Synthesis, photophysical properties, tumor uptake, and preliminary in vivo photosensitizing efficacy of a homologous series of 3-(1'-alkyloxy)ethyl-3-devinylpurpurin-18-N-alkylimides with variable lipophilicity

Photodynamic Inactivation of Microorganisms Using Semisynthetic Chlorophyll a Derivatives as Photosensitizers

In this study, we describe the semisynthesis of cost-effective photosensitizers (PSs) derived from chlorophyll a containing different substituents and using previously described methods from the literature. We compared their structures when used in photodynamic inactivation (PDI) against Staphylococcus aureus, Escherichia coli, and Candida albicans under different conditions. The PSs containing carboxylic acids and butyl groups were highly effective against S. aureus and C. albicans following our PDI protocol. Overall, our results indicate that these nature-inspired PSs are a promising alternative to selectively inactivate microorganisms using PDI.

Chiral Alkyl Groups at Position 3(1') of Pyropheophorbide-a Specify Uptake and Retention by Tumor Cells and Are Essential for Effective Photodynamic Therapy

To investigate the importance of the chirality and precise structure at position 3(1') of pyropheophorbide-a for tumor cell specificity and photodynamic therapy (PDT), a series of photosensitizers (PSs) was synthesized: (a) with and without chirality at position 3(1'), (b) alkyl ether chain with a variable number of chiral centers, (c) hexyl ether versus thioether side chain, and (d) methyl ester versus carboxylic acid group at position 17². The cellular uptake and specificity were defined in human lung and head/neck cancer cells. PSs without a chiral center and with an alkyl chain or thioether functionalities showed limited uptake and PDT efficacy. Replacing the methyl group at the chiral center with a propyl group or introducing an additional chiral center improved cellular retention and tumor cell specificity. Replacing the carboxylic acid with methyl ester at position 17² lowered cellular uptake and PDT efficacy. A direct correlation between the PS uptake in vitro and in vivo was identified.

Autophagy Regulation and Photodynamic Therapy: Insights to Improve Outcomes of Cancer Treatment

Cancer is considered an age-related disease that, over the next 10 years, will become the most prevalent health problem worldwide. Although cancer therapy has remarkably improved in the last few decades, novel treatment concepts are needed to defeat this disease. Photodynamic Therapy (PDT) signalize a pathway to treat and manage several types of cancer. Over the past three decades, new light sources and photosensitizers (PS) have been developed to be applied in PDT. Nevertheless, there is a lack of knowledge to explain the main biochemical routes needed to trigger regulated cell death mechanisms, affecting, considerably, the scope of the PDT. Although autophagy modulation is being raised as an interesting strategy to be used in cancer therapy, the main aspects referring to the autophagy role over cell succumbing PDT-photoinduced damage remain elusive. Several reports emphasize cytoprotective autophagy, as an ultimate attempt of cells to cope with the photo-induced stress and to survive. Moreover, other underlying molecular mechanisms that evoke PDT-resistance of tumor cells were considered. We reviewed the paradigm about the PDT-regulated cell death mechanisms that involve autophagic impairment or boosted activation. To comprise the autophagy-targeted PDT-protocols to treat cancer, it was underlined those that alleviate or intensify PDT-resistance of tumor cells. Thereby, this review provides insights into the mechanisms by which PDT can be used to modulate autophagy and emphasizes how this field represents a promising therapeutic strategy for cancer treatment.

