Small Alterations in Cobinamide Structure Considerably Influence sGC Activation

Specially designed B‐ring‐modified cobalamin derivatives were synthesized and tested as potential activators of soluble guanylyl cyclase (sGC). Herein, we disclose the influence of substituents at the c‐ and d‐positions in hydrophilic and hydrophobic cobyrinic acid derivatives on their capacities to activate sGC. The presence of the amide group at c‐/d‐position in cobyrinic acid derivatives strongly influence the level of sGC activation. Removal of the d‐position altogether has a profound effect for hydrophobic compounds. In contrast, little differences were observed in hydrophilic ones.     

Synthesis of Functionalized trans‐A2B2‐Porphyrins Using Donor–Acceptor Cyclopropane‐Derived Dipyrromethanes

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.     

Novel meso-substituted porphyrins: Synthesis, characterization and photocatalytic activity of their TiO2-based composites

Two series of novel meso-substituted porphyrins, namely 5,10,15,20-tetra[4-(3-phenoxy)-propoxy]phenyl porphyrin, the structural analogue 5,10,15,20-tetra[2-(3-phenoxy)-propoxy]phenyl porphyrin and their Co(II) Cu(II) and Zn(II) complexes were synthesized. The compounds were characterized using various spectroscopic techniques and their molecular structure was proposed based on density functional theory calculations. The diverse properties of the porphyrin derivatives result from the different stereochemistry of the particular substituents at the meso site on the macrocycle and are controlled also by the coordinated metal. The ¹H NMR spectrum of the free-base porphyrin showed a complicated spin-splitting. The photocatalytic activities in degradation of 4-nitrophenol were investigated using polycrystalline TiO₂ impregnated with the porphyrins and metalloporphyrins. The Cu(II) porphyrin was a more effective sensitizer than other metal containing compounds (M = Co, Zn) as well as the free-base. Photocatalytic activity was also influenced by spatial positions of the substitutions on the porphyrin molecules.     

The synthesis and photodynamic properties of meso-substituted, cationic porphyrin derivatives in HeLa cells

A series of asymmetric porphyrins with varying substituents, such as 4-hydrophenyl and N-methyl-4-pyridyl, were synthesized and characterized and their cell uptake, intracellular localization, cytotoxicities and phototoxicities were evaluated in vitro. The most phototoxic of the porphyrins synthesized, 5,10-di-(N-methyl-4-pyridyl)-15,20-(4-hydroxyphenyl)-21,23H-porphyrin, which was mainly localized in the mitochondria and displayed low levels of dark toxicity toward human cancer HeLa cells, offers potential application in photodynamic therapy.     

Templated self-assembly of porphyrin cages

The development of self-assembling catalysts, although an often-tried approach, has achieved little success so far. Toward the construction of substrate selective catalysts, we have self-assembled a porphyrin cage based upon the recognition of the templates meso-dipyridyl ( DPyP ) or meso-tetrapyridyl porphyrin ( TPyP ) by glycoluril-based receptors that are functionalized with two pendant zinc porphyrins.     

Distinct Pharmacological Properties of Gaseous CO and CO-Releasing Molecule in Human Platelets

Carbon monoxide (CO)—gaseous or released by CO-RMs—both possess antiplatelet properties; however, it remains uncertain whether the mechanisms involved are the same. Here, we characterise the involvement of soluble guanylate cyclase (sGC) in the effects of CO—delivered by gaseous CO–saturated buffer (CO_G) and generated by CORM-A1—on platelet aggregation and energy metabolism, as well as on vasodilatation in aorta, using light transmission aggregometry, Seahorse XFe technique, and wire myography, respectively. ODQ completely prevented the inhibitory effect of CO_G on platelet aggregation, but did not modify antiplatelet effect of CORM-A1. In turn, CO_G did not affect, whereas CORM-A1 substantially inhibited energy metabolism in platelets. Even though activation of sGC by BAY 41-2272 or BAY 58-2667 inhibited significantly platelet aggregation, their effects on energy metabolism in platelets were absent or weak and could not contribute to antiplatelet effects of sGC activation. In contrast, vasodilatation of murine aortic rings, induced either by CO_G or CORM-A1, was dependent on sGC. We conclude that the source (CO_G vs. CORM-A1) and kinetics (rapid vs. slow) of CO delivery represent key determinants of the mechanism of antiplatelet action of CO, involving either impairment of energy metabolism or activation of sGG.     

