Functionalized heterocycle-appended porphyrins: catalysis matters

Peripheral Groups of Dicationic Pyrazinoporphyrins Regulate Lipid Membrane Binding

Photodynamic therapy (PDT) is a widely used technique for skin cancer treatment and antimicrobial therapy. An improvement in PDT efficiency requires not only an increase in quantum yield of photosensitizer (PS) molecules but also their applicability for biological systems. Recently, we demonstrated that the activity of porphyrin-based PSs in the lipid membrane environment depends on the nature of the cation in the macrocycle due to its interactions with the lipid phosphate moiety, as well as the orientation of the PS molecules inside the membrane. Here, we report the synthesis, membrane binding properties and photodynamic efficiency of novel dicationic free-base, Ni(II) and Zn(II) pyrazinoporphyrins with terminal tetraalkylammonium units (2H-1, Ni-1 and Zn-1), to show the possibility to enhance the membrane binding of PS molecules, regardless of the central cation. All of these substances adsorb at the lipid membrane, while free-base and Zn(II) porphyrins actively generate singlet oxygen (SO) in the membranes. Thus, this study reveals a new way to tune the PDT activity of PSs in biological membranes through designing the structure of the peripheral groups in the macrocyclic photosensitizer.

Functionalized heterocycle-appended porphyrins: catalysis matters

The scope and limitations of the condensation of labile 2,3-diaminoporphyrin derivatives with aromatic aldehydes to provide functionalized imidazole- and pyrazine-appended porphyrins were investigated in detail. The presence of an acidic catalyst in the reaction was found to be a tool that allows the reaction path to be switched. The influence of the electronic origin of the substituents in the carbonyl components of the condensation on the yields and selectivity of the reaction was revealed. Metal-promoted cross-coupling transformations were found to be convenient for the further targeted construction of functional derivatives based on the prepared bromo-substituted pyrazinoporphyrins. Overall, these strategies provide a versatile technique for the elaboration of a variety of functionalized heterocycle-appended porphyrins for further application in the development of hybrid materials.

The condensation of labile 2,3-diaminoporphyrins with aromatic aldehydes is a versatile technique for the elaboration of functionalized porphyrins. The acidic catalyst in the reaction is a tool that allows the reaction path to be switched.