Enhanced Cellular Uptake and Photodynamic Effect with Amphiphilic Fluorinated Porphyrins: The Role of Sulfoester Groups and the Nature of Reactive Oxygen Species

A class of amphiphilic photosensitizers for photodynamic therapy (PDT) was developed. Sulfonate esters of modified porphyrins bearing-F substituents in the ortho positions of the phenyl rings have adequate properties for PDT, including absorption in the red, increased cellular uptake, favorable intracellular localization, low cytotoxicity, and high phototoxicity against A549 (human lung adenocarcinoma) and CT26 (murine colon carcinoma) cells. Moreover, the role of type I and type II photochemical processes was assessed by fluorescent probes specific for various reactive oxygen species (ROS). The photodynamic effect is improved not only by enhanced cellular uptake but also by the high generation of both singlet oxygen and oxygen-centered radicals. All of the presented results support the idea that the rational design of photosensitizers for PDT can be further improved by better understanding the determinants affecting its therapeutic efficiency and explain how smart structural modifications can make them suitable photosensitizers for application in PDT.

Synthesis and Self-Assembly Behavior of Chlorophyll Derivatives for Ratiometric Photoacoustic Signal Optimization

Self-assembly provides researchers powerful tools for creating ordered functional structures and complex architectures. Investigation of in vivo self-assembly reveals the assembly/aggregation-induced retention (AIR) effect and enhanced targeting effect, which can be applied to promising biomedical applications by enhancing molecular accumulation in the target region. These unique bioeffects inspire the interest of researchers in construction of self-assembled nanomaterials in biological systems. Although many efforts have been achieved, the in-depth analysis of the relationship between assemblies and functions is rarely reported. Here, we focus on the relationship of chlorophyll-derivative assemblies and their photoacoustic signals and attempt to establish a method for monitoring the aggregation efficiency in vivo based on photoacoustic signals. Three arginine-rich peptide-purpurin molecules were designed and synthesized. The assembled capabilities and assembly processes of these molecules were characterized and monitored by UV, fluorescence, and CD spectra images of gradually changing polarities in mixed solvents, and the morphologies of the assemblies were observed by TEM. Furthermore, the relationship between the aggregation ratios of the molecules and the ratiometric photoacoustic signals was systemically studied. We prospect that the fundamental research in revealing objective laws will be useful for future guidance in optimizing photoacoustic detection windows and assembled molecule design.

Synthesis and evolution of S-Porphin sodium as a potential antitumor agent for photodynamic therapy against breast cancer

The novel sensitizer S-Porphin sodium can generate ROS by radiation with a long wavelength to cause tumor cell death.

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

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

Oncologic Photodynamic Therapy: Basic Principles, Current Clinical Status and Future Directions

Photodynamic therapy (PDT) is a clinically approved cancer therapy, based on a photochemical reaction between a light activatable molecule or photosensitizer, light, and molecular oxygen. When these three harmless components are present together, reactive oxygen species are formed. These can directly damage cells and/or vasculature, and induce inflammatory and immune responses. PDT is a two-stage procedure, which starts with photosensitizer administration followed by a locally directed light exposure, with the aim of confined tumor destruction. Since its regulatory approval, over 30 years ago, PDT has been the subject of numerous studies and has proven to be an effective form of cancer therapy. This review provides an overview of the clinical trials conducted over the last 10 years, illustrating how PDT is applied in the clinic today. Furthermore, examples from ongoing clinical trials and the most recent preclinical studies are presented, to show the directions, in which PDT is headed, in the near and distant future. Despite the clinical success reported, PDT is still currently underutilized in the clinic. We also discuss the factors that hamper the exploration of this effective therapy and what should be changed to render it a more effective and more widely available option for patients.

Synthesis and in vitro phototoxicity of novel π-extension derivatives of chlorin e6

3²-Aryl substitution generated the maximum wavelength redshift and increased the in vitro phototoxicity against HepG2 cells simultaneously.

