A comparison of the binding of metal complexes to duplex and quadruplex DNA

Electrospray ionisation mass spectrometry (ESI-MS) and circular dichroism (CD) spectroscopy were used to compare the binding of mononuclear nickel, ruthenium and platinum complexes to double stranded DNA (dsDNA) and quadruplex DNA (qDNA). CD studies provided evidence for the binding of intact complexes of all three metal ions to qDNA. ESI mass spectra of solutions containing platinum or ruthenium complexes and qDNA showed evidence for the formation of non-covalent complexes consisting of intact metal molecules bound to DNA. However, the corresponding spectra of solutions containing nickel complexes principally contained ions consisting of fragments of the initial nickel molecule bound to qDNA. In contrast ESI mass spectra of solutions containing nickel, ruthenium or platinum complexes and dsDNA only showed the presence of ions attributable to intact metal molecules bound to DNA. The fragmentation observed in mass spectral studies of solutions containing nickel complexes and qDNA is attributable to the lower thermodynamic stability of the former metal complexes relative to those containing platinum or ruthenium, as well as the slightly harsher instrumental conditions required to obtain spectra of qDNA. This conclusion is supported by the results of tandem mass spectral studies, which showed that ions consisting of intact nickel complexes bound to qDNA readily undergo fragmentation by loss of one of the ligands initially bound to the metal. The ESI-MS results also demonstrate that the binding affinity of each of the platinum and ruthenium complexes towards qDNA is significantly less than that towards dsDNA.     

Enhanced mass resolution method development, validation and assay application to support preclinical studies of a new drug candidate

A very highly sensitive and highly selective liquid chromatographic/tandem mass spectrometric (LC/MS/MS) method was developed to evaluate and quantify a new drug candidate in different biological matrices. Following a simple plasma protein precipitation using acetonitrile, the post-treatment samples were analyzed on a C18 column interfaced with a new generation of triple-quadrupole mass spectrometer. The recently introduced triple-quadrupole mass spectrometer, the TSQ Quantum Ultra, with enhanced mass-resolution capability, demonstrated improved sensitivity (0.05 ng/mL), coupled with suitable accuracy and precision, over a broad linear dynamic range (0.05-1000 ng/mL). A comparison of the assay performance data (dynamic range, calibration curve equation, precision and accuracy) of the enhanced resolution method against a unit resolution method under optimized conditions showed the performance improvement of the enhanced mass resolution method for bioanalytical high-throughput applications. The enhanced mass resolution method herein described was successfully applied to the evaluation of the pharmacokinetic profile of a new drug candidate in rat, rabbit and dog plasma samples.     

Solvothermal Synthesis and Crystal Structure of the New Layered Thioantimonate(III) [Ni(C4H13N3)2]9Sb22S42 · 0.5H2O: Interconnection of the SbS3, SbS4, and SbS5 Primary Building Units Yielding the Very Large Sb30S30 Heteroring

The novel thioantimonate(III) [Ni(dien)₂]₉Sb₂₂S₄₂ · 0.5H₂O was synthesised under solvothermal conditions by reacting elemental Ni, Sb and S in an aqueous solution of diethylenetriamine (dien) (80%). The compound crystallises in the triclinic space group P1¯, a = 8.997(2) Å, b = 15.293(3) Å, c = 34.434(7) Å, α = 85.51(3)°, β = 84.16(3)°, γ = 83.54(3)°, V = 4672.7 (16) ų, Z = 1. The layered [Sb₂₂S₄₂^18—] anion in [Ni(dien)₂]₉Sb₂₂S₄₂ · 0.5H₂O is composed of nine SbS₃ trigonal pyramids, one SbS₄ and one SbS₅ unit. The interconnection of these units by sharing common S atoms yields Sb‐S heterorings of different sizes. Besides the smaller Sb₂S₂ and Sb₃S₃ rings a very large Sb₃₀S₃₀ heteroring is observed. The structure directing effect of the [Ni(dien)₂]²⁺ cations is obvious as they are located above and below the pores of the anion. The nine [Ni(dien)₂]²⁺ cations exhibit different conformations. All Ni²⁺ cations are in an octahedral environment of six N atoms of two dien ligands. The anions and cations are stacked perpendicular to [100] in an alternating fashion.     

Nannocystin A: an Elongation Factor 1 Inhibitor from Myxobacteria with Differential Anti‐Cancer Properties

Cultivation of myxobacteria of the Nannocystis genus led to the isolation and structure elucidation of a class of novel cyclic lactone inhibitors of elongation factor 1. Whole genome sequence analysis and annotation enabled identification of the putative biosynthetic cluster and synthesis process. In biological assays the compounds displayed anti‐fungal and cytotoxic activity. Combined genetic and proteomic approaches identified the eukaryotic translation elongation factor 1α (EF‐1α) as the primary target for this compound class. Nannocystin A ( 1 ) displayed differential activity across various cancer cell lines and EEF1A1 expression levels appear to be the main differentiating factor. Biochemical and genetic evidence support an overlapping binding site of 1 with the anti‐cancer compound didemnin B on EF‐1α. This myxobacterial chemotype thus offers an interesting starting point for further investigations of the potential of therapeutics targeting elongation factor 1.