Regioselective synthesis and photophysical and electrochemical studies of 20-substituted cyanine dye-purpurinimide conjugates: incorporation of Ni(II) into the conjugate enhances its tumor-uptake and fluorescence-imaging ability.

We report herein a simple and efficient approach to the synthesis of a variety of meso-substituted purpurinimides. The reaction of meso-substituted purpurinimide with N-bromosuccinimide regioselectively introduced a bromo functionality at the 20-position, which on further reaction with a variety of boronic acids under Suzuki reaction conditions yielded the corresponding meso-substituted analogues. Interestingly, the free base and the metalated analogues showed remarkable differences in photosensitizing efficacy (PDT) and tumor-imaging ability. For example, the free-base conjugate showed significant in vitro PDT efficacy, but limited tumor avidity in mice bearing tumors, whereas the corresponding Ni(II) derivative did not produce any cell kill, but showed excellent tumor-imaging ability at a dose of 0.3 µmol kg(-1) at 24, 48, and 72 h post-injection. The limited PDT efficacy of the Ni(II) analogue could be due to its inability to produce singlet oxygen, a key cytotoxic agent required for cell kill in PDT. Based on electrochemical and spectroelectrochemical data in DMSO, the first one-electron oxidation (0.52 V vs. SCE) and the first one-electron reduction (-0.57-0.67 V vs. SCE) of both the free base and the corresponding Ni(II) conjugates are centered on the cyanine dye, whereas the second one-electron reduction (-0.81 V vs. SCE) of the two conjugates is assigned to the purpurinimide part of the molecule. Reduction of the cyanine dye unit is facile and occurs prior to reduction of the purpurinimide group, which suggests that the cyanine dye unit as an oxidant could be the driving force for quenching of the excited triplet state of the molecules. An interaction between the cyanine dye and the purpurinimide group is clearly observed in the free-base conjugate, which compares with a negligible interaction between the two functional groups in the Ni(II) conjugate. As a result, the larger HOMO-LUMO gap of the free-base conjugate and the corresponding smaller quenching constant is a reason to decrease the intramolecular quenching process and increase the production of singlet oxygen to some degree.

Butanolides from methanolic extract of Litsea glutinosa.

Phytochemical investigations of a MeOH extract obtained from the heartwoods of the Litsea glutinosa (Lauraceae) led to the isolation and characterization of four new butenolides, (3R,4S,5S)-2-hexadecyl-3-hydroxy-4-methylbutanolide 1, litsealactone C (2), and litsealactone D (4), litsealactone G (5), and a new benzoic acid derivative named eusmoside C (3). The structures of these compounds were elucidated on the basis of spectral studies.

Flavonoids: A versatile source of anticancer drugs.

An exponential increase in the number of studies investigating how different components of the diet interact at the molecular and cellular level to determine the fate of a cell has been witnessed. In search for anticancer drugs compelling data from laboratories, epidemiologic investigations, and human clinical trials showed that flavonoids have important effects on cancer chemoprevention and chemotherapy. In many molecular mechanisms of action for prevention against cancer, flavonoids play a major role by interacting between different types of genes and enzymes. Many mechanisms of action have been identified, including carcinogen inactivation, antiproliferation, cell cycle arrest, induction of apoptosis, inhibition of angiogenesis, antioxidation, and reversal of multidrug resistance or a combination of these mechanisms. This review focuses on the anticancer activity of flavonoids as well as their molecular mechanisms, including the treatment of mammary and prostate cancer. This review also highlights some advanced derivatives of flavonoids, which play an important role against cancer.

Indium as a central metal enhances the photosensitizing efficacy of benzoporphyrin derivatives.

Compared to benzoporphyrin derivative-dimethyl ester (BPD-DME) and its 8-(1'-hexyloxy)ethyl analog the corresponding In(III) complexes showed enhanced in vitro photosensitizing efficacy in Colon26 tumor cells, which could be due to their higher singlet oxygen producing ability. In both organic (methanol) and aqueous Bovine Calf Serum (17% BCS) solutions the metalated analogs were significantly more stable than the parent photosensitizers. Presence of Indium as a central metal gave 13-25 nm hypsochromic shift to the long wavelength absorption band with reduced absorption and fluorescence intensity. The insertion of metal did not produce any difference in intracellular localization of the photosensitizers and were mainly localized in mitochondria.

Remarkable features of the McMurry reaction conditions in dimerization of formyl- and 2-formylvinylpurpurinimides. Electrochemistry of monomeric Ni(II) purpurinimide and the corresponding dyads.