Highly Effective Dual-Function Near-Infrared (NIR) Photosensitizer for Fluorescence Imaging and Photodynamic Therapy (PDT) of Cancer

We report herein the synthesis and biological efficacy of near-infrared (NIR), bacteriochlorin analogues: 3-(1'-butyloxy)ethyl-3-deacetyl-bacteriopurpurin-18-N-butylimide methyl ester (3) and the corresponding carboxylic acid 10. In in vitro assays, compared to its methyl ester analogue 3, the corresponding carboxylic acid derivative 10 showed higher photosensitizing efficacy. However, due to drastically different pharmacokinetics in vivo, the PS 3 (HPLC purity >99%) showed higher tumor uptake and long-term tumor cure than 10 (HPLC purity >96.5%) in BALB/c mice bearing Colon 26 tumors. Isomerically pure R- and S- isomers of 3 (3a and 3b, purity by HPLC > 99%) under similar treatment parameters showed identical efficacy in vitro and in vivo. In addition, photosensitizer (PS) 3 showed limited skin phototoxicity and provides an additional advantage over the clinically approved chemically complex hematoporphyrin derivative as well as other porphyrin-based PDT agents, which makes 3 a promising dual-function agent for fluorescence-guided surgery with an option of phototherapy of cancer.

Photodynamic efficiency of a chlorophyll-a derivative in vitro and in vivo

This paper reports the antitumor activity of a chlorophyll-a derivative, 2-[1-hydroxyethyl]-2-devinylpyropheophorbide-a (HEPa). Photophysical characteristics of HEPa were measured. And its cytotoxicity, intracellular localization, biodistribution, efficiency of photodynamic therapy (PDT), histological analysis were investigated using human bile duct carcinoma cells (QBC-939) and QBC-939 tumor bearing BABL/c nude mice as animal model. The results showed that HEPa was localized mainly within the cytoplasmic region and partially in lysosome. Biodistribution of HEPa in QBC-939 tumor bearing BABL/c nude mice showed its fast rate of clearance and high tumor selectivity. In vitro, HEPa had low dark toxicity and high photoxicity against QBC-939 cells. The inhibition rate of QBC-939 tumor could increase up to 92.3%, and H&E staining confirmed that HEPa could cause serious damage to the tumor with light dose of 100J/cm(2), implying that HEPa has potential to be a new antitumor candidate for photodynamic therapy (PDT).

Synthesis of amide derivatives of chlorin e6 and investigation of their biological activity

In this work there is a synthesis of new photosensitizers which is based on amide derivatives of chlorin е6 . For the disclosure of an extra ring of the initial compound - pheophorbide a 1, we used primary aliphatic amines with 4-12 carbon atoms in the alkyl chain. The reaction is carried out under mild conditions in chloroform with heating to 40 ºС. The structure of all compounds obtained was confirmed by means of electronic, IR, 1Н-NMR spectroscopy and mass-spectrometry. The photoactivity and the dark toxicity of the compounds 2b-2h were investigated on two cancer cell lines: P-388 and K-562. The biological investigations revealed a good photoactivity and low dark toxicity of all compounds 2b-2f. The amide derivatives of chlorin е6 with 6 and 7 carbon atoms in the alkyl part showed the best results in our research. Thus, in this paper we propose a reliable scheme of synthesis of chlorin's photosensitizers which are promising agents for PDT.

Effect of chirality on cellular uptake, imaging and photodynamic therapy of photosensitizers derived from chlorophyll-a

We have previously shown that the (124)I-analog of methyl 3-(1'-m-iodobenzyloxy) ethyl-3-devinyl-pyropheophorbide-a derived as racemic mixture from chlorophyll-a can be used for PET (positron emission tomography)-imaging in animal tumor models. On the other hand, as a non-radioactive analog, it showed excellent fluorescence and photodynamic therapy (PDT) efficacy. Thus, a single agent in a mixture of radioactive ((124)I-) and non-radioactive ((127)I) material can be used for both dual-imaging and PDT of cancer. Before advancing to Phase I human clinical trials, we evaluated the activity of the individual isomers as well as the impact of a chiral center at position-3(1) in directing in vitro/in vivo cellular uptake, intracellular localization, epithelial tumor cell-specific retention, fluorescence/PET imaging, and photosensitizing ability. The results indicate that both isomers (racemates), either as methyl ester or carboxylic acid, were equally effective. However, the methyl ester analogs, due to subcellular deposition into vesicular structures, were preferentially retained. All derivatives containing carboxylic acid at the position-17(2) were noted to be substrate for the ABCG2 (a member of the ATP binding cassette transporters) protein explaining their low retention in lung tumor cells expressing this transporter. The compounds in which the chirality at position-3 has been substituted by a non-chiral functionality showed reduced cellular uptake, retention and lower PDT efficacy in mice bearing murine Colon26 tumors.