Insight into the rescue of oxidized soluble guanylate cyclase by the activator cinaciguat

Nitric oxide (NO) signaling mediates many important physiological processes through the receptor soluble guanylate cyclase (sGC). Under disease conditions sGC heme can be oxidized resulting in NO insensitivity. Here, we show that the therapeutic compound cinaciguat (Cin) rescues dysfunctional sGC by direct displacement of the oxidized heme.     

Structural Perspectives on the Mechanism of Soluble Guanylate Cyclase Activation

The enzyme soluble guanylate cyclase (sGC) is the prototypical nitric oxide (NO) receptor in humans and other higher eukaryotes and is responsible for transducing the initial NO signal to the secondary messenger cyclic guanosine monophosphate (cGMP). Generation of cGMP in turn leads to diverse physiological effects in the cardiopulmonary, vascular, and neurological systems. Given these important downstream effects, sGC has been biochemically characterized in great detail in the four decades since its discovery. Structures of full-length sGC, however, have proven elusive until very recently. In 2019, advances in single particle cryo–electron microscopy (cryo-EM) enabled visualization of full-length sGC for the first time. This review will summarize insights revealed by the structures of sGC in the unactivated and activated states and discuss their implications in the mechanism of sGC activation.     

Repurposing Riociguat to Target a Novel Paracrine Nitric Oxide-TRPC6 Pathway to Prevent Podocyte Injury

Increased expression and activity of the Ca²⁺ channel transient receptor potential channel 6 (TRPC6) is associated with focal segmental glomerulosclerosis, but therapeutic strategies to target TRPC6 are currently lacking. Nitric oxide (NO) is crucial for normal glomerular function and plays a protective role in preventing glomerular diseases. We investigated if NO prevents podocyte injury by inhibiting injurious TRPC6-mediated signaling in a soluble guanylate cyclase (sGC)-dependent manner and studied the therapeutic potential of the sGC stimulator Riociguat. Experiments were performed using human glomerular endothelial cells and podocytes. Podocyte injury was induced by Adriamycin incubation for 24 h, with or without the NO-donor S-Nitroso-N-acetyl-DL-penicillamine (SNAP), the sGC stimulator Riociguat or the TRPC6 inhibitor Larixyl Acetate (LA). NO and Riociguat stimulated cGMP synthesis in podocytes, decreased Adriamycin-induced TRPC6 expression, inhibited the Adriamycin-induced TRPC6-mediated Ca²⁺ influx and reduced podocyte injury. The protective effects of Riociguat and NO were blocked when sGC activity was inhibited with 1H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) or when TRPC6 activity was inhibited by LA. Our data demonstrate a glomerular (e)NOS-NO-sGC-cGMP-TRPC6 pathway that prevents podocyte injury, which can be translated to future clinical use by, e.g., repurposing the market-approved drug Riociguat.     

Evaluation of the Correlation between Porphyrin Accumulation in Cancer Cells and Functional Porphyrin Positions of the Phenyl Group

Porphyrin selectively shows tumour accumulation and has attracted attention as a carrier molecule for drug delivery systems (DDS). Porphyrin has two functional sites termed the meso- and β-positions. In previous work, meso-porphyrin derivatives with an alkyl group were found to exhibit greater accumulation in human breast cancer cells (MCF-7). To identify the correlation between porphyrin accumulation and functional porphyrin positions of other functional groups, the accumulation of porphyrin derivatives with a phenyl group was investigated. The β-porphyrin derivative with a phenyl group showed higher accumulation in MCF-7 cells and greater affinity for albumin than the meso-porphyrin derivative. The results of density functional theory (DFT) calculations suggest that the β-porphyrin derivative with a phenyl group had higher planarity across the total structure than the meso-porphyrin derivative. It was concluded that the greater planarity of the β-porphyrin derivative with a phenyl group might lead to superior MCF-7 cell accumulation.     

