An LC–MS/MS method for determination of O6-benzylguanine and its metabolite O6-benzyl-8-oxoguanine in human plasma

O⁶-benzylguanine (O⁶BG) is an inhibitor of O⁶-alkylguanine-DNA alkyltransferase (AGT). It binds to AGT by transferring its benzyl moiety to the cysteine residue at the active site of the enzyme. O⁶BG synergizes the cytotoxic effects of alkylating agents by halting AGT-mediated DNA repair. O⁶-benzyl-8-oxoguanine (8-oxo-O⁶BG) is a metabolite of O⁶BG, which is an equally potent inhibitor of AGT. In this work, we report the development and validation of an LC–MS/MS method for simultaneous determination of O⁶BG and 8-oxo-O⁶BG in human plasma. O⁶BG and 8-oxo-O⁶BG along with the analog internal standard, pCl-O⁶BG, were extracted from alkalinized human plasma by liquid–liquid extraction using ethyl acetate, dried under nitrogen and reconstituted in the mobile phase. Reverse-phase chromatographic separation was achieved using isocratic elution with a mobile phase containing 80% acetonitrile and 0.05% formic acid in water at a flow rate of 0.600 ml/min. Quantification was performed using multiple-reaction-monitoring mode with positive ion-spray ionization. The linear calibration ranges of the method for O⁶BG and 8-oxo-O⁶BG were 1.25–250 ng/ml and 5.00–1.00 × 10³ ng/ml, respectively, with acceptable assay accuracy, precision, recovery and matrix factor. This method was applied to the measurement of O⁶BG and 8-oxo-O⁶BG in patient plasma samples from a prior phase I clinical trial.     

Synthesis,antibacterial activity,and docking studies of some novel N′-benzylidene-2-(2,4,5-trifluorophenyl)acetohydrazides

Research on Chemical Intermediates - An improved method was developed for synthesis of 2,4,5-trifluorobenzohydrazide derivatives through condensation of trifluorophenylacetohydrazide with different...     

Antimony(III) Halide-Assisted Stereospecific Coordination of Thione

The antimony halide-aided stereospecific coordination of a cyclic thiourea-type of ligand is observed for the first time. The antimony(III) imidazole thione complexes syn-[( L¹ )SbCl₃] ( syn- 1 ) and anti-[( L¹ )SbBr₃] ( anti- 2 ) have been synthesized in very good yield by the reaction between the spatially defined steric impact ligand [(IPaul)S] ( L¹ ) ([(IPaul)S]=1,3-bis(2,4-methyl-6-diphenyl phenyl)imidazole thione) and corresponding antimony halide. The stereoselective formation of complexes syn- 1 and anti- 2 has been confirmed by both NMR and single-crystal X-ray diffraction studies. Interestingly the stereospecific nature of syn- 1 and anti- 2 remains intact in solution. Furthermore, the thermal stability of antimony(III) imidazole thione complexes were examined by TGA analysis.     

Beyond carbohydrate binding: new directions in plant lectin research

Although for a long time carbohydrate binding property has been used as the defining feature of lectins, studies carried out mostly during the last two decades or so demonstrate that many plant lectins exhibit specific interactions with small molecules that are predominantly hydrophobic in nature. Such interactions, in most cases, appear to be at specific sites that do not interfere with the ability of the lectins to recognise and bind carbohydrates. Further, several of these ligands have binding affinities comparable to those for the binding of specific carbohydrates to the lectins. Given the ability of lectins to specifically recognise the glycocode (carbohydrate code) on different cell surfaces and distinguish between diseased and normal tissues, these additional sites may be viewed as potential drug carrying sites that could be exploited for targeted delivery to sites of choice. Porphyrin-lectin complexes are especially suited for such targeting since porphyrins are already under investigation in photodynamic therapy for cancer. This review will provide an update on the interactions of plant lectins with non-carbohydrate ligands, with particular emphasis on porphyrin ligands. The implications and potential applications of such studies will also be discussed.     

Fluorescence studies on the interaction of hydrophobic ligands with Momordica charantia (bitter gourd) seed lectin

The interaction of Momordica charantia (bitter gourd) seed lectin (MCL) with several nucleic acid bases has been investigated by monitoring changes induced in the protein fluorescence by ligand binding. Values of the binding constant, K_a were obtained as 1.1 × 10⁴, 1.56 × 10⁴ and 2.2 × 10³ M^?1 for adenine, cytosine and uracil, respectively. In addition, binding of 8-anilinonaphthalene 1-sulfonate (ANS) with MCL was investigated by fluorescence spectroscopy. Interaction with MCL at low pH results in a large enhancement of the fluorescence intensity of ANS with a concomitant blue shift in the emission λ_max, whereas at neutral and basic pH changes in both fluorescence intensity and emission maximum were very small, clearly suggesting that the MCL–ANS interaction is stronger at lower pH values. When excited at 295 nm in the presence of ANS, the protein fluorescence decreased with a concomitant increase in the emission intensity of ANS, suggesting resonance energy transfer from the tryptophan residues of MCL to ANS. Gel filtration profiles of MCL at pH values 2.0 and 7.4 are similar indicating that the tetrameric nature of MCL is retained even at low pH. Addition of lactose or adenine to MCL–ANS mixture did not alter the change in ANS fluorescence suggesting that lactose, adenine and ANS bind to MCL at independent and non-interacting sites. These results are relevant to understanding the functional role of MCL in the parent tissue.