Chemical Synthesis and Medicinal Applications of Glycoporphyrins

De Novo Access to BODIPY C-Glycosides as Linker-Free Nonsymmetrical BODIPY-Carbohydrate Conjugates

Recent years have witnessed an increasing interest in the synthesis and study of BODIPY-glycoconjugates. Most of the described synthetic methods toward these derivatives involve postfunctional modifications of the BODIPY core followed by the covalent attachment of the fluorophore and the carbohydrate through a "connector". Conversely, few de novo synthetic approaches to linker-free carbohydrate-BODIPY hybrids have been described. We have developed a reliable modular, de novo, synthetic strategy to linker-free BODIPY-sugar derivatives using the condensation of pyrrole C-glycosides with a pyrrole-carbaldehyde derivative mediated by POCl3. This methodology allows labeling of carbohydrate biomolecules with fluorescent-enough BODIPYs within the biological window, stable in aqueous media, and able to display singlet oxygen generation.

Targeted photodynamic therapy for breast cancer: the potential of glyconanoparticles

Photodynamic therapy (PDT) uses a non-toxic light sensitive molecule, a photosensitiser, that releases cytotoxic reactive oxygen species upon activation with light of a specific wavelength. Here, glycan-modified 16 nm gold nanoparticles (glycoAuNPs) were explored for their use in targeted PDT, where the photosensitiser was localised to the target cell through selective glycan-lectin interactions. Polyacrylamide (PAA)-glycans were chosen to assess glycan binding to the cell lines. These PAA-glycans indicated the selective uptake of a galactose-derivative PAA by two breast cancer cell lines, SK-BR-3 and MDA-MD-231. Subsequently, AuNPs were modified with a galactose-derivative ligand and an amine derivate of the photosensitiser chlorin e6 was incorporated to the nanoparticle surface via amide bond formation using EDC/NHS coupling chemistry. The dual modified nanoparticles were investigated for the targeted cell killing of breast cancer cells, demonstrating the versatility of using glycoAuNPs for selective binding to different cancer cells and their potential use for targeted PDT.

Doubly Stimulated Corrole for Organelle-Selective Antitumor Cytotoxicity

Balancing between safety and efficacy of cancer chemotherapeutics is achievable by relying on internal and/or external stimuli for selective and on-demand antitumor cytotoxicity. We now introduce the difluorophosphorus(V) corrole PC-Im, a theranostic agent with a pH-sensitive N-methylimidazole moiety. Structure/activity relationships, via comparison with the permanently charged PC-ImM+ and the lipophilic PC, uncovered the exceptional features of PC-Im: nanoparticular and monomeric at neutral and low pH, respectively, 10-fold increased light-induced singlet oxygen production at acidic pH, internalization into malignant cells within minutes, and selective accumulation within lysosomes. Submillimolar PC-Im concentrations are tolerable in the dark, while illumination induces nanomolar cytotoxic effects due to a multiplicity of cellular deleterious events: endoplasmic reticulum fragmentation, lysosome fusion and exocytosis, calcium leakage, mitochondrial fission, and swelling. PC-Im emerges as an antitumor agent, whose potency is triggered by endogenous and exogenous stimuli, assuring its cytotoxicity will occur selectively upon lysosomal accumulation and solely upon light activation.

Photosensitized Oxidation of Intracellular Targets: Understanding the Mechanisms to Improve the Efficiency of Photodynamic Therapy

The development of improved photosensitizers is a key aspect in the establishment of photodynamic therapy (PDT) as a reliable treatment modality. In this chapter, we discuss how molecular design can lead to photosensitizers with higher selectivity and better efficiency, with focus on the importance of specific intracellular targeting in determining the cell death mechanism and, consequently, the PDT outcome.

Meso-tetra(dioxanyl)porphyrins: Neutral, low molecular weight, and chiral porphyrins with solubility in aqueous solutions

The synthesis of the low-molecular weight, meso-tetra(dioxan-2-yl)porphyrin with considerable solubility in aqueous solution is described. The key intermediate dioxan-2-carbaldehyde is accessible in either racemic or in stereo-pure forms from commercially available starting materials in three steps. Using 4 × 1 or 2 + 2-type syntheses provide the porphyrin in modest yields. While the racemic aldehyde created an intractable mixture of diastereomers, the enantiopure aldehyde created a single enantiomer of the target porphyrin. The porphyrin was spectroscopically characterized. As its free base or zinc complex, it showed excellent solubility properties in organic and aqueous solvents, though free water-solubility was not achieved. The work expands on the availability of chiral porphyrins and neutral porphyrins with considerable solubility in aqueous solution.