To investigate the electrochemical properties of purpurinimide dyads and electron transfer sites for their reduction and oxidation, a series of dimers with variable C-C linkages were synthesized. For the preparation of these novel structures, the formyl and 2-formylvinyl substituents were regioselectively introduced at positions 3 and 20 of Ni(II) purpurinimides by the Vilsmeier reaction. The Ni(II) complexes were then subjected to the McMurry reaction under two different conditions with unexpected results. For example, the reaction of formyl purpurinimides with TiCl(3)(DME)(1.5) failed to produce the desired C-C dimers, and the starting compounds were recovered almost quantitatively. Under similar reaction conditions, the 20-(2-formylvinyl)purpurinimide also did not dimerize but produced instead unexpected benzoisobacteriochlorins via an intramolecular cyclization. However, treatment of the 3-formyl- and 20-formylpurpurinimides with TiCl(4)/Zn produced corresponding dimers linked with one double bond (trans) in modest yields. Under similar conditions, Ni(II) purpurinimides containing a 2-formylvinyl substituent either at position 3 or at position 20 afforded the respective C-C dimers, where the purpurinimide moieties were joined with a trans-trans-trans hexatriene linker. Molecular modeling data suggest that the nature of the conformational energy difference found in all trans vs trans-cis-trans conformers of the dimers connected by a hexatriene linker at the meso- or beta-position of the macrocycle is not because of the intrinsic conformational energy difference of the linker region, which is identical for both dimers.

Highly selective synthesis of the ring-B reduced chlorins by ferric chloride-mediated oxidation of bacteriochlorins: effects of the fused imide vs isocyclic ring on photophysical and electrochemical properties.

The oxidation of bacteriopyropheophorbide with ferric chloride hexahydrate or its anhydrous form produced the ring-D oxidized (ring-B reduced) chlorin in >95% yield. Replacing the five-member isocyclic ring in bacteriopyropheophorbide- a with a fused six-member N-butylimide ring system made no difference in regioselective oxidation, and the corresponding ring-B reduced chlorin was isolated in almost quantitative yield. When the oxidant was replaced by 2,3-dichloro-5,6-dicyano-p-benzoquinone, which is frequently used at the oxidizing stage of the porphyrin synthesis, the ring-B oxidized (ring-D reduced) chlorins were obtained. With both ring-B reduced and ring-D reduced chlorins in hand, their photophysical and electrochemical properties were examined and compared for the first time. The ring-B reduced chlorine 20, with a fused six-member N-butylimide ring, exhibits the most red-shifted absorption band (at lambda(max) = 746 nm), the lowest fluorescence quantum yield (4.5%), and the largest quantum yield of singlet oxygen formation (67%) among the reduced ring-B and ring-D chlorins investigated in this study. Measurements of the one-electron oxidation and reduction potentials show that compound 20 is also the easiest to oxidize among the examined compounds and the third easiest to reduce. In addition, the 1.62 eV HOMO-LUMO gap of 20 is the smallest of the examined compounds, and this agrees with values calculated using the DFT method. Spectroelectrochemical measurements afforded UV-visible absorption spectra for both the radical cations and radical anions of the examined chlorins. The ring-B reduced compound 20, with a fused six-member N-butylimide ring, is regarded as the most promising candidate in this study for photodynamic therapy because it has the longest wavelength absorption and the largest quantum yield of singlet oxygen formation among the compounds investigated.

Methyl pyropheophorbide-a analogues: potential fluorescent probes for the peripheral-type benzodiazepine receptor. Effect of central metal in photosensitizing efficacy.

Pyropheophorbides and their metal complexes were synthesized to investigate their applications as nonradioactive peripheral benzodiazepine receptor (PBR) binding probes and photosensitizers for use in photodynamic therapy. They were found to be localized in mitochondria and showed significant binding to PBR. In some cases, the PBR binding values were similar to that for 17 (PK11195, 1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)isoquinoline-3-carboxamide). However, no direct correlation between 17 displacement ability and photosensitizing efficacy of photosensitizers was observed.

Chlorophyll-a analogues conjugated with aminobenzyl-DTPA as potential bifunctional agents for magnetic resonance imaging and photodynamic therapy.