Hexaphyrin as a Potential Theranostic Dye for Photothermal Therapy and 19F Magnetic Resonance Imaging

Two features of meso‐Aryl‐substituted expanded porphyrins suggest suitability as theranostic agents. They have excellent absorption in near infrared (NIR) region, and they offer the possibility of introduction of multiple fluorine atoms at structurally equivalent positions. Here, hexaphyrin (hexa) was synthesized from 2,6‐bis(trifluoromethyl)‐4‐formyl benzoate and pyrrole and evaluated as a novel expanded porphyrin with the above features. Under NIR illumination hexa showed intense photothermal and weak photodynamic effects, which were most likely due to its low excited states, close to singlet oxygen. The sustained photothermal effect caused ablation of cancer cells more effectively than the photodynamic effect of indocyanine green (a clinical dye). In addition, hexa showed potential for use in the visualization of tumors by ¹⁹F magnetic resonance imaging (MRI), because of the multiple fluorine atoms. Our results strongly support the utility of expanded porphyrins as theranostic agents in both photothermal therapy and ¹⁹F MRI.     

Facial discrimination in monoarylporphyrins: Synthesis and stereochemical behaviour of bis(ligated) monospirobifluorenylporphyrin ruthenium complexes

Condensation of dipyrromethane, pyrrole-2-carbaldehyde with either 9,9′-spirobifluorene or fluorene aldehyde yields new meso-monosubstituted, β-unsubstituted porphyrins. The large size of spirobifluorene hinders the rotation around the C_meso–C_aryl bond to give, for bis-ligated complexes, two different topological faces.     

Cytotoxicities of Tumor-Seeking Dyes: Impact on Future Clinical Trials

Heptamethine (Cy7) dyes with meso-Cl substituents injected intravenously (iv) into mice accumulate in tumors and persist there over several days. We believe this occurs via meso-Cl displacement by the only free cysteine residues of albumin; therefore, conjugating tumor-seeking dyes with fragments can increase selective therapeutic delivery to tumors and drug residence. This strategy has elevated significance recently because the first tumor-seeking dye-drug conjugate has moved into clinical trials. Options for further clinical research include modifying the dye, and use of preformed albumin adducts instead of dyes alone. Herein we show correlations of cytotoxicities, lipophilicities, organelle localization, apoptosis, cell-cycle arrest, wound healing/migration assays, and reactivities/affinities with human serum albumin are difficult to observe. However, our studies arrived at an important conclusion: preformed dye-drug-HSA adducts are less cytotoxic, and therefore preferable for subsequent clinical work, relative to direct injection of meso-Cl-containing forms.     

Pb2+ as a Substrate and a Cofactor of a Porphyrin Metalation DNAzyme

We herein report a DNAzyme named T30695 (sequence: (G₃T)₄) that can catalyze Zn²⁺ insertion into three different porphyrins in the presence of Pb²⁺ as a cofactor. Meanwhile, T30695 with Pb²⁺ alone was found to cause a shift in both the fluorescence and UV-vis spectra of protoporphyrin IX (PPIX), thus suggesting that metalation of Pb²⁺ was also achieved at room temperature. From kinetic measurements, the reaction required two Pb²⁺ ions; this is consistent with one being a cofactor and the other being a substrate. No previous reports inserted Pb²⁺ into porphyrins by using DNAzymes or protein-based enzymes. This reaction was most significantly inhibited in the presence of K⁺ followed by Na⁺ and Li⁺, suggesting the importance of the Pb²⁺-stabilized G-quadruplex. When Pb²⁺ is inserted into PPIX, its emission blue shifts from 635 to 590 nm, thus allowing simple ratiometric fluorescent sensing with a detection limit of 1.2 nM Pb²⁺.     

Photochromic Diarylethene Derivatives Bearing Hydrophilic Substituents

Photochromic diarylethene derivatives bearing hydrophilic N,N-bis(2-(2-(2-methoxyethoxy)ethoxy)ethyl)sulfonamide (SO₂NTEG₂) ( 1 – 3 ) or myo-inositol ( 4 – 6 ) substituents were synthesized. Although the solubility in aqueous solution of the derivatives containing the four tri(ethylene glycol) chains was relatively poor, the solubility was improved by introducing two myo-inositol residues. The derivatives could be dissolved even in pure water and underwent photochromism upon alternate irradiation with ultraviolet (UV) and visible light, in both organic and aqueous solutions. The absorption maxima of the open- and closed-ring isomers of these derivatives and the photostationary conversion ratios from the open- to the closed-ring isomers upon UV irradiation did not change much, even when the solvent polarity was changed. These results indicate that the diarylethene derivatives are mono-molecularly dissolved in aqueous solution and that intermolecular interactions between the derivatives are negligible when the concentration is less than 1×10⁻⁴ mol⋅L⁻¹.     

