduced while the efficacy of the formulation was maintained. First observations using in vivo imaging suggest effective distribution of the nanocarrier system after injection into rodents. Thus, further in vivo testing of the beneficial effects of nanoencapsulation into the matrix system and its formulation will be considered for the delivery of mTHPC to tumor tissues during photodynamic therapy.

The copper(I)-catalyzed 1,3-dipolar cycloaddition of 4-azido(tetrafluorophenyl)boron-dipyrrin (azido-BODIPY) with diverse terminal alkynes, varying from simple alkyl-substituted derivatives to alkynes with functional groups and carbohydrates, was successfully employed to obtain meso-functionalized BODIPY derivatives through the 1,2,3-triazole linkage. The scope of this reaction was extended to the preparation of di- and trivalent BODIPY systems through the use of appropriate alkynyl linkers. Moreover, the synthesis of hydroxyl- and pentafluorothio-(SF5)-substituted, 1,2,3-triazole-linked array systems consisting of porphyrins and corroles as the central scaffold, in combination with a BODIPY, was investigated. These covalently connected tetrapyrrole-BODIPY arrays exemplify a versatile approach to the construction of multichromophore systems: the combination of 1,3-dipolar cycloaddition and nucleophilic substitution on pentafluorophenyl-substituted porphyrinoids. The systems designed herein could serve in various light-harvesting applications and electron-transfer studies.

Chemistry - a European journal 24(4), 798-802 (2018). doi:10.1002/chem.201705206, Published by Wiley-VCH, Weinheim

A detailed study of the nucleophilic aromatic substitution reaction of meso-pentafluorophenyl-substituted tetrapyrrole systems with different alcohols is presented. The systematic investigation of various alcohols and bases in two different solvents led to optimized reaction conditions, allowing the selective substitution of the p-fluorine atoms of meso-pentafluorophenyl-substituted porphyrins, their zinc complexes, and a meso-tris(pentafluorophenyl)corrole with alcohols and a simple base in high yields. When applied to A3B porphyrins in combination with suitable protecting groups, functionalized, polar A3B porphyrins can be prepared in a simple two-step one-pot procedure. By using the nucleophilic aromatic substitution reaction, a dimeric porphyrin system was synthesized. In addition, the copper(I)-catalyzed 1,3-dipolar cycloaddition of properly functionalized meso-pentafluorophenyl-substituted porphyrins led to the corresponding porphyrin dimer with a 1,2,3-triazole linker. The method described herein allows a simple and fast approach towards multifunctionalized porphyrinoids based on meso-pentafluorophenyl-substituted tetrapyrroles.

International audience; To be effective anticancer drugs must penetrate tissue efficiently, reaching all target population of cancer cells in a concentration sufficient to exert a therapeutic effect. This study aimed to investigate the ability of methyl-β-cyclodextrin (Me-β-CD) and 2-hydroxypropyl-β-cyclodextrin (Hp-β-CD) to alter the penetration and diffusion of temoporfin (mTHPC) in HT29 multicellular tumor spheroids. mTHPC had а nonhomogenous distribution only on the periphery of spheroids. The presence of β-CDs significantly altered the distribution of mTHPC consisting in the increase of both the depth of photosensitizer penetration and accumulation in HT29 spheroids. We suggest that this improvement is related to the nanoshuttle mechanism of β-CD action, when β-CDs facilitate mTHPC transportation to the cells in the inner layers of spheroids. As a result of mTHPC distribution improvement, β-CDs enhance mTHPC photosensitizing activity towards HT29 multicellular tumor spheroids. The observed effects strongly depend on the type of β-CD. Thus, varying the type of β-CD we can finely tune the possibility of using mTHPC for diagnostic (delimitation of tumor margins) or therapeutic purposes.

The two-photon absorption of the photosensitizers 5,10,15,20-tetrakis( m -hydroxyphenyl) porphyrin and the corresponding chlorin has been studied in the near infrared (IR) range using open-aperture z -scan technique. We found cross sections of 10–40 GM in the Q-band region, comparable to values in the Soret-band. Both photosensitizers are promising candidates for IR two-photon photodynamic therapy given the better penetration of IR light into tissue.

