Novel methyl helianthrones as photosensitizers: synthesis and biological evaluation

A combination of light, oxygen and a photosensitizer is used to induce death of cancer cells by photodynamic therapy. In this study, we have synthesized several new methyl helianthrone derivatives and compared their phototoxicity with that of hypericin. In contrast to hypericin, methyl helianthrones are soluble in aqueous solutions and have a broad range of light absorbance, which allows the use of polychromatic light. Structural modifications of methyl helianthrone demonstrated that substitution of hydrogen atoms of methyl helianthrone at Positions 2 and 5 with Br atoms or methylation of its phenolic hydroxyls, significantly increases the corresponding singlet oxygen quantum yield and their phototoxicity toward alphaT3-1, M2R and LNCaP cells. The phototoxicity of some of these compounds was similar to that of hypericin. Methyl helianthrones, like hypericin, accumulated mainly in the perinuclear region as evident by confocal microscopy. Irradiation of cells pretreated with methyl helianthrone derivatives generates intracellular reactive oxygen species and lipid free radicals, as shown by a fluorescentic probe and electron paramagnetic resonance methods, respectively. The phototoxicity of these methyl helianthrones as well as their ability to oxidize membrane lipids were significantly decreased on addition of specific Type-II inhibitors, suggesting the involvement of singlet oxygen as the main oxidant.     

Quantitative determination of chelators and their degradation products in mixed hazardous wastes from Tank 241-SY-101 using derivatization GC/MS

Considerable attention has been focused on chelators such as ethylenediaminetetraacetic acid (EDTA) and N-(2-hydroxyethyl)ethylenediaminetriacetic acid (HEDTA), which form water-soluble complexes with most heavy metals. Most radionuclides are included in this class of constituents. As a result, chelator complexes have become very important environmentally because of their tendency to enhance the mobility of heavy metals through the soil and potentially contaminate groundwater. In addition, there is a correlation between chelator concentration and crust formation/gas release. The chelators are a class of compounds whose low volatility and high polarity preclude analysis by gas chromatography/mass spectrometry (GC/MS) without prior derivatization. Waste samples from a double-shell storage tank at Hanford were derivatized with BF₃/methanol and analyzed using GC/MS. Results indicate the presence of EDTA, HEDTA, nitrilotriacetic (NTA), and citric acid. Nitrosoiminodiacetic acid was identified and determined to be an artifact of the derivatization procedure; it is assumed to arise from nitrosation of iminodiacetic acid in the waste sample.     

THE EFFECT OF LIPOSOMES'' MEMBRANE COMPOSITION ON THE BINDING OF THE PHOTOSENSITIZERS HPD AND PHOTOFRIN II

Abstract— Photofrin II (PF-II) is the commercial name of the active photosensitizer which is used in photodynamic therapy of cancer. The effect of the composition of lipid membranes on the binding of PF-II was studied and compared to hematoporphyrin derivative (Hpd), which is a complex mixture of porphyrins and from which PF-II is separated. We find that increasing the content of cholesterol in the bilayer decreases the partitioning of PF-II into the bilayer, similar to what we have found earlier with Hpd. However, inserting DMPC or DPPC into the membrane, which was shown to decrease the binding of Hpd, causes the opposite trend with PF-H. A membrane fluidizer such as benzyl alcohol also has different effects on the membrane binding of Hpd and PF-II. The rate of binding of PF-II to a lipid membrane is about 10 times lower than that of Hpd. These results as well as I^- quenching of the fluorescence of the two porphyrins indicate that PF-II is immersed less homogeneously and deeper in the bilayer than Hpd. The unique additive-dependent binding of PF-II to lipid membranes calls for care in using Hpd as a model photosensitizer.     

A convenient oxazole C-2 protecting group: the synthesis of 4- and 5-substituted oxazoles via metalation of 2-triisopropylsilyloxazoles

[reaction: see text] Metalation of oxazoles at the 4 and 5 position was achieved after regioselective C-2 silyl protection. Removal of the protecting group was then accomplished under mild conditions allowing for a straightforward preparation of C-5 monosubstituted and C-4,5 disubstituted oxazoles. The first practical C-2 protecting group of oxazoles has been demonstrated.     

Effects of alkali metal halide salts on the hydrogen bond network of liquid water

Measurements of the oxygen K-edge X-ray absorption spectrum (XAS) of aqueous sodium halide solutions demonstrate that ions significantly perturb the electronic structure of adjacent water molecules. The addition of halide salts to water engenders an increase in the preedge intensity and a decrease in the postedge intensity of the XAS, analogous to those observed when increasing the temperature of pure water. The main-edge feature exhibits unique behavior and becomes more intense when salt is added. Density functional theory calculations of the XAS indicate that the observed red shift of the water transitions as a function of salt concentration arises from a strong, direct perturbation of the unoccupied molecular orbitals on water by anions, and does not require significant distortion of the hydrogen bond network beyond the first solvation shell. This contrasts the temperature-dependent spectral variations, which result primarily from intensity changes of specific transitions due to geometric rearrangement of the hydrogen bond network.     

