Syntheses of emeraldin and purpurin-18 analogs as target-specific photosensitizers for photodynamic therapy

Rapid and Facile Synthesis of Isomaleimides: Dehydration of Maleamic Acids using Methanesulfonyl Chloride

The dehydration of maleamic acids using methanesulfonyl chloride as a dehydrating agent to selectively and rapidly (<15 min) generate isomaleimides is reported. A variety of maleamic acid derivatives produce the corresponding isomaleimides in good to excellent yields. Adaptation of this protocol under flow synthesis allows for similar efficiency and decreased reaction times (13 seconds residence time). It was also possible to convert maleic anhydride into the desired isomaleimide in a two-step, one-flask operation.

Production of bacteriopurpurin-18 phytyl ester from bacteriopheophytin a via allomerization by contact with titanium oxides in the presence of molecular oxygen

Incubation of bacteriopheophytin (BPhe) a, which was a demetalated pigment of bacteriochlorophyll a in photosynthetic bacteria, in CH2Cl2 in the presence of TiO2 particles with bubbling O2 in the dark produced a pigment absorbing 814nm. Detailed characterization of the novel pigment isolated from the CH2Cl2 suspension revealed that bacteriopurpurin-18 phytyl ester possessing an anhydride-type six-membered exocyclic E-ring was majorly formed by the treatment with TiO2 particles under oxygenic conditions. Oxidation of the bacteriochlorin ring in BPhe a, namely formations of derivatives of 3-acetyl pheophytin a and 3-acetyl protopheophytin a, can barely be detected through the conversion processes.

Advance in photosensitizers and light delivery for photodynamic therapy

The brief history of photodynamic therapy (PDT) research has been focused on photosensitizers (PSs) and light delivery was introduced recently. The appropriate PSs were developed from the first generation PS Photofrin (QLT) to the second (chlorins or bacteriochlorins derivatives) and third (conjugated PSs on carrier) generations PSs to overcome undesired disadvantages, and to increase selective tumor accumulation and excellent targeting. For the synthesis of new chlorin PSs chlorophyll a is isolated from natural plants or algae, and converted to methyl pheophorbide a (MPa) as an important starting material for further synthesis. MPa has various active functional groups easily modified for the preparation of different kinds of PSs, such as methyl pyropheophorbide a, purpurin-18, purpurinimide, and chlorin e6 derivatives. Combination therapy, such as chemotherapy and photothermal therapy with PDT, is shortly described here. Advanced light delivery system is shown to establish successful clinical applications of PDT. Phtodynamic efficiency of the PSs with light delivery was investigated in vitro and/or in vivo.

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.

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.

Characterization of porphyrins, chlorins, and bacteriochlorins formed via allomerization of bacteriochlorophyll a. Synthesis of highly stable bacteriopurpurinimides and their metal complexes

Allomerization of bacteriochlorophyll a (Bchl a) was studied under various reaction conditions. Bchl a on stirring with KOH/propanol produced an "unstable bacteriochlorin", which decomposed in acidic conditions to give a complex mixture containing bacteriopurpurin a as a principal component. The yields of other compounds varied and were found to be dependent on reaction condition. The structures of the isolated porphyrins, chlorins, and bacteriochlorins, related to Bchl a, were assigned on the basis of 1D, 2D NMR (ROESY), and mass spectroscopy analyses. The presence of fused anhydride rings in porphyrin, chlorin, and bacterichlorin systems showed a significant influence on their optical properties. Compared to bacteriochlorophyll a and bacteriopheophytin, the related structurally modified analogues, e.g., the bacteriopurpurin a, 13(1)/15(1)-N-alkyl isoimide, and the imide analogues were found to be more stable with a significant difference in spectroscopic properties. Bacteriochlorins containing anhydride, imide, or isoimide cyclic rings demonstrated a significant bathochromic shift of their Q bands in their electronic absorption spectra. Under basic conditions the formation of the 12-hydroxymethyl, 12-formyl, and 12-methylene analogues as byproducts from the 12-methyl-bacteriopurpurin-N-hexylimide could be due to subsequent oxidation of the vinylogous enolate intermediates. To investigate the effect of the central metal in the electronic spectra, the stable bacteriopurpurin-18-N-hexylimide was converted to a series of metal complexes [Zn(II), Cd(II), and Pd(II)] by following the direct or transmetalation approaches. Compared to the free-base analogue, these complexes showed a remarkable shift in their electronic absorption spectra.

Photochemical and electrochemical properties of zinc chlorin-C60 dyad as compared to corresponding free-base chlorin-C60, free-base porphyrin-C60, and zinc porphyrin-C60 dyads

The photochemical and electrochemical properties of four chlorin-C60 or porphyrin-C60 dyads having the same short spacer between the macrocycle and the fullerene are examined. In contrast with all the previous results on porphyrin-fullerene dyads, the photoexcitation of a zinc chlorin-C60 dyad results in an unusually long-lived radical ion pair which decays via first-order kinetics with a decay rate constant of 9.1 x 10(3) x s(-1). This value is 2-6 orders of magnitude smaller than values reported for all other porphyrin or chlorin donor-acceptor of the molecule dyad systems. The formation of radical cations of the donor part and the radical anion of the acceptor part was also confirmed by ESR measurements under photoirradiation at low temperature. The photoexcitation of other dyads (free-base chlorin-C60, zinc porphyrin-C60, and free-base porphyrin-C60 dyads) results in formation of the ion pairs which decay quickly to the triplet excited states of the chlorin or porphyrin moiety via the higher lying radical ion pair states as is expected from the redox potentials.

Purpurinimides as photosensitizers: effect of the presence and position of the substituents in the in vivo photodynamic efficacy

This study presents a novel approach for the regioselective synthesis of a series of alkyl ether analogues of purpurin-18-N-alkylimide. In the purpurinimide series, this is the first example which demonstrates that the presence and position of the substituents in the macrocycle makes a remarkable difference in the in vivo PDT efficacy.

Effect of substituents in directing the formation of benzochlorins and isobacteriochlorins in porphyrin and chlorin systems

[formula: see text] A first synthesis of free-base fluorinated benzochlorins by acid-catalyzed cyclization of 20-(2-trisiloxy-trifluoromethylvinyl)octaethylporphyrin++ + is achieved. Under similar reaction conditions, the purpurin-18-N-hexylimide analogues produced the corresponding fluorinated and nonfluorinated ethylidene-substituted isobacteriochlorins and fluorinated chlorin, respectively. The structure of the porphyrin based fluorinated benzochlorin was also confirmed by X-ray analysis.