Michael J. Hall

B,O-chelated azadipyrromethenes as near-IR probes.

Complementary synthetic routes to a new class of near-IR fluorophores are described. These allow facile access (four synthetic steps) to the core fluorophore and substituted derivatives with emissions between 740 and 780 nm in good quantum yields.

Dispersal of Biofilms by Secreted, Matrix Degrading, Bacterial DNase

Microbial biofilms are composed of a hydrated matrix of biopolymers including polypeptides, polysaccharides and nucleic acids and act as a protective barrier and microenvironment for the inhabiting microbes. While studying marine biofilms, we observed that supernatant produced by a marine isolate of Bacillus licheniformis was capable of dispersing bacterial biofilms. We investigated the source of this activity and identified the active compound as an extracellular DNase (NucB). We have shown that this enzyme rapidly breaks up the biofilms of both Gram-positive and Gram-negative bacteria. We demonstrate that bacteria can use secreted nucleases as an elegant strategy to disperse established biofilms and to prevent de novo formation of biofilms of competitors. DNA therefore plays an important dynamic role as a reversible structural adhesin within the biofilm.

A potent nonporphyrin class of photodynamic therapeutic agent: cellular localisation, cytotoxic potential and influence of hypoxia

We have developed a totally new class of nonporphyrin photodynamic therapeutic agents with a specific focus on two lead candidates azadipyrromethene (ADPM)01 and ADPM06. Confocal laser scanning microscopy imaging showed that these compounds are exclusively localised to the cytosolic compartment, with specific accumulation in the endoplasmic reticulum and to a lesser extent in the mitochondria. Light-induced toxicity assays, carried out over a broad range of human tumour cell lines, displayed EC50 values in the micro-molar range for ADPM01 and nano-molar range for ADPM06, with no discernable activity bias for a specific cell type. Strikingly, the more active agent, ADPM06, even retained significant activity under hypoxic conditions. Both photosensitisers showed low to nondeterminable dark toxicity. Flow cytometric analysis revealed that ADPM01 and ADPM06 were highly effective at inducing apoptosis as a mode of cell death. The photophysical and biological characteristics of these PDT agents suggest that they have potential for the development of new anticancer therapeutics.

Vascular-targeted photodynamic therapy with BF2-chelated Tetraaryl-Azadipyrromethene agents: a multi-modality molecular imaging approach to therapeutic assessment.

Background:Photodynamic therapy (PDT) is a treatment modality for a range of diseases including cancer. The BF2-chelated tetraaryl-azadipyrromethenes (ADPMs) are an emerging class of non-porphyrin PDT agent, which have previously shown excellent photochemical and photophysical properties for therapeutic application. Herein, in vivo efficacy and mechanism of action studies have been completed for the lead agent, ADMP06.Methods:A multi-modality imaging approach was employed to assess efficacy of treatment, as well as probe the mechanism of action of ADPM06-mediated PDT.Results:Tumour ablation in 71% of animals bearing mammary tumours was achieved after delivery of 2 mg kg−1 of ADPM06 followed immediately by light irradiation with 150 J cm−2. The inherent fluorescence of ADPM06 was utilised to monitor organ biodistribution patterns, with fluorescence reaching baseline levels in all organs within 24 h. Mechanism of action studies were carried out using dynamic positron emission tomography and magnetic resonance imaging techniques, which, when taken together, indicated a decrease in tumour vascular perfusion and concomitant reduction in tumour metabolism over time after treatment.Conclusion:The encouraging treatment responses in vivo and vascular-targeting mechanism of action continue to indicate therapeutic benefit for this new class of photosensitiser.

Efficacy of a Marine Bacterial Nuclease against Biofilm Forming Microorganisms Isolated from Chronic Rhinosinusitis

Background The persistent colonization of paranasal sinus mucosa by microbial biofilms is a major factor in the pathogenesis of chronic rhinosinusitis (CRS). Control of microorganisms within biofilms is hampered by the presence of viscous extracellular polymers of host or microbial origin, including nucleic acids. The aim of this study was to investigate the role of extracellular DNA in biofilm formation by bacteria associated with CRS. Methods/Principal Findings Obstructive mucin was collected from patients during functional endoscopic sinus surgery. Examination of the mucous by transmission electron microscopy revealed an acellular matrix punctuated occasionally with host cells in varying states of degradation. Bacteria were observed in biofilms on mucosal biopsies, and between two and six different species were isolated from each of 20 different patient samples. In total, 16 different bacterial genera were isolated, of which the most commonly identified organisms were coagulase-negative staphylococci, Staphylococcus aureus and α-haemolytic streptococci. Twenty-four fresh clinical isolates were selected for investigation of biofilm formation in vitro using a microplate model system. Biofilms formed by 14 strains, including all 9 extracellular nuclease-producing bacteria, were significantly disrupted by treatment with a novel bacterial deoxyribonuclease, NucB, isolated from a marine strain of Bacillus licheniformis. Extracellular biofilm matrix was observed in untreated samples but not in those treated with NucB and extracellular DNA was purified from in vitro biofilms. Conclusion/Significance Our data demonstrate that bacteria associated with CRS form robust biofilms which can be reduced by treatment with matrix-degrading enzymes such as NucB. The dispersal of bacterial biofilms with NucB may offer an additional therapeutic target for CRS sufferers.