Synthesis, optical properties and preliminary in vitro photodynamic effect of pyridyl and quinoxalyl substituted chlorins

A series of chlorophyll a-based chlorins conjugated with pyridyl or quinoxalyl group at different positions were synthesized, characterized and evaluated for their photodynamic effect in vitro. It was found that all the pyridyl and quinoxalyl chlorins showed promising photocytotoxicities but nontoxic without irradiation in HeLa cells, and the substituted types and positions had a significant influence on the photocytotoxicities of the chlorophyll a-based chlorins. All the chlorins with a pyridyl group at the C-D ring end exhibited relatively high photocytotoxicity as compared to those with 3(2)-pyridyl. Among them, compound 12 conjugated with a pyridyl group at its C12 position showed the best photodynamic effect in HeLa cells with an IC50 value of 0.033μM. These facts, associated with the relative high long wavelength absorptions of those chlorins may provide valuable ways to design and prepare promising photosensitizers for application in photodynamic therapy.

Highly efficient synthesis of novel methyl 132-methylene mesopyropheophorbide a and its stereoselective Michael addition reaction

pH-Dependent regioselective condensation of methyl mesopyropheophorbide a with HCHO is studied and stereoselective Michael reaction of the 13²-methylene product is also discussed.

Synthesis and characterization of novel purpurinimides as photosensitizers for photodynamic therapy

A series of novel purpurinimides with long wavelength absorption were designed and synthesized to develop novel and potential photosensitizers. These compounds were investigated through reduction, oxidation, rearrangement reaction and amidation reactions of methyl pheophorbide a. They demonstrated a considerable bathochromic shift of the major absorption band in the red region of the optical spectrum (695–704 nm). Newly synthesized purpurinimides were screened for their antitumor activities, and showed higher photodynamic efficiency against A549 cell lines as compared to purpurin-18 methyl ester. The results revealed the novel purpurinimides could be potential photosensitizers.

Phototoxic effects of pyropheophorbide-a from chlorophyll-a on cervical cancer cells

Photodynamic therapy (PDT) is a promising modality in both the curative and palliative treatment against a variety of experimental and naturally occurring human cancers. At present, chlorophyll a derivatives are extensively used for the synthesis of photosensitizers (PSs) for PDT of tumors. In the present study, chlorophyll-a was extracted from the blue-green algae Spirulina platensis by refluxing with acetone. The extract was further acid treated to obtain methylpheophorbide-a (MPa), which was then refluxed in collidine and methylpyropheophorbide-a (Mppa) was obtained. After that, Mppa was converted to pyropheophorbide-a (Ppa) by treatment with 50% sulfuric acid. Finally, phototoxicity and dark toxicity of purified Ppa in two different cell lines, TC-1 and CaSki, were examined by MTT assay. The results suggest that Ppa is more toxic to TC-1 cell line than CaSki cell line. In vivo, the photosensitizing efficiency of Ppa was also higher than those of unloaded PS. These results indicate the potential of Ppa in PDT.