meso-Substituted trans-A2B2-porphyrins bearing specific patterns of substituents are crucial building blocks in porphyrin-based biomimetic systems and molecular materials and can be used for the construction of well-defined porphyrin-based architectures. A new stepwise and rational synthesis of functionalized trans-A2B2-porphyrins is reported in which for the first time donor–acceptor-substituted cyclopropane precursors (d–a cyclopropanes) are exploited. The three presented d–a cyclopropanes are readily accessible in a multi-gram scale and serve as aldehyde equivalents in the reaction with an excess of pyrrole to afford the corresponding dipyrromethanes (DPMs). The three DPMs were synthesized in yields of 60–74%. They are stable in purified form in the absence of light and air and were subsequently condensed with a wide range of aliphatic and aromatic aldehydes bearing electron-donating or electron-withdrawing substituents followed by oxidation to form the corresponding trans-A2B2-porphyrins. Fourteen functionalized porphyrins were synthesized in yields of 14–31%, indicating the broad scope of the synthetic procedure. The possibility to introduce key functional groups is emphasized, which enables subsequent modification of these porphyrins with moieties inducing biological activity. Modification of the tetrapyrroles may occur by addition to one of the porphyrin peripheral double bonds, the use of substituents of the aryl groups or via the methoxycarbonyl group at two of the meso-substituents. Three examples of porphyrins were converted into the corresponding 7,8-dihydroxychlorins by osmium-mediated dihydroxylation and one of the resulting chlorins was subjected to saponification to give a highly polar chlorin dicarboxylic acid. A 4-bromophenyl-substituted d–a cyclopropane was prepared by rhodium-catalyzed cyclopropanation and then transformed into a DPM which was subsequently condensed to a porphyrin. Its Zn complex allowed a Heck reaction to afford the functionalized bis(alkenyl)-substituted trans-A2B2-Zn-porphyrin.

Congest and conjugate: The application of a sterically congested dipyrromethane in an acid-catalyzed [2+2+2] building-block approach was studied for the first time, resulting in the formation of two stable calix[6]phyrin(1.1.1.1.1.1) diastereomers (see scheme). The calix[n]phyrins were further functionalized at their pentafluorophenyl residues, allowing the first synthesis of a calix[4]phyrin(1.1.1.1) dimer.

The reaction of amines with pentafluorophenyl-substituted A3B-porphyrins has been used to obtain different useful reactive groups for further functionalization and/or conjugation of these porphyrins to other substrates or materials. Porphyrins with alkenyl, alkynyl, amino, azido, epoxide, hydroxyl, and maleimido groups have thus been synthesized. For the first time such functionalized porphyrins have been conjugated to hyperbranched polyglycerol (hPG) as a biocompatible carrier system for photodynamic therapy (PDT) using the copper(I)-catalyzed 1,3-dipolar cycloaddition (CuAAC). The photocytotoxicity of selected porphyrins as well as of the porphyrin-hPG- conjugates has been assessed in cellular assays with human epidermoid carcinoma A-253 and squamous carcinoma CAL-27 cells. For several biomedical applications a release of the active drug and/or fluorescent dye is desired. Therefore, additionally, the synthesis of A3B-porphyrins with cleavable linker moieties is presented, namely disulfide, cleavable in a reductive environment, and acetal linkers whose cleavage is pH triggered.

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 (SN 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.

Calix[4]phyrins are an important class of hybrid macrocyclic systems at the interface between porphyrins and calixpyrroles (porphyrinogens). A new stepwise synthesis of oxidation-resistant meso-hydrogenated calix[4]phyrins is reported, which allows variable substitution in the residues of their sp2-meso-centers without the need for a porphyrin intermediate. It relies on the acid-catalyzed condensation of a sterically hindered donor–acceptor-substituted cyclopropane precursor with pyrrole to form a sterically congested dipyrromethane. This was subsequently condensed with a wide range of alkyl and aryl aldehydes bearing electron-donating or electron-withdrawing substituents followed by an oxidation step to form stable calix[4]phyrin(1.1.1.1)s with bridging meso-CH hydrogen atoms through an acid-promoted dehydrative condensation. The methodology avoids any need for premetallation of the macrocycle and/or the use of organometallic catalysts or reagents and allows the incorporation of the bulky cyclopropane-derived substituents specifically into the 5,15-meso-like positions. The resulting regioisomerically pure products display conformational features that reflect their mixed nature between porphyrins and calixpyrroles and they were assessed by X-ray diffraction analysis, NMR techniques and UV/Vis spectroscopy. The possibility to introduce key functional groups enables subsequent modification of these calix[4]phyrins and allows their connection to other groups such as biologically active moieties. Of special interest is an unprecedented example of an acid-driven lactonization that results in the incorporation of a mono-meso-spirolactone into a calix[4]phyrin(1.1.1.1). Moreover, it is demonstrated that this approach to calix[4]phyrins is also applicable to other sterically congested dipyrromethanes.

The trichloroacetimidate method has been utilized for the glycosylation of porphyrins. The corresponding glycoconjugates were obtained rapidly, in high yields, and excellent purity. A three-step sequence using well-matched (Lewis) acids was found to be highly effective and reliable.