A clinically relevant photosensitizer, 3-devinyl-3-(1-hexyloxyethyl)pyropheophorbide-a (HPPH, a chlorophyll-a derivative), was conjugated with Gd(III)-aminobenzyl-diethylenetriaminepentaacetic acid (DTPA), an experimental magnetic resonance (MR) imaging agent. In vivo reflectance spectroscopy confirmed tumor uptake of HPPH-aminobenzyl-Gd(III)-DTPA conjugate was higher than free HPPH administered intraveneously (iv) to C3H mice with subcutaneously (sc) implanted radiation-induced fibrosarcoma (RIF) tumor cells. In other experiments, Sprague-Dawley (SD) rats with sc implanted Ward Colon Carcinoma cells yielded markedly increased MR signal intensities from tumor regions-of-interest (ROIs) 24 h post-iv injection of HPPH-aminobenzyl-Gd(III)-DTPA conjugate as compared to unconjugated HPPH. In both in vitro (RIF tumor cells) and in vivo (mice bearing RIF tumors and rats bearing Ward Colon tumors) the conjugate produced significant increases in tumor conspicuity at 1.5 T and retained therapeutic efficacy following PDT. Also synthesized were a series of novel bifunctional agents containing two Gd(III) atoms per HPPH molecule that remained tumor-avid and PDT-active and yielded improved MR tumor conspicuity compared to their corresponding mono-Gd(III) analogues. Administered iv at a MR imaging dose of 10 micromol/kg, these conjugates produced severe skin phototoxicity. However, by replacing the hexyl group of the pyropheophorbide-a with a tri(ethylene glycol) monomethyl ether (PEG-methyl ether), these conjugates produced remarkable MR tumor enhancement at 8 h post-iv injection, significant tumoricidal activity (80% of mice were tumor-free on day 90), and reduced skin phototoxicity compared to their corresponding hexyl ether analogues. The poor water-solubility characteristic of these conjugates was resolved by incorporation into a liposomal formulation. This paper presents the synthesis of tumor-avid contrast enhancing agents for MR imaging and thus represents an important milestone toward improving cancer diagnosis and tumor characterization. More importantly, this paper describes a new family of bifunctional agents that combine two modalities into a single cost-effective "see and treat" approach, namely, a single agent that can be used for contrast agent-enhanced MR imaging followed by targeted photodynamic therapy.

Structural modifications of plumieride isolated from Plumeria bicolor and the effect of these modifications on in vitro anticancer activity.

Plumieride was isolated as one of the major components from the biologically active methanolic extract of the bark of Plumeria bicolor (family Apocynaceae). For investigating the effect of substituents on cytotoxic activity it was modified into a series of compounds. Replacing the methyl ester functionality of plumieride with alkyl amides of variable carbon units improved the cytotoxic activity, and a correlation between overall lipophilicity and cytotoxic activity was observed. In plumieride, the glucose moiety was converted into a di- and trisaccharide by following the protection and deprotection approach, and the resulting compounds produced enhanced cytotoxicity. However, these compounds were found to be less effective than plumeiride containing a dodecyl (12 carbon units) amide group. Among all of the derivatives, the naturally occurring plumieride showed the least cytotoxicity (50% cell kill = 49.5 microg/mL), and the dodecyl amide analogue of plumieridepentaacetate produced the best efficacy (50% cell kill = 11.8 microg/mL). The di- and trisaccharide analogues were found to be slightly less effective than the dodecyl derivative (50% cell kill = 15-17 microg/mL). The in vitro cytotoxicity of the plumieride analogues was determined in radiation-induced fibrosarcoma (RIF) tumor cells.

Purpurinimide-fullerene dyads: introduction of fullerene moiety at various peripheral positions of the purpurinimide system.

[reaction: see text] Fullerene was regioselectively introduced at various peripheral positions of N-hexyl-purpurinimide for photoinduced electron transfer studies. Remarkably different effects of the position of the fullerene moiety in the formation of atropisomers were observed.

Functionalization of OEP-based benzochlorins to develop carbohydrate-conjugated photosensitizers. Attempt to target beta-galactoside-recognized proteins.