Nucleophilic Aromatic Substitution (SNAr) and Related Reactions of Porphyrinoids: Mechanistic and Regiochemical Aspects

The nucleophilic substitution of aromatic moieties (SNAr) has been known for over 150 years and found wide use for the functionalization of (hetero)aromatic systems. Currently, several "types" of SNAr reactions have been established and notably the area of porphyrinoid macrocycles has seen many uses thereof. Herein, we detail the SNAr reactions of seven types of porphyrinoids with differing number and type of pyrrole units: subporphyrins, norcorroles, corroles, porphyrins, azuliporphyrins, N-confused porphyrins, and phthalocyanines. For each we analyze the substitution dependent upon: a) the type of nucleophile and b) the site of substitution (α, β, or meso). Along with this we evaluate this route as a synthetic strategy for the generation of unsymmetrical porphyrinoids. Distinct trends can be identified for each type of porphyrinoid discussed, regardless of nucleophile. The use of nucleophilic substitution on porphyrinoids is found to often be a cost-effective procedure with the ability to yield complex substituent patterns, which can be conducted in non-anhydrous solvents with easily accessible simple porphyrinoids.

Metallotherapeutics development in the age of iron-clad bacteria

Drug-resistant infections pose a significant risk to global health as pathogenic bacteria become increasingly difficult to treat. The rapid selection of resistant strains through poor antibiotic stewardship has reduced the number of viable treatments and increased morbidity of infections, especially among the immunocompromised. To circumvent such challenges, new strategies are required to stay ahead of emerging resistance trends, yet research and funding for antibiotic development lags other classes of therapeutics. Though the use of metals in therapeutics has been around for centuries, recent strategies have devoted a great deal of effort into the pathways through which bacteria acquire and utilize iron, which is critical for the establishment of infection. To target iron uptake systems, siderophore-drug conjugates have been developed that hijack siderophore-based iron uptake for delivery of antibiotics. While this strategy has produced several potential leads, the use of siderophores in infection is diminished over time when bacteria adapt to utilize heme as an iron source, leading to a need for the development of porphyrin mimetics as therapeutics. The use of such strategies as well as the inclusion of gallium, a redox-inert iron mimic, are herein reviewed.

Anti-angiogenic and anti-inflammatory activity of the summer truffle (Tuber aestivum Vittad.) extracts and a correlation with the chemical constituents identified therein

Fungi are a huge source of unexplored bioactive compounds. Owing to their biological activities, several fungi have shown commercial application in the health industry. Tuber aestivum Vittad. is one such edible fungi with an immense scope for practical biological applications. In the present study, the anti-angiogenic activity of petroleum ether and ethanol extracts of T. aestivum was investigated using the chick chorioallantoic membrane assay and compared to the positive controls silibinin and lenalidomide. Both the extracts showed a dose-dependent anti-angiogenic response. The extracts were also assessed for their anti-inflammatory potential by lipoxygenase-inhibition assay. The IC₅₀ values for LOX inhibition assay, computed by the Boltzmann plot, were 368.5, 147.3 and 40.2 µg/mL, for the petroleum ether extract, ethanol extract, and the positive control ascorbic acid, respectively. The ethanol extract of T. aestivum showed superior anti-angiogenic and anti-inflammatory activity than the petroleum ether extract. Compositional investigation of the extracts by GC-MS revealed the presence of various bioactive compounds. The compounds were correlated to their anti-angiogenic and anti-inflammatory activity based on a meticulous literature search.

Fluorescent supramolecular hierarchical self-assemblies from glycosylated 4-amino- and 4-bromo-1,8-naphthalimides

The investigation into the self-assembly formation of the glycan based 4-amino- and 4-bromo-1,8-naphthalimide (Nap) structures1–3is presented.

Synthesis of Porphyrin and Bacteriochlorin Glycoconjugates through CuAAC Reaction Tuning

Rapid and reproducible access to a series of unique porphyrin and bacteriochlorin glycoconjugates, including meso-glycosylated porphyrins and bacteriochlorins, and beta-glycosylated porphyrins, via copper catalyzed azide-alkyne 1,3-dipolar cycloaddition (CuAAC) is reported for the first time. The work presented highlights the system-dependent reaction conditions required for glycosylation to porphyrins and bacteriochlorins based on the unique electronic properties of each ring system. Attenuated reaction conditions were used to synthesize fifteen new glycosylated porphyrin and bacteriochlorin analogs in 74 - 99% yield, and were extended to solid support to produce the first oligo(amidoamine)-based porphyrin glycoconjugate. These compounds hold significant potential as next generation water soluble catalysts and photodynamic therapy/photodynamic inactivation (PDT/PDI) agents.

