Utilization of a kinetic isotope effect to decrease decomposition of ceftriaxone in a mixture of D2O/H2O

The discovery of cephalosporin and demonstration of its improved stability in aqueous solution, as well as enhanced in vitro activity against penicillin-resistant organisms, were major breakthroughs in the development of β-lactam antibiotics. Although cephalosporins are more stable with respect to hydrolytic degradation than penicillins, they still experience a variety of chemical transformations. The present study offers an insight into the rates and mechanisms of ceftriaxone degradation at the therapeutic concentration in water, a mixture of water and deuterium oxide, and deuterium oxide itself at the neutral pH. Specific ceftriaxone degradation products were observed in aged samples (including a previously unreported dimer-type species), and by comparing the degradation rates in H₂O and D₂O, the observation of a kinetic isotope effect provided some valuable insight as to the nature of the initial ceftriaxone degradation. The effect of protium to deuterium isotope change on the degradation kinetics of ceftriaxone was evaluated using the method of initial rates based on HPLC analysis as well as by quantitative ¹H NMR spectroscopy. Moreover, computational analysis was utilized to get a molecular insight into chemical processes governing the ceftriaxone degradation and to rationalize the stabilizing effect of replacing H₂O with D₂O.

N-substituted benzimidazole acrylonitriles as in vitro tubulin polymerization inhibitors: Synthesis, biological activity and computational analysis

We present the design, synthesis and biological activity of novel N-substituted benzimidazole based acrylonitriles as potential tubulin polymerization inhibitors. Their synthesis was achieved using classical linear organic and microwave assisted techniques, starting from aromatic aldehydes and N-substituted-2-cyanomethylbenzimidazoles. All newly prepared compounds were tested for their antiproliferative activity in vitro on eight human cancer cell lines and one reference non-cancerous assay. N,N-dimethylamino substituted acrylonitriles 30 and 41, bearing N-isobutyl and cyano substituents placed on the benzimidazole nuclei, showed strong and selective antiproliferative activity in the submicromolar range of inhibitory concentrations (IC₅₀ 0.2-0.6 μM), while being significantly less toxic than reference systems docetaxel and staurosporine, thus promoting them as lead compounds. Mechanism of action studies demonstrated that two most active compounds inhibited tubulin polymerization. Computational analysis confirmed the suitability of the employed benzimidazole-acrylonitrile skeleton for the binding within the colchicine binding site in tubulin, thus rationalizing the observed antitumor activities, and demonstrated that E-isomers are active substances. It also provided structural determinants affecting both the binding position and the matching affinities, identifying the attached NMe₂ group as the most dominant in promoting the binding, which allows ligands to optimize favourable cation∙∙∙π and hydrogen bonding interactions with Lys352.