Size-dependent photodynamic activity of gold nanoparticles conjugate of water soluble purpurin-18-N-methyl-d-glucamine

Gold nanoparticles (GNPs) conjugates of water soluble ionic photosensitizer (PS), purpurin-18-N-methyl-D-glucamine (Pu-18-NMGA), were synthesized using various molar ratios between HAuCl₄ and Pu-18-NMGA without adding any particular reducing agents and surfactants. The PS-GNPs conjugates showed long wavelength absorption of range 702–762 nm, and their different shapes and diameters depend on the molar ratios used in the synthesis. In vitro anticancer efficacy of the PS-GNPs conjugates was investigated by MTT assay against A549 cells, resulting in higher photodynamic activity than that of the free Pu-18-NMGA. Among the PS-GNPs conjugates, the GNPs conjugate from the molar ratio of 1 : 2 (Au(III): Pu-18-NMGA) exhibits the highest photodynamic activity corresponding to bigger size (~60 nm) of the GNPs conjugate which could efficiently transport the PS into the cells than that of smaller size of the GNPs conjugate.

Synthesis of di-pyropheophorbide-a-platinum(II) complex and the in vitro cytotoxicity against TC-1 tumor cells

This report focuses on the conjugation of a chemotherapeutic drug and photodynamic therapy (PDT) agent with the intention of obtaining an optimal anticancer agent for use in combination cancer treatment. We have used pyropheophorbide-a (PPa) as a PDT agent, which was linked with ethylenediamine using carbodimide/N-hydroxysuccinicimide coupling reagents to obtain a resulting reactive amine group. Next, the free amine-bearing PPa and potassium tetrachloroplatinate (K2PtCl4) were reacted in aqueous solution to obtain PPa-cisplatin complex. Subsequently, the PPa-based platinum complex was characterized through several methods including NMR spectroscopy, mass spectrometer and UV absorption spectroscopy and its in vitro cytotoxicity and cellular uptake were evaluated on the TC-1 cancer cell line. The results indicated that the conjugate has a greater cytotoxic effect in the dark than cisplatin, even though its phototoxic effect was slightly lower than that of free photosensitizer; in addition, the cellular uptake of complex at 0.125 and 0.25 μM was higher than that of free photosensitizer.

In vitro phototoxicity and dark-toxicity of a novel synthesized pyropheophorbide-a-paclitaxel conjugate against cancer cell lines

Synthesis of pyropheophorbide-a-paclitaxel (PPa-PTX) conjugate was performed in high yield with the aim of searching for an optimal agent for cancer treatment. After synthesis, the conjugate was confirmed to be linked through an ester bond at the 2′ position of the paclitaxel moiety using multi-nuclear magnetic resonance spectroscopy. Phototoxicity of PPa and PPa-PTX conjugate, as well as PTX, was evaluated with three human cancer cell lines (HeLa, CaSki and TC-1). The new conjugate at 0.01–0.06 μM displayed 20–40% higher phototoxicity in HeLa and CaSki cell lines than free PPa and PTX. Furthermore, cellular uptake of these bio-molecules was examined by confocal laser scanning microscopy. Although PPa-PTX showed a delayed uptake compared to PPa, it penetrated completely into cells within 24 h incubation.

Synthesis and photodynamic activities of novel water soluble purpurin-18-N-methyl-D-glucamine photosensitizer and its gold nanoparticles conjugate

A new type of water soluble ionic photosensitizer (PS), purpurin-18-N-methyl-D-glucamine (Pu-18-NMGA) has been synthesized and it was conjugated into gold nanoparticles (GNPs) stabilized by the PS without adding any particular reducing agents and surfactants. In vitro anticancer efficacy of the PS and its PS–GNPs conjugate against A549 lung cancer cell lines was evaluated. The PS–GNPs conjugate based on water-soluble Pu-18-NMGA afforded good PDT efficacy which was three times greater than that of the water-soluble PS.