Hydrogels: soft matters in photomedicine

Photodynamic therapy (PDT), a shining beacon in the realm of photomedicine, is a non-invasive technique that utilizes dye-based photosensitizers (PSs) in conjunction with light and oxygen to produce reactive oxygen species to combat malignant tissues and infectious microorganisms. Yet, for PDT to become a common, routine therapy, it is still necessary to overcome limitations such as photosensitizer solubility, long-term side effects (e.g., photosensitivity) and to develop safe, biocompatible and target-specific formulations. Polymer based drug delivery platforms are an effective strategy for the delivery of PSs for PDT applications. Among them, hydrogels and 3D polymer scaffolds with the ability to swell in aqueous media have been deeply investigated. Particularly, hydrogel-based formulations present real potential to fulfill all requirements of an ideal PDT platform by overcoming the solubility issues, while improving the selectivity and targeting drawbacks of the PSs alone. In this perspective, we summarize the use of hydrogels as carrier systems of PSs to enhance the effectiveness of PDT against infections and cancer. Their potential in environmental and biomedical applications, such as tissue engineering photoremediation and photochemistry, is also discussed.

Trends and targets in antiviral phototherapy

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 20^th 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.

Nucleophilic Thioglycosylation of Pentafluorophenyl-Substituted Porphyrinoids: Synthesis of Glycosylated Calix[n]phyrin and [28]Hexaphyrin Systems

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.

Functional Supramolecular Gels Based on the Hierarchical Assembly of Porphyrins and Phthalocyanines

Supramolecular gels containing porphyrins and phthalocyanines motifs are attracting increased interests in a wide range of research areas. Based on the supramolecular gels systems, porphyrin or phthalocyanines can form assemblies with plentiful nanostructures, dynamic, and stimuli-responsive properties. And these π-conjugated molecular building blocks also afford supramolecular gels with many new features, depending on their photochemical and electrochemical characteristics. As one of the most characteristic models, the supramolecular chirality of these soft matters was investigated. Notably, the application of supramolecular gels containing porphyrins and phthalocyanines has been developed in the field of catalysis, molecular sensing, biological imaging, drug delivery and photodynamic therapy. And some photoelectric devices were also fabricated depending on the gelation of porphyrins or phthalocyanines. This paper presents an overview of the progress achieved in this issue along with some perspectives for further advances.

Cell-Penetrating Protein/Corrole Nanoparticles

Recent work has highlighted the potential of metallocorroles as versatile platforms for the development of drugs and imaging agents, since the bioavailability, physicochemical properties and therapeutic activity can be dramatically altered by metal ion substitution and/or functional group replacement. Significant advances in cancer treatment and imaging have been reported based on work with a water-soluble bis-sulfonated gallium corrole in both cellular and rodent-based models. We now show that cytotoxicities increase in the order Ga < Fe < Al < Mn < Sb < Au for bis-sulfonated corroles; and, importantly, that they correlate with metallocorrole affinities for very low density lipoprotein (VLDL), the main carrier of lipophilic drugs. As chemotherapeutic potential is predicted to be enhanced by increased lipophilicity, we have developed a novel method for the preparation of cell-penetrating lipophilic metallocorrole/serum-protein nanoparticles (NPs). Cryo-TEM revealed an average core metallocorrole particle size of 32 nm, with protein tendrils extending from the core (conjugate size is ~100 nm). Optical imaging of DU-145 prostate cancer cells treated with corrole NPs (≤100 nM) revealed fast cellular uptake, very slow release, and distribution into the endoplasmic reticulum (ER) and lysosomes. The physical properties of corrole NPs prepared in combination with transferrin and albumin were alike, but the former were internalized to a greater extent by the transferrin-receptor-rich DU-145 cells. Our method of preparation of corrole/protein NPs may be generalizable to many bioactive hydrophobic molecules to enhance their bioavailability and target affinity.