Calcium phosphate nanoparticles were surface-functionalized with different polymers, and photosensitizers were incorporated into this layer. The charge was adjusted by choosing the appropriate polymer. Methylene blue and 5,10,15,20-tetrakis(3-hydroxyphenyl)porphyrin (mTHPP) were used as photosensitizers. The particles showed a good performance with HIG-82 synoviocytes. For J774A.1 macrophages, they were toxic also in the dark, probably due to a lethal uptake of calcium. For HT29 epithelial cells, a moderate activity was observed. A good photoxicity was observed against the bacterial strain Staphylococcus aureus (Gram-positive), both with positively and negatively charged nanoparticles loaded with mTHPP. Against Pseudomonas aeruginosa (Gram-negative), good photoxicity was observed only with positively charged nanoparticles loaded with mTHPP. At higher concentrations, methylene blue-loaded nanoparticles were active against S. aureus. Thus, it is possible to prepare a water-dispersable system of dye-loaded calcium phosphate nanoparticles, but the efficiency depends on a number of parameters, e.g. particle charge, kind of polymer, and cell culture medium (e.g. the presence of proteins).

The reaction of alcohols with (pentafluorophenyl)dipyrromethane (PFP-DPM) under basic conditions has been studied, giving access to the corresponding alkoxy-substituted DPMs. This method represents the first high-yielding substitution of PFP-DPM carried out with oxygen nucleophiles. Condensation of these prefunctionalized DPMs with aldehydes led to the respective trans-A2B2 porphyrins. This pathway allows a simple synthesis of multifunctionalized tetrapyrroles. Oxidation and boron complexation of these DPMs, on the other hand, led to meso-functionalized difluoroboraindacenes (BODIPYs). In addition, nucleophilic substitution of PFP-BODIPY with sodium azide led to a 4-azidophenyl derivative, thus further enhancing the scope of reactive sites suitable for subsequent transformations.

The synthesis of novel pentafluorosulfanyl (SF5)-substituted A4-type porphyrins, their corresponding Zn(II)- and Pd(II)-metal complexes, A3-, A2B- and AB2-type corroles, BODIPYs, and their dipyrrane precursors was studied utilizing commercially available SF5-substituted aryl aldehydes. In addition, the functionalization of SF5-substituted tetrapyrroles was investigated by applying the concept of the nucleophilic aromatic substitution (S(N)Ar) with alcohols and sodium azide onto the pentafluorophenyl moiety of a trans-A2B2-porphyrin and two corrole derivatives with a mixed substitution pattern involving the SF5 group. This allows a fine-tuning of the properties of these macrocycles through a selective and mild introduction of functional groups, giving access to multifunctionalized SF5-substituted porphyrinoids. As an example, one functionalized corrole was further reacted with an azido-substituted BODIPY via the copper(I)-catalyzed 1,3-dipolar cycloaddition yielding the first corrole-BODIPY heterodimer involving the pentafluorosulfanyl group.

Photodynamic therapy (PDT) is a developing modality for the treatment of certain tumorous and other diseases. Considerable progress has been made in recent years in the search for new photosensitizers, in particular elucidating the role of localization of the photosensitizer. Known successful photosensitizers of the tetrapyrrole type are amphiphilic molecules, preferably localizing in cellular membrane structures. Thus, the quest for new photosensitizers requires the synthesis of unsymmetrically Substituted (amphiphilic) tetrapyrroles. In this article. we describe strategies for the de novo synthesis of amphiphilic tetrapyrroles using a 3-hydroxyphenyl substituted tetrapyrrolic system (Temoporfin) as the lead structure. From an applied science-oriented approach, such a set of amphiphilic porphyrins is best synthesized by combining well-developed condensation methods with subsequent functionalization via organolithium compound or transition metal catalyzed coupling protocols. Starting from simple A(2)- or AB-porphyrins, the synthesis of A(2)B-, A(3)-, A(3)B-, and A(2)BC-porphyrins with a mixed hydrophilic/hydrophobic substitution pattern is described. Because of the versatility of this approach to unsymmetrically Substituted porphyrins it is also applicable to other areas where porphyryns with a tailor-made substitution patterns are needed. for example. catalysts or molecular electronic devices based on tetrapyrroles. (c) 2005 Elsevier Ltd. All rights reserved