Synthesis of long-wavelength chlorins by chemical modification for methyl pyropheophorbide-a and their in vitro cell viabilities

A series of novel chlorophyll-a homologs with long wavelength absorption were synthesized via modification of methyl pyropheophorbide-a used as starting material. For introducing electron-withdrawing group methylenemalononitrile moiety was established on the periphery of modified chlorin by Knoevenagel reaction of malononitrile with formyl group at 3-, 15-position and 131-carbonyl group on the exocyclic ring. All of chlorins containing the methylenemalononitrile structure show Qy-absorption at more than 700 nm. Moreover, we have examined a preliminary in vitro photodynamic anticancer effect of these new derivatives on mouse sarcoma S-180 cell line.

Molecular geometries and spectra of methyl pyropheophorbide-a pyrazole derivatives: a density functional theory study

Density functional theory (DFT) electronic structure calculations were performed to predict the geometries of the chlorin macrocycle core in methyl pyropheophorbide-a pyrazole derivatives (e.g. HPMPPa and PPMPPa). These compounds are new photosensitizer materials that possess the dual function activity in photodynamic therapy. We found that the geometries of the two compounds were nearly the same, and that substitution of the pyrazole moieties at C31 -position of methyl pyropheophorbide-a did not have significant effects on the geometries of the chlorin macrocycle core. Excitation energies and oscillator strengths were computed by time-dependent DFT. The time-dependent DFT spectrum of HPMPPa and PPMPPa were not affected by the pyrazole substituent. To determine the hydrophilic effect of photosensitizers, we calculated the interaction energy between photosensitizer and water, and observed that the interaction energy of HPMPPa was higher than that of PPMPPa. We found that the interaction energy with specific wavelength (Q-bands) is an important factor to consider in the development of photodynamic therapy.

Synthesis of methyl pyropheophorbide-a pyrazole derivatives and their in vitro cell viabilities on A549 cells

Porphyrins and chlorins containing acetylacetone residues on the peripheral substituents are known to readily react with hydrazine derivatives to form porphyrin and chlorin derivatives possessing a pyrazole moiety. In this study, we have carried out the synthesis of methyl pyropheophorbide-a derivatives containing a pyrazole moiety on its peripheral position. Moreover, we have examined a preliminary in vitro effect of these new derivatives on A549 cancer cell in photodynamic therapy.

Gadolinium complexes of chlorin derivatives applicable for MRI contrast agents and PDT

One of the ultimate goals of contrast agent (CA) research in magnetic resonance imaging (MRI) is to identify tumor-seeking materials. Thus, cancer diagnosis by Photodynamic Therapy (PDT) using photosensitizer will be one of the best tools for cancer research. By linking paramagnetic gadolinium [ Gd(III) ] ion to tumor selective chlorin-based photosensitizers, the cancer cell can be easily detected with high sensitivity and cured by appropriate laser irradiation simultaneously. The synthesis of monomer and dimer chlorin derivatives, such as pyropheophorbide-a and purpurin systems, conjugated with Gd(III) diethylenetriaminepentaacetic acid (DTPA) by means of diethylene-triaminepentaacetic dianhydride (caDTPA) for the evaluation as CAs for MRI was described in the present study.

Hydrophobicity parameters (Log P) of glycoconjugated porphyrins for photodynamic therapy evaluated by reversed phase HPLC

Photodynamic therapy (PDT) is one of the most effective treatments for cancer. We synthesized and characterized a series of 16 glycoconjugated porphyrins using a modification of the Lindsey method in the presence of Zn ( OAc )2·2 H 2 O as a template. The Zn 2+ ion template strategy improved the yield about 3-fold in the case of meta-substituted tetraphenylporphyrins, and free-base porphyrins were obtaind almost quantitatively by demetalation with 4 M HCl . The hydrophobicity parameter (Log P) of these porphyrins was evaluated by reversed phase high-performance liquid chromatography (RP-HPLC). The Log P values ranged from +4.8 to +7.8, so that most of the compounds are amphiphilic. The effect of the glycopyranosyl unit on the hydrophobicity of these compounds is discussed on the basis of the Log P value.