Molecular Engineering of Free-Base Porphyrins as Ligands-The N-H⋅⋅⋅X Binding Motif in Tetrapyrroles

The core N-H units of planar porphyrins are often inaccessible to forming hydrogen-bonding complexes with acceptor molecules. This is due to the fact that the amine moieties are "shielded" by the macrocyclic system, impeding the formation of intermolecular H-bonds. However, methods exist to modulate the tetrapyrrole conformations and to reshape the vector of N-H orientation outwards, thus increasing their availability and reactivity. Strategies include the use of porpho(di)methenes and phlorins (calixphyrins), as well as saddle-distorted porphyrins. The former form cavities due to interruption of the aromatic system. The latter are highly basic systems and capable of binding anions and neutral molecules via N-H⋅⋅⋅X-type H-bonds. This Review discusses the role of porphyrin(oid) ligands in various coordination-type complexes, means to access the core for hydrogen bonding, the concept of conformational control, and emerging applications, such as organocatalysis and sensors.

Glycosylated naphthalimides and naphthalimide Tröger's bases as fluorescent aggregation probes for Con A

We report the synthesis of glycosylated naphthalimide compounds and their application as fluorescent probes for Concanavalin A (Con A) lectin.

Pre-/post-functionalization in dipyrrin metal complexes - antitumor and antibacterial activity of their glycosylated derivatives

A post-functionalization route to tris(dipyrrinato) metal complexes is presented giving access to a range of new complexes relevant in the context of medicinal inorganic chemistry. A pentafluorophenyl group in the meso-position of the dipyrrin ligand serves as an anchor for the connection with alcohols and thiocarbohydrates. The photochemotherapeutic activity of the complexes has been assessed in cellular assays with tumor cell lines and against the Gram-positive bacterium S. aureus. Finally, it is shown that this post-functionalization is also applicable to other dipyrrinato metal complexes.

The development of ruthenium(ii) polypyridyl complexes and conjugates for in vitro cellular and in vivo applications

Ruthenium(ii) [Ru(ii)] polypyridyl complexes have been the focus of intense investigations since work began exploring their supramolecular interactions with DNA. In recent years, there have been considerable efforts to translate this solution-based research into a biological environment with the intention of developing new classes of probes, luminescent imaging agents, therapeutics and theranostics. In only 10 years the field has expanded with diverse applications for these complexes as imaging agents and promising candidates for therapeutics. In light of these efforts this review exclusively focuses on the developments of these complexes in biological systems, both in cells and in vivo, and hopes to communicate to readers the diversity of applications within which these complexes have found use, as well as new insights gained along the way and challenges that researchers in this field still face.

A glycoporphyrin story: from chemistry to PDT treatment of cancer mouse models

Glycoporphyrin: from bench to preclinical studies on PDX xenografted on mice.

Trace Oxygen Sensitive Material Based on Two Porphyrin Derivatives in a Heterodimeric Complex

The successful preparation of a novel dimer complex formed between 5,10,15,20-tetrakis(3,4-dimethoxyphenyl)-porphyrin Fe(III) chloride and (5,10,15,20-tetraphenylporphinato) dichlorophosphorus(V) chloride using the well-known reactivity of the P-X bond is reported. The obtained complex was characterized by UV-vis, Fourier transform infrared spectroscopy (FT-IR), fluorescence, ¹H-NMR, ¹³C-NMR, and ³¹P-NMR spectroscopic techniques and also by additional Heteronuclear Single Quantum Coherence (HSQC) and Heteronuclear Multiple Bond Correlation (HMBC) experiments in order to correctly assign the NMR signals. Scanning electron microscopy (SEM) and EDX quantifications completed the characterizations. This novel porphyrin dimer complex demonstrated fluorescence sensing of H₂O₂ in water for low oxygen concentrations in the range of 40-90 µM proving medical relevance for early diagnosis of diseases such as Alzheimer's, Parkinson's, Huntington's, and even cancer because higher concentrations of H₂O₂ than 50 μM are consideredcytotoxic for life. Due to its optical properties, this novel metalloporphyrin-porphyrin based complex is expected to show PDT and bactericidal activity under visible-light irradiation.

Modifications of Porphyrins and Hydroporphyrins for Their Solubilization in Aqueous Media

The increasing popularity of porphyrins and hydroporphyrins for use in a variety of biomedical (photodynamic therapy, fluorescence tagging and imaging, photoacoustic imaging) and technical (chemosensing, catalysis, light harvesting) applications is also associated with the growing number of methodologies that enable their solubilization in aqueous media. Natively, the vast majority of synthetic porphyrinic compounds are not water-soluble. Moreover, any water-solubility imposes several restrictions on the synthetic chemist on when to install solubilizing groups in the synthetic sequence, and how to isolate and purify these compounds. This review summarizes the chemical modifications to render synthetic porphyrins water-soluble, with a focus on the work disclosed since 2000. Where available, practical data such as solubility, indicators for the degree of aggregation, and special notes for the practitioner are listed. We hope that this review will guide synthetic chemists through the many strategies known to make porphyrins and hydroporphyrins water soluble.

