Purification and Characterization of an Active Principle, Lawsone, Responsible for the Plasmid Curing Activity of Plumbago zeylanica Root Extracts

Plasmid curing is the process of obviating the plasmid encoded functions such as antibiotic resistance, virulence, degradation of aromatic compounds, etc. in bacteria. Several plasmid curing agents have been reported in literature, however, no plasmid curing agent can eliminate all plasmids from different hosts. Hence, there is always a need for novel plasmid curing agents that can be effectively used for reversal of plasmid encoded functions such as virulence, antibiotic resistance, etc. In the present study, an active principle responsible for the plasmid curing activity was purified from roots of Plumbago zeylanica by bioassay guided fractionation and identified as 2-hydroxy-1,4-naphthoquinone (lawsone), on the basis of spectral and analytical data such as NMR, GCMS, FTIR. Plasmid curing activity of lawsone was observed against reference as well as wild plasmids (pBR322, pRK2013, R136, pUPI281, and pUPI282) residing in a range of hosts. Curing of plasmid was confirmed by agarose gel electrophoresis. MICs of antibiotics against A. baumannii A24 (pUPI281) and E. coli (pRK2013) decreased significantly in presence of lawsone suggesting synergy between lawsone and antibiotics. Lawsone also inhibited transfer of plasmid pRK2013 to E. coli either by transformation or conjugation. Viability assays (MTT) revealed that lawsone was not toxic to mammalian cells. Thus, the present investigation has revealed lawsone as an effective plasmid curing agent capable of suppressing development and spread of antibiotic resistance. Further, lawsone has important application in basic research to identify phenotypes encoded by the plasmids in plasmid curing experiments. To the best of our knowledge this is the first report of plasmid curing activity of lawsone isolated from roots of P. zeylanica

Using Magnetic Levitation to Separate Mixtures of Crystal Polymorphs

Magnetische Levitation (MagLev) ist eine einfache Trennmethode für Kristallpolymorphe mit Dichteunterschieden (Δρ) von nur 0.001 g cm−3. Für vier organische Verbindungen wurden dichtebasierte Trennungen verschiedener kristalliner Formen gezeigt: 5-Methyl-2-[(2-nitrophenyl)amino]-3-thiophencarbonitril, Sulfathiazol, Carbamazepin und trans-Zimtsäure.Chemistry and Chemical Biolog

Randomized Clinical Trial of High-Dose Rifampicin With or Without Levofloxacin Versus Standard of Care for Pediatric Tuberculous Meningitis: The TBM-KIDS Trial

Background. Pediatric tuberculous meningitis (TBM) commonly causes death or disability. In adults, high-dose rifampicin may reduce mortality. The role of fluoroquinolones remains unclear. There have been no antimicrobial treatment trials for pediatric TBM. Methods. TBM-KIDS was a phase 2 open-label randomized trial among children with TBM in India and Malawi. Participants received isoniazid and pyrazinamide plus: (i) high-dose rifampicin (30 mg/kg) and ethambutol (R30HZE, arm 1); (ii) high-dose rifampicin and levofloxacin (R30HZL, arm 2); or (iii) standard-dose rifampicin and ethambutol (R15HZE, arm 3) for 8 weeks, followed by 10 months of standard treatment. Functional and neurocognitive outcomes were measured longitudinally using Modified Rankin Scale (MRS) and Mullen Scales of Early Learning (MSEL). Results. Of 2487 children prescreened, 79 were screened and 37 enrolled. Median age was 72 months; 49%, 43%, and 8% had stage I, II, and III disease, respectively. Grade 3 or higher adverse events occurred in 58%, 55%, and 36% of children in arms 1, 2, and 3, with 1 death (arm 1) and 6 early treatment discontinuations (4 in arm 1, 1 each in arms 2 and 3). By week 8, all children recovered to MRS score of 0 or 1. Average MSEL scores were significantly better in arm 1 than arm 3 in fine motor, receptive language, and expressive language domains (P < .01). Conclusions. In a pediatric TBM trial, functional outcomes were excellent overall. The trend toward higher frequency of adverse events but better neurocognitive outcomes in children receiving high-dose rifampicin requires confirmation in a larger trial. Clinical Trials Registration. NCT02958709

