Molecular tweezers with freely rotating linker and porphyrin moieties

Molecular tweezers were synthesised by using a microwave accelerated alkene plus cyclobutane epoxide reaction between norbornyl appended porphyrin moieties and a diepoxide functionalised phenyl diimide spacer. The tweezers contain several rotational degrees of freedom; about the porphyrin with respect to the norbornyl linker, and between the two norbornyl backbone sections. The ability of Zn(super)II metallated tweezer 1 to complex 1,4-diazabicyclo[2.2.2]octane (DABCO) was studied by UV/Vis and ¹H NMR spectroscopy and multivariate global spectral analysis. The system was found to form a strong 1:1 intramolecular complex (1:DABCO) with an association constant of K₁₁ = 8.1 × 10⁷ M⁻¹, transforming to a 1:2 open complex [1:(DABCO)₂] with K₁₂ = 2.7 × 10⁹ M⁻² at high concentrations of DABCO.Rhys B. Murphy, Duc-Truc Pham, Stephen F. Lincoln, and Martin R. Johnsto

Localization and Photodynamic Efficacy of Two Cationic Porphyrins Varying in Charge Distribution

Two meso-tetraphenylporphyrin derivatives bearing adjacent: 5,10-di[4-(N-trimethylaminophenyl)-15,20-diphenylporphyrin (DADP-a) or opposite: 5,15-di[4-(N-trimethylaminophenyl)-10,20-diphenylporphyrin (DADP-o) cationic-N-(CH3)3+ groups on two of the para-phenyl positions were examined with regard to photodynamic properties as a function of charge distribution. The two adjacent positive charges in the DADP-a structure result in a molecular distortion (asymmetry), likely from electrostatic repulsion. This could be responsible for the unusual interaction of this compound with some solvents and detergent micelles. In contrast, DADP-o is a much more symmetric molecule. In a cellular environment, fluorescence spectra of the two agents were essentially identical. Subcellular localization played a major role in photodynamic efficacy. DADP-a localized in mitochondria, and irradiation of photosensitized cells (640-650 nm) resulted in a rapid loss of the mitochondrial membrane potential (ΔΨm), usually a prelude to apoptotic cell death. In contrast, DADP-o localized in lysosomes, and extensive lysosomal photodamage was observed after irradiation. Both steady-state accumulation levels and absorbance spectra favored DADP-o, but the light dose required for a 90% cell kill was two-fold greater for DADP-o than for DADP-a, at a constant extracellular sensitizer concentration. These data indicate that, on a photons/cell basis, DADP-a was five-fold more efficacious. Fluorescence emission spectra in different solvents and detergents demonstrated a tendency for DADP-a association. We interpret these results to indicate partition of both drugs to membrane loci, with mitochondria being the more lethal site for photodamage

Synthesis of a porphyrin-labelled carboranyl phosphate diester: A potential new drug for boron neutron capture therapy of cancer

A boron-rich, water-soluble porphyrin conjugate was synthesized by coupling of two carboranyl alcohols with 2-chlorophenoxyphosphorus dichloride, followed by conjugation to an amine-functionalized tetraphenyl-porphyrin via an amide linkage

Synthesis of novel carboranylchlorins with dual application in boron neutron capture therapy (BNCT) and photodynamic therapy (PDT)

Total synthesis of carboranylchlorins 3 and 4, from readily available starting materials, are described and the molecular structures of two key intermediates are presented. Chlorins 3 and 4 show similar spectroscopic behavior but differ considerably in their solubility properties; whereas closo-carboranylchlorin 3 is completely insoluble in water, its nido derivative 4 has good water-solubility. Carboranylchlorin 3 absorbs in the red region of the optical spectrum (at λmax=642nm) six times more strongly than porphyrin 1, and displays a fluorescence emission band at λmax=651nm, upon excitation at 642nm. The water-soluble carboranylchlorin 4 also displays intense absorption and emission bands at λmax=642 and 651nm, respectively, in ethanol solution. It is concluded that carboranylchlorins 3 and 4 have higher promise for the dual application in PDT and BNCT than do comparable porphyrins. © 2004 Elsevier Ltd. All rights reserved

Synthesis and cellular studies of an octa-anionic 5,10,15,20-tetra[3,5- (nido-carboranylmethyl)phenyl]porphyrin (H\u3csub\u3e2\u3c/sub\u3eOCP) for application in BNCT

The total synthesis of 5,10,15,20-tetra[3,5-(carboranylmethyl)phenyl] porphyrins 2-5 containing 36-43% boron by weight are reported. All compounds were characterized by spectroscopic methods and, in the case of 2, by X-ray crystallography. The water-soluble nido-carboranylporphyrin 5 (H2OCP) was found to have low dark toxicity toward V79 lung fibroblasts (CS 50 ≥ 250 μM), to be readily taken up by human glioblastoma T98G cells in culture and to localize subcellularly preferentially in the cell lysosomes. In comparison with a known tetra(nido-carboranyl)porphyrin (6), H2OCP (5) is taken up slower and to a lower extent by T98G cells, possibly as a result of its higher hydrophilic character. The metal-free H 2OCP (5) was also found to accumulate to a higher extent in T98G cells compared with its zinc(II) complex analog 4. Our studies show that carboranylporphyrins bearing eight nido-carborane cages can still accumulate intracellularly and have low dark toxicity toward cells in culture, and therefore might have promise for application in BNCT. © 2004 Elsevier Ltd. All rights reserved