Selective octabromination of tetraarylporphyrins based on meso-substituent identity: Structural and electrochemical studies

Synthesis and isolation of selectively brominated tetraarylporphyrin derivatives is reported. Treatment with bromine of meso-5,10,15,20-tetrakis(3,4,5-trimethoxyphenyl)porphyrin (1) or meso-5,10,15,20-tetrakis(3,5-di-[Formula: see text]-butyl-4-hydroxyphenyl)porphinatocopper(II) (2-Cu) yields products octabrominated at the 2,6-positions of meso-aryl substituents [5,10,15,20-tetrakis(2,6-dibromo-3,4,5-trimethoxyphenyl)porphyrin, [Formula: see text]Br81] or macrocyclic [Formula: see text]-positions. The latter of these ([Formula: see text]-brominated) was identified as the oxoporphyrinogen 2,3,7,8,12,13,17,18-octabromo-5,10,15,20- tetrakis(3,5-di-[Formula: see text]-butyl-4-oxo-cyclohexa-2,5-dienylidene)porphyrinogen 3 obtained due to the adventitious oxidation and demetalation of 2-Cu, which could be alkylated at its macrocyclic nitrogen atoms yielding N[Formula: see text],N[Formula: see text],N[Formula: see text],N[Formula: see text]-tetrakis(4-bromobenzyl)-2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(3,5-di-[Formula: see text]-butyl-4-oxo-cyclo hexa-2,5-dienylidene)porphyrinogen 4. The former compound [Formula: see text]Br81 was complexed with Zn(II) ([Formula: see text]Br81-Zn) or Cu(II) ([Formula: see text]Br81-Cu) and could also be subjected to further bromination yielding 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(2,6-dibromo-3,4,5-trimethoxyphenyl)porphyrin, Br[Formula: see text]1. The effect on the electrochemical properties of the 2,6-bromophenyl-substituted porphyrin compounds over the more highly brominated products was assessed.

Tumor-localizing and radiosensitizing properties of meso-tetra(4-nido-carboranylphenyl)porphyrin (H2TCP)

Background and Purpose: Boron Neutron Capture Therapy (BNCT) is a binary cancer treatment that exploits the short range particles released from a nuclear fission reaction involving the non-radioactive 10 B nucleus and low-energy neutrons for the destruction of tumor cells. In this perspective, porphyrins and phthalocyanines can represent a vehicle for the transport of significant amounts of boron to the neoplastic lesion. Material and Methods: B16F1 melanotic melanoma subcutaneously transplanted in C57/BL6 mice has been used as an in vivo model. Pharmacokinetic studies were performed by intratumoral and intravenous injection of a meso-substituted porphyrin containing 36 B atoms per molecule ( H 2 TCP ) and the distribution of H 2 TCP in the tumor was assessed by fluorescence microscopy analysis. The tumor-bearing mice were exposed to the radiation field for 20 min at a reactor power of 5 kW. Results: At 0.5 h after intratumoral administration or at 24 h after intravenous injection, the amount of 10 B in the tumor was found to be about 60 ppm and about 6 ppm, respectively. In spite of the different amounts of 10 B in the tumor at the time of irradiation, a very similar delay in tumor growth (5-6 days) was induced by neutron irradiation in the two groups of injected mice with respect to control mice. Conclusions: Our results demonstrate that a suitable boron-loaded porphyrin displays a significant affinity for subcutaneous tumors, and upon activation by thermal neutrons, can promote an important response even in a fairly aggressive and generally radioresistant tumor such as melanotic melanoma.