From supramolecular selectivity to nanocapsules

Doctor of PhilosophyDepartment of ChemistryChrister B. AakeroyA family of three 2-aminopyrazine derivatives were prepared and co-crystallized with thirty carboxylic acids. Our theoretical charge calculations and experimental results from 90 reactions demonstrated that decreasing the charge on the hydrogen-bond acceptor sites results in a decrease of the supramolecular yield (the frequency of occurrence of the desired outcome). However, synthon crossover (undesired connectivity) was observed 7/12 times and was unavoidable due to competitive binding sites present in the N-heterocyclic bases chosen. To avoid synthon crossover, we used a strategy based on geometric bias. We utilized hydrogen-bonding two-point contacts and halogen-bonding single-point contacts for supramolecular reactions with the 2-aminopyrazine family of compounds. The desired two-point contact and single-point contact (N•••I or N•••Br) appeared in 9/9 times even in the presence of other potentially interfering intermolecular interactions. In addition, the role of charge in controlling the presence/absence of proton transfer was also highlighted. To establish a hierarchy in halogen-bonding interactions we designed and synthesized a library of eight molecules equipped with two different halogen bond donors and combined with variety of halogen-bond acceptors. 11 Halogen-bonded co-crystals were obtained; however, positional disorder of I/Br atoms obscures a complete analysis. This problem was solved by introducing asymmetry in the halogen-bond donor molecules. Finally, successfully demonstrated an unprecedented hierarchy in halogen-bond interactions based on electrostatics. We developed high-yielding Suzuki-Miyaura coupling reactions of tetraboronic pinacolyl ester cavitand to iodoarenes with a range of functional groups (electron withdrawing/donating group and a heterocycle) that show robustness and versatility, making it a ‘launch pad’ for the synthesis of many new cavitands in a facile manner. We have also successfully demonstrated cavitand functionalization from tetraaldehyde to tetraoximes using ‘solvent assisted grinding’, irrespective of the position of the aldehyde. Finally, we prepared tetra-substituted pyridyl and carboxylic acid cavitands having an ellipsoidal cavity capable of encapsulating asymmetric guest molecules and was subsequently obtained the first of its kind, C[subscript]2v symmetric molecular capsule with encapsulated asymmetric guest molecule

Avoiding “Synthon Crossover” in Crystal Engineering with Halogen Bonds and Hydrogen Bonds

A combination of halogen bonds and hydrogen bonds has been used for effective assembly of three co-crystals containing desired one-dimensional architectures where the interactions within each assembly can be modulated using tunable electrostatics. The central tecton in these structures, 2-aminopyrazine, can interact with suitable hydrogen-bond donors and halogen-bond donors simultaneously without any “synthon crossover”. When different 2-aminopyrazine-based molecules are co-crystallized with 1,4-diiodo-tetrafluorobenzene (DITFB), a N···I halogen bond is driving the co-crystal synthesis in each case, whereas the N–H···N/N···H–N homosynthon is responsible for creating infinite chains of alternating pyrazine and DITFB molecules in the three crystal structures. The importance of electrostatic and geometric complementarity for refining strategies for supramolecular synthesis is emphasized

Establishing a Hierarchy of Halogen Bonding by Engineering Crystals without Disorder

It has been shown, using a foundation of new structural data, that the relative strength and capability of iodo- and bromo-based molecules to act as halogen-bond donors in a competitive supramolecular arena accurately reflect a ranking of halogen-bond donors based upon electrostatic molecular potentials. Furthermore, to obtain the critical structural information, a protocol (comprising a lowering of molecular symmetry and the addition of strong and directional hydrogen bonds) for engineering crystals without positional disorder was successfully developed