Circularly Polarized Luminescence from Helically Chiral N,N,O,O‐Boron‐Chelated Dipyrromethenes

Abstract Helically chiral N,N,O,O‐boron chelated dipyrromethenes showed solution‐phase circularly polarized luminescence (CPL) in the red region of the visible spectrum (λ em(max) from 621 to 663 nm). The parent dipyrromethene is desymmetrised through O chelation of boron by the 3,5‐ortho‐phenolic substituents, inducing a helical chirality in the fluorophore. The combination of high luminescence dissymmetry factors (|g lum| up to 4.7 ×10−3) and fluorescence quantum yields (Φ F up to 0.73) gave exceptionally efficient circularly polarized red emission from these simple small organic fluorophores, enabling future application in CPL‐based bioimaging.

A Convergent Approach toward the C1−C11 Subunit of Phoslactomycins and Formal Synthesis of Phoslactomycin B

The preparation of the C1-C11 subunit of phoslactomycins, and a formal synthesis of phoslactomycin B, were achieved by a convergent strategy involving the chelation-controlled addition of an alkynyl Grignard reagent to an alpha-alkoxy ketone. Catalytic enantioselective reductions of acetylenic ketones and a [2,3]-Wittig rearrangement were utilized as key steps to control the configuration of the C4, C5, and C9 stereocenters.

Mechanistic insight into the formation of tetraarylazadipyrromethenes.

The tetraarylazadipyrromethene chromophore class has gained increasing attention in the past decade for a diverse set of scientific interests and applications. The most direct synthetic route available for their generation is heating of 4-nitro-1,3-diarylbutan-1-ones with an ammonium source in an alcohol solvent. Despite the practical simplicity, the reaction pathway(s) for these conversions are lengthy and unclear. To gain insight into the steps involved, (15)N labeling experiments with MS and NMR analysis were utilized for conversion of 4-nitro-1,3-diphenylbutan-1-one 1 into tetraphenylazadipyrromethene 2 with (15)NH(4)OAc. To permit examination of later stages of the reaction sequence to 2, the (15)N-labeled potential intermediate 3,5-diphenyl-1H-pyrrol-2-amine 10 was synthesized. A study of the dimerization pathway utilizing (15)N-labeled 10 revealed an unprecedented nitrogen rearrangement in the final stages of the pathway involving a ring-opening/closing of a pyrrole ring. Utilizing (15)N labeling experiments we have shown that 2,4-diphenylpyrrole 8 can also react under the reaction conditions with 3,5-diphenyl-2H-pyrrol-2-imine 7 (from oxidation of 10) to produce 2. Overall in the conversion of 1 into 2, two related pathways are ongoing concurrently; the first involves a dimerization of 3,5-diphenyl-2H-pyrrol-2-imine 7, and the other a reaction of 7 with 2,4-diphenylpyrrole 8.

An LC/MS/MS method for stable isotope dilution studies of β-carotene bioavailability, bioconversion, and vitamin A status in humans

Isotope dilution is currently the most accurate technique in humans to determine vitamin A status and bioavailability/bioconversion of provitamin A carotenoids such as β-carotene. However, limits of MS detection, coupled with extensive isolation procedures, have hindered investigations of physiologically-relevant doses of stable isotopes in large intervention trials. Here, a sensitive liquid chromatography-tandem mass spectrometry (LC/MS/MS) analytical method was developed to study the plasma response from coadministered oral doses of 2 mg [13C10]β-carotene and 1 mg [13C10]retinyl acetate in human subjects over a 2 week period. A reverse phase C18 column and binary mobile phase solvent system separated β-carotene, retinol, retinyl acetate, retinyl linoleate, retinyl palmitate/retinyl oleate, and retinyl stearate within a 7 min run time. Selected reaction monitoring of analytes was performed under atmospheric pressure chemical ionization in positive mode at m/z 537→321 and m/z 269→93 for respective [12C]β-carotene and [12C] retinoids; m/z 547→330 and m/z 274→98 for [13C10]β-carotene and [13C5] cleavage products; and m/z 279→100 for metabolites of [13C10]retinyl acetate. A single one-phase solvent extraction, with no saponification or purification steps, left retinyl esters intact for determination of intestinally-derived retinol in chylomicrons versus retinol from the liver bound to retinol binding protein. Coadministration of [13C10]retinyl acetate with [13C10]β-carotene not only acts as a reference dose for inter-individual variations in absorption and chylomicron clearance rates, but also allows for simultaneous determination of an individuals vitamin A status.

Diastereoselective synthesis of functionalised carbazoles via a sequential Diels–Alder/ene reaction strategy

An operationally simple one-pot, three-component, diastereoselective synthesis of saturated carbazoles and related pyridazino[3,4-b]indoles, based on two sequential intermolecular pericyclic reactions, is described. The reaction sequence involves an intermolecular Diels–Alder (D–A) reaction of a 3-vinyl-1H-indole, containing an electron withdrawing N-protecting group, with a suitable dienophile. Due to the electron withdrawing nature of the N-protecting group the resultant D–A cycloadducts are sufficiently stabilised to allow for a subsequent in situ diastereospecific intermolecular ene reaction to take place with an added enophile, generating functionalised carbazoles with relative stereocontrol of up to four stereocentres.