Core-modified porphyrins. Part 4: Steric effects on photophysical and biological properties in vitro

Folate receptor-mediated enhanced and specific delivery of far-red light-activatable prodrugs of combretastatin A-4 to FR-positive tumor

We examined the concept of a novel prodrug strategy in which anticancer drug can be locally released by visible/near IR light, taking advantage of the photodynamic process and photo-unclick chemistry. Our most recently formulated prodrug of combretastatin A-4, Pc-(L-CA4)₂, showed multifunctionality for fluorescence imaging, light-activated drug release, and the combined effects of PDT and local chemotherapy. In this formulation, L is a singlet oxygen cleavable linker. Here, we advanced this multifunctional prodrug by adding a tumor-targeting group, folic acid (FA). We designed and prepared four FA-conjugated prodrugs 1–4 (CA4-L-Pc-PEG_n-FA: n = 0, 2, 18, ∼45) and one non-FA-conjugated prodrug 5 (CA4-L-Pc-PEG₁₈-boc). Prodrugs 3 and 4 had a longer PEG spacer and showed higher hydrophilicity, enhanced uptake to colon 26 cells via FR-mediated mechanisms, and more specific localization to SC colon 26 tumors in Balb/c mice than prodrugs 1 and 2. Prodrug 4 also showed higher and more specific uptake to tumors, resulting in selective tumor damage and more effective antitumor efficacy than non-FA-conjugated prodrug 5. FR-mediated targeting seemed to be an effective strategy to spare normal tissues surrounding tumors in the illuminated area during treatment with this prodrug.

MS/MS fragmentation behavior study of meso-phenylporphyrinoids containing nonpyrrolic heterocycles and meso-thienyl-substituted porphyrins

Free base and cobalt(II) complexes of six meso-tetraphenylporphyrinoids containing nonpyrrolic heterocycles and of three meso-thienylporphyrins were investigated using electrospray ionization tandem mass spectrometry (ESI-MS/MS). Their fragmentation was studied in a quadrupole ion trap as a function of the porphyrinoid macrocycle structure and compared with the fragmentation behavior of the benchmark compound meso-tetraphenylporphyrin. In situ oxidation of the neutral cobalt(II) complexes under ESI conditions produced singly charged cobalt(III) porphyrinoid ions; the free bases were ionized by protonation. For the porphyrinoids with an intact porphyrin core, the major fragmentation pathways observed were the losses of the meso-substituent (for meso-phenyl groups) and characteristic fragmentations of one or more meso-substituents (for the meso-thienyl group). Complex fragmentation pathways were observed for porphyrinoids with modifications to the porphyrin core but chemically reasonable structures could be assigned to most fragments, thus delineating general patterns for the behavior of pyrrole-modified porphyrins under CID conditions. ᅟ

Synthesis of carboxylate functionalized A3B and A2B2 thiaporphyrins and their application in dye-sensitized solar cells

Thiaporphyrins were effectively applied in dye-sensitized solar cells. Among them, N3S-ECN with an ethynylphenyl linker and cyanoacrylic acid anchor, achieved the highest efficiency of 1.69%.

A spectroscopic and theoretical investigation of a free-base meso-trithienylcorrole

The unique optical properties of free-base meso-tris(5-methylthien-2-yl)corrole were compared to those of the widely investigated meso-triphenyl-substituted analogue. A combination of spectroscopic and computational experiments was undertaken to elucidate the relationship between structural features of the neutral, mono-anionic and mono-cationic forms of the corroles and their corresponding optical properties. A general bathochromic shift was measured for the thienyl-substituted corrole. The experimental spectra are supported by excited state calculations. A systematic series of ground state minimizations were performed to determine energy minima for the flexible and solvent-sensitive molecules. Trithienylcorrole was found to have a more nonplanar macrocycle in conjunction with a high degree of π-overlap with the meso-substituents. Both structural features contribute to their bathochromically shifted optical spectra. The configurational character of the thienyl-substituted corrole is shown to have a larger degree of molecular orbital mixing and doubly excited character, which suggest a more complex electronic structure that does not fully adhere to the Gouterman four-orbital model. The reactivity of the thienyl groups, particularly with respect to their ability to be (electro)-polymerized, combined with the tight coupling of the meso-thienyl groups with the corrole chromophore elucidated in this work, recommends the meso-thienylcorroles as building blocks in, for instance, organic semiconductor devices.

Synthesis and in vitro biological evaluation of lipophilic cation conjugated photosensitizers for targeting mitochondria

Mitochondria-specific photosensitizers were designed by taking advantage of the preferential localization of delocalized lipophilic cations (DLCs) in mitochondria. Three DLC-porphyrin conjugates: CMP-Rh (a core modified porphyrin-rhodamine B cation), CMP-tPP (a core modified porphyrin-mono-triphenyl phosphonium cation), CMP-(tPP)(2) (a core modified porphyrin-di-tPP cation) were prepared. The conjugates were synthesized by conjugating a monohydroxy core modified porphyrin (CMP-OH) to rhodamine B (Rh B), or either one or two tPPs, respectively, via a saturated hydrocarbon linker. Their ability for delivering photosensitizers to mitochondria was evaluated using dual staining fluorescence microscopy. In addition, to evaluate the efficiency of the conjugates as photosensitizers, their photophysical properties and in vitro biological activities were studied in comparison to those of CMP-OH. Fluorescence imaging study suggested that CMP-Rh specifically localized in mitochondria. On the other hand, CMP-tPP and CMP-(tPP)(2) showed less significant mitochondrial localization. All conjugates were capable of generating singlet oxygen at rates comparable to CMP-OH. Interestingly, all cationic conjugates showed dramatic increase in cellular uptake and phototoxicity compared to CMP-OH. This improved photodynamic activity might be primarily due to an enhanced cellular uptake. Our study suggests that Rh B cationic group is better at least for CMP than tPP as a mitochondrial targeting vector.