Structural Chemistry of Oximes

Oximes (RR′CN–OH) represent an important class of organic compounds with a wide range of practical applications, but a systematic examination of the structural chemistry of such compounds has so far not been carried out. Herein, we report a systematic analysis of intermolecular homomeric oxime···oxime interactions, and identify hydrogen-bond patterns for four major categories of oximes (R′ = −H, −CH₃, −NH₂, −CN), based on all available structural data in the CSD, complemented by six new relevant crystal structures. The structural behavior of oximes examined here, can be divided into four groups depending on which type of predominant oxime···oxime interactions they present in the solid-state: (i) O–H···N dimers (R₂²(6)), (ii) O–H···N catemers (C(3)), (iii) O–H···O catemers (C(2)), and (iv) oximes in which the R′ group accepts a hydrogen bond from the oxime moiety catemers (C(6)). The electronic and structural effects of the substituent (R′) on the resulting assembly has been explored in detail to rationalize the connection between molecular structure and supramolecular assembly

Competing hydrogen-bond and halogen-bond donors in crystal engineering

In order to study the structure-directing competition between hydrogen- and alogen-bond donors we have synthesized two ligands, 3,3’-azobipyridine and 4,4’-azobipyridine, and co-crystallized them with a series of bi-functional donor molecules comprising an activated halogen-bond donor (I or Br) as well as a hydrogen-bond donor (acid, phenol or oxime) on the same backbone. Based on the subsequent single-crystal analysis, 5 of 6 co-crystals of 3,3’-azobipyridine are assembled using hydrogen bonds as the primary driving force accompanied by weaker secondary (C-X...O) interactions. However, in 5 out of the 6 co-crystals of 4,4’-azobipyridine, both hydrogen bonds (O-H...N) and halogen bonds (C-X...N) are present as structure-directing interactions leading to 1-D chains. Since the charges on the acceptor sites in 3,3’-and 4,4’-azobipyridine are very similar, the observed difference in binding behaviour highlights the importance of binding-site location on the acceptor molecules (anti-parallel in 3,3’-azobipyridine and co-linear in 4,4’-azobipyridine) as a direct influence over the structural balance between hydrogen- and halogen-bond donors

Structure and thermodynamics of a multimeric cavitand assembly

A set of COOH···N(pyridine) 5 hydrogen bonds have been utilized in the targeted synthesis of a cavitand-based assembly. A cavitand appended with four pyridyl groups was synthesized from a Suzuki coupling of a tetrabromocavitand and 3-pyridyl boronic acid. The product resulting from the reaction between the tetra-pyridyl cavitand and 4-nitrobenzoic acid was investigated in solution using isothermal titration calorimetry (ITC) under equilibrium conditions, and in the solid state through single-crystal X-ray diffraction and infrared spectroscopy. The results show that the targeted pentameric hydrogen-bonded architecture was isolated in the solid-state, and the infrared spectroscopy confirm the presence of COOH···N(py) interactions. The same assembly, with a 1:4 cavitand:acid stoichiometry, is also present in solution in acetonitrile and the enthalpy of binding for this reaction is approximately -45 kJ/mol

Structural chemistry of oximes

Oximes (RR'C=N-OH) represent an important class of organic compounds with a wide range of practical applications, but a systematic examination of the structural chemistry of such compounds has so far not been carried out. Herein, we report a systematic analysis of intermolecular homomeric oxime•••oxime interactions, and identify hydrogen-bond patterns for four major categories of oximes (R' = -H, -CH[subscript 3], -NH[subscript 2], -CN), based on all available structural data in the CSD, complemented by six new relevant crystal structures. The structural behavior of oximes examined here, can be divided into four groups depending on which type of predominant oxime•••oxime interactions they present in the solid-state; (i) O-H•••N dimers (R[superscript 2][subscript 2](6)), (ii) O-H•••N catemers (C(3)), (iii) O-H•••O catemers (C(2)), and (iv) oximes in which the R' group accepts a hydrogen bond from the oxime moiety catemers (C(6)). The electronic and structural effects of the substituent (R') on the resulting assembly has been explored in detail in order to rationalize the connection between molecular structure and supramolecular assembly