General syntheses have been developed for meso-substituted por- phyrins with one or two substituents in the 5,10-positions and no b substitu- ents. 5-Substituted porphyrins with only one meso substituent are easily prepared by an acid-catalyzed conden- sation of dipyrromethane, pyrrole-2- carbaldehyde, and an appropriate alde- hyde using a "(2+1+1)" approach. Sim- ilarly, 5,10-disubstituted porphyrins are accessible by simple condensation of unsubstituted tripyrrane with pyrrole and various aldehydes using a "(3+1)" approach. The yields for these reac- tions are low to moderate and addi- tional formation of either di- or mono- substituted porphyrins due to scram- bling of the intermediates is observed. However, the reactions can be per- formed quite easily and the desired target compounds are easily removed due to large differences in solubility. A complementary and more selective syn- thesis involves the use of organolithium reagents for SNAr reactions. Reaction of in situ generated porphyrin (por- phine) with 1.1-8 equivalents of RLi gave the monosubstituted porphyrins, while reaction with 3-6 equivalents of RLi gave the 5,10-disubstituted por- phyrins in yields ranging from 43 to 90 %. These hitherto almost inaccessi- ble compounds complete the series of different homologues of A-, 5,15-A2-, 5,10-A2-, A3-, and A4-type porphyrins and allow an investigation of the grad- ual influence of type, number, and re- giochemical arrangement of substitu- ents on the properties of meso-substi- tuted porphyrins. They also present im- portant starting materials for the syn- thesis of ABCD porphyrins and are potential synthons for supramolecular materials requiring specific substituent orientations.

The search for new efficient sensitizers for photodynamic therapy (PDT) points to improve photophysical properties like absorption in the red region and singlet oxygen quantum yield as well as to control the localization of the sensitizer within the tumour cell. Depending on their physicochemical properties and their uptake mechanism, sensitizers can reach different intracellular concentrations and localize in different subcellular compartments. Moreover, the preferential localization of a sensitizer in target organelles, like mitochondria or lysosomes, could determine the cell death mechanism after PDT. This study aimed to investigate the influence of substitutions on dihydroxychlorins with regard to intracellular uptake, subcellular localization and cell death pathway. Moreover, the effect of a liposome-based delivery system was tested. The intracellular uptake was found to be strictly dependent on the sensitizer molecular structure and the means of its delivery. The most polar sensitizer in this study (compound 3) had, depending on incubation time, an intracellular concentration 2-8 times higher than the unsubstituted chlorin 1. All investigated photosensitizers localize predominantly in lysosomes but after longer incubation times weak fluorescence intensity was also detected in mitochondria and Golgi apparatus. The cell death pathway was found to be influenced by the sensitizer intracellular concentration and the applied light doses. In general, the increasing amphiphilicity of the sensitizer molecules is correlated with an increased sensitizer uptake and an increased rate of necrotic cells after irradiation. (C) 2004 Elsevier B.V. All rights reserved

The reaction of alcohols with (pentafluorophenyl)dipyrromethane (PFP-DPM) under basic conditions has been studied, giving access to the corresponding alkoxy-substituted DPMs. This method represents the first high-yielding substitution of PFP-DPM carried out with oxygen nucleophiles. Condensation of these prefunctionalized DPMs with aldehydes led to the respective trans-A2B2 porphyrins. This pathway allows a simple synthesis of multifunctionalized tetrapyrroles. Oxidation and boron complexation of these DPMs, on the other hand, led to meso-functionalized difluoroboraindacenes (BODIPYs). In addition, nucleophilic substitution of PFP-BODIPY with sodium azide led to a 4-azidophenyl derivative, thus further enhancing the scope of reactive sites suitable for subsequent transformations.

Industrial production of nanosized drug delivery devices is still an obstacle to the commercialization of nanomedicines. This study encompasses the development of nanoparticles for peroral application in photodynamic therapy, optimization according to the selected product specifications, and the translation into a continuous flow process. Polymeric nanoparticles were prepared by nanoprecipitation of Eudragit® RS 100 in presence and in absence of glycofurol. The photosensitizer temoporfin has been encapsulated into these carrier devices. Process parameters were optimized by means of a Design of Experiments approach and nanoparticles with optimal characteristics were manufactured by using microreactor technology. The efficacy was determined by means of cell culture models in A-253 cells. Physicochemical properties of nanoparticles achieved by nanoprecipitation from ethanolic solutions were superior to those obtained from a method based upon glycofurol. Nanoencapsulation of temoporfin into the matrix significantly reduced toxicity of this compound, while the efficacy was maintained. The release profiles assured a sustained release at the site of action. Finally, the transfer to continuous flow technology was achieved. By adjusting all process parameters, a potent formulation for application in the GI tract was obtained. The essential steps of process development and scale-up were part of this formulation development.