Synthesis of 1,3,5,5-tetranitrohexahydropyrimidine

1,3,5,5-Tetranitrohexahydropyrimidine, (1), was synthesized by the oxidative nitrolysis of 1,3-diisopropyl-5,5-dinitrohexahydropyrimidine, (2), with 90% nitric acid. The course of the reaction was influenced by both the n-alkyl substituents and the nitrolyzing medium. Compound 1 was synthesized by nitrolysis of N,N-diisopropyl or dicyclohexyl substituents, while dimethyl, diethyl, or other di-n-alkyl substituents yielded ring-cleaved products 3 and/or 4. Similar effects were observed by varying the nitric acid concentration. The formation of nitramine products, rather than nitrosamine or alkyl amide products that generally result from tertiary amine nitrolysis, is attributed to conformational changes in a postulated nitronium ion-amine complex intermediate.     

The synthesis of novel photochromic diarylethenes bearing a biphenyl moiety and the effects of substitution on their properties

A new class of diarylethene bearing a biphenyl moiety was synthesized and the effects of substitution on photochromism, fluorescence and electrochemical character, were investigated. Under alternating irradiation with UV and visible light, the compounds exhibited good photochromism and functioned as fluorescent photoswitches both in solution and in PMMA film. Electron-donating substituents shifted the λ_max of the diarylethenes to longer wavelengths and decreased their cyclization quantum yield, while electron-withdrawing substituents greatly increased both cyclization and cycloreversion quantum yield. In addition, cyclic voltammetry revealed that the substituents had a significant effect on the electrochemical behaviour of the diarylethene derivatives.     

Cation Radicals of Covalently Linked Porphyrin Dimers and their Monomeric Constituents: An ESR and ENDOR Study

The spin density distributions in the cation radicals of various covalently linked porphyrin dimers have been studied by liquid phase ESR and ENDOR methods to find out whether these systems show intramolecular electron delocalization. Such a delocalization is known to occur in the bacteriochlorophyll dimer (“special pair”) in the photosynthetic reaction center. The dimers that were studied in this work were derived from zinc mesotetratolylporphyrin (ZnTTP) and linked at the ortho or para positions of one phenyl ring with varying bridge lengths. ¹H and ^I4N hyperfine coupling constants could be measured for the dimer cation radicals and compared with those of monomeric ZnTTP as well as ZnTTP derivatives that carry alkoxy or hydroxy substituents to mimic the bridges of the dimers. By comparing the hyperfine data of the monomer and dimer cation radicals it is concluded that in the present dimers the unpaired electron is localized on one porphyrin unit.     

The Effect of Alkyl Substituents on Actinide and Lanthanide Extraction by Diglycolamide Compounds

The effect of the alkyl substituents on amidic N atoms in diglycolamide (DGA) compounds on solvent extraction has been investigated. The solubility in water and n-dodecane, lanthanide loading capacity, and distribution ratios (D) of lanthanides and actinides for various DGA compounds are reported. DGA derivatives with short alkyl chains, for example, methyl and ethyl groups, are very water soluble, while DGA derivatives with long alkyl chains, for example, octyl (TODGA), decyl (TDDGA), dodecyl (TDdDGA), and 2-ethylhexyl (TEHDGA) group are moderately soluble in n-dodecane. DGA derivatives with phenyl substituents have very low solubility in both aqueous and organic solvents, which suggests that these compounds will not be suitable for solvent extraction applications in the HNO₃/n-dodecane systems. The lanthanide loading capacities of DGA extractants correlate with their alkyl chain lengths according to the following order: TDdDGA > TDDGA > TODGA > TEHDGA. The branched-alkyl-chain DGA derivative (TEHDGA) exhibits both lower D and loading capacity than TODGA. The results of masking-effect and solubility tests indicate that TEDGA is the best actinide masking agent among the water-soluble DGA derivatives tested. Actinide and lanthanide extractions using ten DGA compounds in six diluents (nitrobenzene, 1,2-dichloroethane, 1-octanol, chloroform, toluene, and n-dodecane) are also reported; it was observed that lipophilic DGA derivatives with shorter alkyl chains show higher D values.