Chemically modified "polar patch" mutants of subtilisin in peptide synthesis with remarkably broad substrate acceptance: designing combinatorial biocatalysts

A significant enhancement of the applicability of the serine protease subtilisin Bacillus lentus (SBL) in peptide synthesis was achieved by using the strategy of combined site-directed mutagenesis and chemical modification to create chemically modified mutant (CMM) enzymes. The introduction of polar and/or homochiral auxiliary substituents, such as X=oxazolidinones, alkylammonium groups, and carbohydrates at position 166 at the base of the primary specificity S(1) pocket created SBL CMMs S166C-S-X with strikingly broad structural substrate specificities. These CMMs are capable of catalyzing the coupling reactions of not only L-amino acid esters but also D-amino acid esters as acyl donors with glycinamide to give the corresponding dipeptides in good yields. These powerful enzymes are also applicable to the coupling of L-amino acid acyl donors with alpha-branched acyl acceptor, L-alaninamide. Typical increases in isolated yields of dipeptides of 60-80 % over SBL-WT (e.g. 0 % yield of Z-D-Glu-GlyNH(2) using SBL-WT-->74 % using S166C-S-(CH(2))(2) NMe(3) (+)) demonstrate the remarkable synthetic utility of this "polar patch" strategy. Such wide-ranging systems displaying broadened and therefore similarly high, balanced yields of products (e.g. 91 % Z-L-Ala-GlyNH(2) and 86 % yield of Z-D-Ala-GlyNH(2) using S166C-S-(3R,4S)-indenooxazolidinone) may now allow the use of biocatalysts in parallel library synthesis.     

Single-molecule fluorescence spectroscopy of TOTO on poly-AT and poly-GC DNA

Excited state lifetime and amplitude measurements were made on thiazole orange dimer (TOTO), a dimeric DNA-intercalating fluorophore, at single-molecule concentrations. As expected from previous study, the excited state lifetime of TOTO intercalated in DNA is dependent on the sequence of the double-stranded DNA, having values of 2.2 ns in poly-GC DNA and 1.8 ns in poly-AT DNA. The distribution of excited state lifetimes of single molecules of TOTO intercalated into oligonucleotides having varying proportions of poly-GC sequences relative to poly-AT sequences were analyzed as a function of the fraction of poly-GC. By using excited state lifetime distributions from the purely GC and purely AT oligonucleotides as a basis set, it was possible to estimate the GC content of oligonucleotides with intermediate GC composition to within a few percent error. This serves as a model for the analysis of equilibrium binding distributions in DNA using single-molecule methods.     

A dual-column HPLC method for the simultaneous determination of DHPG (9-[(1,3-dihydroxy-2-propoxy)methyl]guanine) and its mono and diesters in biological samples

A convenient method for the simultaneous determination of various DHPG species present in biological samples is presented. This method utilizes a cation exchange column (25 cm X 4.6 mm i.d.) coupled in series to a short reversed-phase column (5 cm X 4.6 mm i.d.). The mobile phase consists of methanol:0.005M ammonium phosphate buffer, pH 2.5. There is a large polarity difference between DHPG and its esters due to the non-polar side chain of the ester moiety. The simultaneous determination of the diesters, monoesters, and DHPG in these samples using only the cation exchange or the reversed-phase column is not possible without time-consuming gradient elution. In the reversed-phase mode alone, the esters are highly retained relative to DHPG, whereas the esters are only slightly retained on a cation exchange column and are insensitive to changes in pH and ionic strength of the mobile phase. However, a combination of these two columns provides interesting selectivity for these compounds and offers a unique way of controlling the retention times of these species relative to each other. The retention time of esters can be selectively altered (with respect to DHPG) by changing the composition of methanol in the mobile phase. In contrast, the retention time of DHPG is controlled by changing the buffer strength and pH of the mobile phase.     

Energetic and stereochemical effects of the protein environment on substrate: a theoretical study of methylmalonyl-CoA mutase

QM/MM methods were used to study the isomerization step from (2R)-methylmalonyl-CoA to succinyl-CoA. A pathway via a "fragmentation-recombination" mechanism is ruled out on energetic grounds. For the other radicalic pathway, involving an addition recombination step, geometries and vibrational contributions have been determined, and a barrier height of 11.70 kcal/mol was found. The effect of adjacent hydrogen-donating groups was found to reduce the energy barrier by 1-2 kcal/mol each and thus to provide a significant catalytic effect for this reaction. By means of molecular dynamics studies, the stereochemistry of the methylmalonyl-CoA mutase catalyzed reaction was examined. It is shown that TYR89 is essential for maintaining stereoselectivity of the abstraction of a hydrogen in the backreaction. The subsequent selective formation of one isomer of methylmalonyl-CoA is probably due to the presence of a bulky side chain.