The photodynamic therapy (PDT) related photophysical properties of five palladium(II) porphyrins with increasing steric demand of the meso-substituents were investigated by steady state and time-resolved absorption and luminescence spectroscopy. The steric strain of the meso-substituents is reflected in a bathochromic shift of the B-band in the absorption spectra. In contrast to free-base porphyrins, the palladium(II) complexes exhibit only a very weak fluorescence with Φ Fl ~ 10-4. Instead, the corresponding triplet states of the porphyrins are formed via inter system crossing (ISC) with a quantum yield ΦISC of nearly unity. A phosphorescence quantum yield ΦISC of 10-4 was determined assuming dynamic quenching. The triplet state of all compounds is efficiently quenched by molecular oxygen, generating singlet molecular oxygen with a quantum yield of ΦΔ ~ 0.85. The various substitution patterns exerted no significant influence on the ISC rates or singlet oxygen quantum yields. Significant differences, on the other hand, were observed with respect to the triplet lifetimes, with a tendency of longer lifetimes for the porphyrins with sterically more demanding substituents (in air-saturated solution). All porphyrins were successfully incorporated into liposomes. The phototoxic activity of three compounds was investigated in cell suspensions. The use of the new porphyrinato-palladium(II) in PDT applications is discussed.

Rigidly and covalently linked porphyrin quinones are well established as model compounds for studying photo-induced electron transfer (PET) reactions like those occurring during the primary processes of photosynthesis. In this context, the synthesis of a number of porphyrin quinones is reported in which one or two porphyrin electron donors are connected to either one or two quinone electron acceptors, resulting in diad, triad, and tetrad model systems, respectively. The porphyrin(s) and the quinone(s) are linked by triptycene, 1,4-phenylene, and cis- or trans-1,4-cyclohexylene bridges. The use of the 1,4-phenylene, and cis- or trans-1,4-cyclohexylene bridges results in donor–acceptor compounds with the same number of bonds between donor and acceptor(s), but differing in distance and orientation. Analysis of the 1H NMR spectra confirmed the chair conformation for the cis- and trans-cyclohexylene-linked diads and triads. NOE experiments gave information about the spatial arrangement of the target compounds. The key compounds in the syntheses of all these new PET model systems are the triptycene quinones, which are formed via a [πs4+πs2]-cycloaddition between an anthracene derivative and a suitable quinone. The triptycene system enforces a rigid orientation on the quinone acceptor(s) in the final model system. Evidence is given that the triptycene system has further potential for constructing tailor-made donor–acceptor compounds.

Photoinduced intramolecular electron transfer was studied by time-resolved electron paramagnetic resonance spectroscopy in two photosynthetic model systems oriented in a nematic liquid crystal. The donor−acceptor assemblies consisted of differently substituted zinc porphyrins covalently linked to a quinone with different spacers, i.e., triptycyl and cyclohexylene. The orientation of the guest molecules with respect to the director of the liquid crystal was determined by line shape analysis of their triplet spectra and by molecular modeling. It is demonstrated that the polarized pattern of the radical pair spectrum is sensitive mainly to the spacer structure, but to some extent also to the peripheral substituents.

A total of 21 different porphyrins, some of them closely related to the photosensitizer meta-tetrahydroxyphenylchlorin (m-THPC) with a varied degree of hydrophilic/lipophilic substitution were synthesized employing conventional porphyrin condensation procedures and modern functionalization via organolithium reagents. For 14 of them, the photodynamic therapy (PDT) related photophysical properties were determined in isotropic solution and in liposome membrane-model systems. The photophysical data indicate that the localization of m-THPC may be fine-tuned by carefully changing the substitution pattern.

Dendrimers are very promising molecules as hosts for guest embedding as well as for multiple covalent coupling of dye molecules to their peripheral groups. The use of such dendrimer–dye conjugates as part of a modular carrier system for photodynamic therapy has recently been discussed. Using covalent coupling we accomplished an average loading of 12–13 molecules of pheophorbide a to one diaminobutane poly-propylene-imine dendrimer molecule of the third generation (DAB dendrimer) having a total number of 16 binding sites. This was confirmed with various photophysical measurements and MALDI-mass spectrometry. As long as the dye molecules are covalently bound to the dendrimer, their photosensitized generation of singlet oxygen is reduced dramatically due to interactions between different dye molecules. The main interaction is supposed to be a Forster-energy transfer along the surface of the dendrimer–dye complex. Nevertheless the remaining photosensitized generated singlet oxygen leads to a destruction of the dendrimer backbone under illumination. The photophysical properties of the covalently linked dye–dendrimer complexes and especially the remarkable influence of illumination on these properties are presented in this paper.