Structural effects of core-modified porphyrins in dye-sensitized solar cells

A series of core-modified porphyrins with different meso aryl groups ( R 1), anchoring groups ( R 2), and core atoms (X) were studied as light-harvesting sensitizers for dye-sensitized solar cells (DSSCs). DSSCs were fabricated using these porphyrins as well as TiO2 nanoparticles with a particle diameter of around 25 nm. A dense layer of TiO2 was deposited as an interfacial layer on fluorine-doped tin dioxide (FTO) substrates. A TiO2 nanocrystalline film was then deposited on the dense layer by spin coating. The comparison of DSSC performance from different core-modified porphyrins was studied. The UV-vis absorption spectroscopy of porphyrin films attached on TiO2 and porphyrin solutions were also measured. The results indicated that both anchoring and meso aryl groups impacted on cell performance. The cell efficiency was correlated to the absorption of porphyrin films attached on TiO2 at the Soret band.

Synthesis, spectral data, and crystal structure of two novel substitution patterns in dithiaporphyrins

The syntheses, characterizations and crystal structures of 5-(4-tert-butylphenyl)-15,20-diphenyl-10-(4-methoxy)phenyl-21,23-dithiaporphyrin (1b) and 2,3-dimethoxy-10,15-diphenyl-21,23-dithiaporphyrin (2) are described. The cyclization of 2-[1-(4-methoxyphenyl)-1-pyrrolomethyl]-5-(1-phenyl-1-pyrrolomethyl)thiophene and 2-[1-(4-t-butylphenyl)-1-hydroxymethyl]-5-(1-phenyl-1-hydroxymethyl)thiophene gave predominantly the cis-regioisomer, which was characterized by X-ray crystallography.

Origin of the bathochromically shifted optical spectra of meso-tetrathien-2′- and 3′-ylporphyrins as compared to meso-tetraphenylporphyrin

The UV-Vis and fluorescence spectra of free base and diprotonated meso-tetrathien-2'-ylporphyrins are, when compared to the spectra of meso-tetra-phenyl- or even -thien-3'-ylporphyrins, characterized by surprisingly large red-shifts. A comparison of the optical spectra and the computed rotational barriers for these meso-aryl-substituted porphyrins and a detailed conformational analysis of the single crystal X-ray structure of a diprotonated meso-tetrathien-2'-ylporphyrin suggest that the origin of the altered electronic properties of meso-tetrathien-2'-ylporphyrins are mainly due to the contribution of conformations in which the thienyl groups adopt idealized co-planar arrangements with the porphyrin ring. These conformations allow an efficient extension of the porphyrinic pi-system through conjugation. We synthesized a meso-tetrathien-2'-ylporphyrin with methyl groups in the o-position, thus preventing the formation of conformers with co-planar thienyl groups and a corresponding thien-2'-ylporphyrin with methyl substituents in a distal position that possesses the same steric requirements for thienyl group rotation as the parent compound, to conclusively deduce the influence of the conformers on the electronic structure. A MNDO-PSDCI computation of their optical spectra further supports our key hypothesis. DFT computations of the total energies of the hypothetical diprotonated thien-2'-ylporphyrin conformer with perpendicular thienyl groups and the conformer containing near-co-planar thienyl groups quantify the resonance stabilization energy. Our results support and complement recent photophysical and theoretical studies by Gupta and Ravikanth and Friedlein et al. on thien-2'-yl-substituted core-modified porphyrins and [meso-tetra(5'-bromothien-2'-yl)porphyrinato]Zn(ii), respectively.

Core-modified porphyrins. Part 5: Electronic effects on photophysical and biological properties in vitro

21,23-Dithiaporphyrins 2-11 were prepared as analogues of 5,20-diphenyl-10,15-bis(4-carboxylatomethoxy)phenyl-21,23-dithiaporphyrin 1 to examine the impact of electronic properties at the 5- and 20-meso-positions. The effects of the electronic properties at the meso-rings were not significant with respect to absorption spectra, quantum yields for the generation of singlet oxygen and for fluorescence. While some differences were noted in the n-octanol/pH 7.4 buffer partition coefficient, log D(7.4), among the compounds, log D(7.4) did not critically influence the cellular uptake or phototoxicity. None of the dithiaporphyrins 1-11 displayed dark toxicity at concentrations up to 1 x 10(-5) M. Once irradiated with 5 J cm(-2) of 350-750 nm light, five porphyrins 2, 3, 5, 6, and 8 killed over 80% of R3230AC rat mammary adenocarcinoma cells at 5 x 10(-7) M photosensitizer. Among these five, compound 3 bearing 5-phenyl and 20-(4-fluorophenyl) substituents was the most potent photosensitizer toward R3230AC cells showing 67% cell kill at 1 x 10(-7) M 3. Bulky substituents at the 5- and 20-positions gave photosensitizers with minimal phototoxicity.