Beryllium subphthalocyanines self-assembling properties

Beryllium subphthalocyanines have been recently shown to be suitable candidates for photochemical devices if combined with appropriate donor systems. The ability of beryllium subphthalocyanines to self-assemble is explored for the first time by means of density functional theory calculations. Free dimers of beryllium subphtalocyanine and their corresponding complexes with water and pyridine are computed at the wB97X-D/6-311+G(d,p) level of theory. In contrast with the behavior reported for beryllium phthalocyanines, for beryllium subphtalocyanines, beryllium–aza–nitrogen intermolecular interactions are observed, suggesting that these species are likely to self-assemble. Aggregates of related structures such as beryllium subporphyrazines with axial groups confirm the importance of hydrogen bonds in the stacking.

Glycosidase activated release of fluorescent 1,8-naphthalimide probes for tumor cell imaging from glycosylated 'pro-probes'

Glycosylated 4-amino-1,8-naphthalimide derivatives possess a native glycosidic linkage that can be selectively hydrolysed in situ by glycosidase enzymes to release the naphthalimide as a fluorescent imaging or therapeutic agent. In vitro studies using a variety of cancer cell lines demonstrated that the naphthalimides only get taken up into cells upon enzymatic cleavage from the glycan unit; a mechanism that offers a novel approach for the targeted delivery of probes/drugs.

Solid-Supported Porphyrins Useful for the Synthesis of Conjugates with Oligomeric Biomolecules

meso-Tris(pyridin-4-yl)(4-carboxyphenyl)porphyrin and 2-(1-hexyloxyethyl)-2-devinyl pyropheophorbide-a (Photochlor, HPPH) were amide-coupled to 1R,2S,3R,4R-2,3-dihydroxy-4-(hydromethyl)-1-aminocyclopentane and immobilized via an ester linkage to long chain alkyl amine-derivatized controlled pore glass (LCAA-CPG). The applicability of these supports (5 and 6) for the synthesis of porphyrin conjugates with oligomeric biomolecules was demonstrated using an automated phosphoramidite coupling chemistry. Cleavage from the support with concentrated ammonia gave the products, viz., porphyrin conjugates of oligonucleotides (7-9) and dendritic glycoclusters (10-13) and a cyclooctyne derivative (14) in 23-58% yield. In addition, the synthesized cyclooctyne derivative of meso-tris(pyridin-4-yl)(4-carboxyphenyl)porphyrin (14) was conjugated with an azidopropyl-modified hyaluronic acid (19). The hyaluronic acid-porphyrin conjugate (15) was radiolabeled with (64)Cu and its (15[(64)Cu]) receptor binding affinity to CD44-expressing tumor cells was evaluated.

The interaction of a β-fused isoindoline–porphyrin conjugate with nucleic acids

The intercalation of a diiminoisoindoline–porphyrin conjugate into the poly(dG–dC) double helix occurs by inducing the fast formation of the helix with temperature.

A toolset of functionalized porphyrins with different linker strategies for application in bioconjugation

Polar, functionalized A₃B-porphyrins are conjugated to hyperbranched polyglycerol (hPG) as an example of a biocompatible carrier system for photodynamic therapy.

Photodynamic Efficiency: From Molecular Photochemistry to Cell Death

Photodynamic therapy (PDT) is a clinical modality used to treat cancer and infectious diseases. The main agent is the photosensitizer (PS), which is excited by light and converted to a triplet excited state. This latter species leads to the formation of singlet oxygen and radicals that oxidize biomolecules. The main motivation for this review is to suggest alternatives for achieving high-efficiency PDT protocols, by taking advantage of knowledge on the chemical and biological processes taking place during and after photosensitization. We defend that in order to obtain specific mechanisms of cell death and maximize PDT efficiency, PSes should oxidize specific molecular targets. We consider the role of subcellular localization, how PS photochemistry and photophysics can change according to its nanoenvironment, and how can all these trigger specific cell death mechanisms. We propose that in order to develop PSes that will cause a breakthrough enhancement in the efficiency of PDT, researchers should first consider tissue and intracellular localization, instead of trying to maximize singlet oxygen quantum yields in in vitro tests. In addition to this, we also indicate many open questions and challenges remaining in this field, hoping to encourage future research.