New bacteriochlorin derivatives with a fused N-aminoimide ring

Upon interaction of hydrazine hydrate with bacteriopurpurin, the initially formed monohydrazide in an acidic medium readily reacts with the second carboxyl group to give a six-membered N-aminocycloimide of bacteriochlorin p6. The free amino group at the fused imide ring makes it easy to obtain N-alkyl and N-acyl derivatives. The compounds thus obtained exhibit high light-induced cytotoxicity on A549 human adenocarcinoma cells.

Efficient synthesis and in vitro photodynamic anticancer study of new purpurinimide-hydrazone conjugates

A series of new purpurinimide-hydrazone conjugates were synthesized, and their in vitro anticancer efficacy against A549 lung cancer cell lines was evaluated. It was found that the incorporation of the hydrazone group to the purpurinimide could increase their anticancer activities via a combination of photodynamic therapy and chemotherapy.

Synthesis, photophysical, electrochemical, tumor-imaging, and phototherapeutic properties of purpurinimide-N-substituted cyanine dyes joined with variable lengths of linkers

Purpurinimide methyl esters, bearing variable lengths of N-substitutions, were conjugated individually to a cyanine dye with a carboxylic acid functionality. The results obtained from in vitro and in vivo studies showed a significant impact of the linkers joining the phototherapeutic and fluorescence imaging moieties. The photosensitizer-fluorophore conjugate with a PEG linker showed the highest uptake in the liver, whereas the conjugate linked with two carbon units showed excellent tumor-imaging and PDT efficacy at 24 h postinjection. Whole body imaging and biodistribution studies at variable time points portrayed enhanced fluorescent uptake of the conjugates in the tumor compared to that in the skin. Interestingly, the conjugate with the shortest linker and the one joining with two carbon units showed faster clearance from normal organs, e.g., the liver, kidney, spleen, and lung, compared to that in tumors. Both imaging and PDT efficacy of the conjugates were performed in BALB/c mice bearing Colon26 tumors. Compared to the others, the short linker conjugate showed poor tumor fluorescent properties and as a corollary does not exhibit the dual functionality of the photosensitizer-fluorophore conjugate. For this reason, it was not evaluated for in vivo PDT efficacy. However, in Colon26 tumor cells (in vitro), the short linker was highly effective. Among the conjugates with variable linkers, the rate of energy transfer from the purpurinimide moiety to the cyanine moiety increased with deceasing linker length, as examined by femtosecond laser flash photolysis measurements. No electron transfer from the purpurinimide moiety to the singlet excited state of the cyanine moiety or from the singlet excited state of the cyanine moiety to the purpurinimide moiety occurred as indicated by a comparison of transient absorption spectra with spectra of the one-electron oxidized and one-electron reduced species of the conjugate obtained by spectroelectrochemical measurements.

Synthesis, spectroscopic, and in vitro photosensitizing efficacy of ketobacteriochlorins derived from ring-B and ring-D reduced chlorins via pinacol-pinacolone rearrangement

In this report, we present a regioselective oxidation of a series bacteriochlorins, which on reacting with either ferric chloride (FeCl(3)) or 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) yielded the corresponding ring-B or ring-D reduced chlorins. The effect of the number of electron-withdrawing groups present at the peripheral position, with or without a fused isocyclic ring (ring-E), did not make any significant difference in regioselective oxidation of the pyrrole rings. However, depending on the nature of substituents, the intermediate bis-dihydroxy bacteriochlorins on subjecting to pinacol-pinacolone reaction conditions gave various ketochlorins. The introduction of the keto-group at a particular position in the molecule possibly depends on the stability of the intermediate carbocation species. The newly synthesized bacteriochlorins show strong long-wavelength absorption and produced significant in vitro (Colon26 cells) photosensitizing ability. Among the compounds tested, the bacteriochlorins containing a keto-group at position 7 of ring-B with cleaved five-member isocyclic ring showed the best efficacy.