meso-(2-Formylvinyl)octaethylporphyrin on reaction with cyanotrimethylsilane in the presence of various catalysts [copper triflate [Cu(OTf)(2)], indium triflate [In(OTf)(3)], or magnesium bromide diethyl etherate (MgBr(2).Et(2)O)] produced a mixture of the intermediate 3-hydroxy-3-cyanopropenoporphyrin, the corresponding trimethylsilyl ether derivative, and the unexpected propenochlorins. The yields of the reaction products were found to depend on the reaction conditions and the catalysts used. The intermediate porphyrins on treatment with concentrated sulfuric acid yielded the free-base cyanobenzochlorins in major quantity along with several other novel benzochlorins as minor products. Reduction of ethyl-3-hydroxy-1-pentenoate-porphyrin with DIBAL-H/NaBH(4) and subsequent acid treatment provided the corresponding free-base 10(3)-(2-hydroxyethyl)benzochlorin, which upon a sequence of reactions gave a free-base benzochlorin bearing a carboxylic acid functionality in good yield. It was then condensed with a variety of carbohydrates (glucosamine, galactosamine, and lactosamine), and the related conjugates were screened using the galectin-binding-ability assay. Among the carbohydrate conjugates investigated, the lactose and galactose analogues displayed the galectin-binding ability with an enhancement of about 300-400-fold compared to lactose. In preliminary studies, all photosensitizers (with or without carbohydrate moieties) were found to be active in vitro [radiation-induced fibrosarcoma (RIF) tumor cells]. However, the cells incubated with lactose (known to bind to beta-galactoside-recognized proteins) prior to the addition of the photosensitizers containing the beta-galactose moiety (e.g., galactose and lactose) produced a 100% decrease in their photosensitizing efficacy. Under similar experimental conditions, benzochlorin without a beta-galactoside moiety or the related glucose conjugate did not show any inhibition in its photosensitizing efficacy. These results in combination with the galectin-binding data indicate a possible beta-galactoside-recognized protein specificity of the galactose- and lactose-benzochlorin conjugates.

Synthesis, comparative photosensitizing efficacy, human serum albumin (site II) binding ability, and intracellular localization characteristics of novel benzobacteriochlorins derived from vic-dihydroxybacteriochlorins.

In a sequence of reactions, methyl mesopyropheophorbide a, mesochlorin e(6) trimethyl ester, mesochlorin p(6) trimethyl ester, mesopurpurin-18-N-hexylimide methyl ester, and mesopurpurin-18-N-3,5-bis(trifluoromethyl)benzylimide methyl ester were synthesized from chlorophyll-a. These chlorins on reacting with osmium tetraoxide produced the corresponding vic-dihydroxybacteriochlorins. The 8-vinylchlorins obtained by refluxing the related vic-dihydroxybacteriochlorins in o-dichlorobenzene were individually treated with dimethylacetylenedicarboxylate (DMAD) under Diels-Alder reaction conditions. The intermediate adducts on 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) treatment rearranged to the corresponding stable benzobacteriochlorins, exhibiting the longest wavelength absorption in the range of 737 to 805 nm. In preliminary in vitro (RIF tumor cells) and in vivo screening (C3H/HeJ mice bearing RIF tumors), some of these compounds were found to be quite effective. Under similar treatment conditions (drug dose: 5.0 micromol/kg; light dose: 135 J/cm(2), tumors were exposed to light for 30 min at 24 h postinjection), the benzobacteriochlorins containing N-substituted-imide ring system produced enhanced photosensitizing efficacy with limited skin phototoxicity. These compounds were also found to bind to site II of human serum albumin (HSA). However, no correlation between the binding constant values and photosensitizing efficacy was observed. A competitive intracellular localization study of these novel structures with Rhodamine-123 (a mitochondrial probe) indicated their preferential localization in mitochondria, without producing any specific displacement of (3)H-PK11195 (PBR probe, (3)H-labeled 1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinoline carboxamide). These results suggest that the mitochondrial peripheral benzodiazepine receptor (PBR) is not the cellular binding site for this class of compounds.

Thermolysis of vic-dihydroxybacteriochlorins: effect of the nature of substrates in directing the formation of chlorin-chlorin dimers with fixed and flexible orientations and their preliminary in vitro photosensitizing efficacy.

The thermolysis products obtained by refluxing a series of vic-dihydroxychlorins in o-dichlorobenzene are characterized. Depending on the nature of substrates, this methodology provides an access for novel carbon-carbon linked chlorin-chlorin dimers and chlorin-porphyrin dimers with fixed and flexible orientations. The configuration of the linkers in the symmetrical and unsymmetrical dimers was confirmed by extensive NMR (COSY, ROESY) and molecular modeling studies. The molecular modeling studies of the energy-optimized dimers with flexible orientation confirmed that one of the chlorin units of the dimeric structure is tilted toward the opposite ring as evident by the shielding effect in the resonances of some of the protons in the (1)H NMR spectroscopy. Among the dimers with fixed orientation, compared to the free-base analogues, the related mono- and di-Zn(II) complexes produced a decreased fluorescence intensity, suggesting a possibility of the faster energy transfer via intersystem crossing (ISC) in the metalated derivatives than the corresponding free-base analogues to produce the corresponding excited triplet states. The photosensitizing efficacy of the monomers and the related dimers was also compared in radiation-induced fibrosarcoma (RIF) tumor cells at variable drug/light doses. In preliminary screening, compared to monomers, the corresponding carbon-carbon linked dimers produced enhanced photosensitizing efficacy.