Antifungal copyrine alkaloids: crystal structure of 3-methylsampangine

3-Methylsampangine, C₁₆H₁₀N₂O, crystallizes in the monoclinic space group P2₁/c witha=7.260(3),b=10.697(5),c=15.342(6) Å, and =102.69(4). All nonhydrogen atoms of this potent antifungal agent are planar to within 0.082 Å. The title compound exhibits potentin vitro antifungal activity againstC. neoformans, C. albicans andA. fumigatus.     

The use of proton transfer reaction mass spectrometry for high throughput screening of terpene synthases

In this work, we introduce the application of proton transfer reaction mass spectrometry (PTR-MS) for the selection of improved terpene synthase mutants. In comparison with gas chromatography mass spectrometry (GC-MS)-based methods, PTR-MS could offer advantages by reduction of sample preparation steps and analysis time. The method we propose here allows for minimal sample preparation and analysis time and provides a promising platform for the high throughput screening (HTS) of large enzyme mutant libraries. To investigate the feasibility of a PTR-MS-based screening method, we employed a small library of Callitropsis nootkatensis valencene synthase (CnVS) mutants. Bacterial cultures expressing enzyme mutants were subjected to different growth formats, and headspace terpenes concentrations measured by PTR-Qi-ToF-MS were compared with GC-MS, to rank the activity of the enzyme mutants. For all cultivation formats, including 96 deep well plates, PTR-Qi-ToF-MS resulted in the same ranking of the enzyme variants, compared with the canonical format using 100 mL flasks and GC-MS analysis. This study provides a first basis for the application of rapid PTR-Qi-ToF-MS detection, in combination with multi-well formats, in HTS screening methods for the selection of highly productive terpene synthases.     

Synthesis and evaluation of caged Garcinia xanthones

Inspired by the combination of unique structure and potent bioactivities exhibited by several family members of the caged Garcinia xanthones, we developed a synthesis of simplified analogues that maintain the overall caged motif. The caged structure of these compounds was constructed via a site-selective Claisen/Diels-Alder reaction cascade. We found that the fully substituted caged structure, in which are included the C18 and C23 geminal methyl groups, is necessary to maintain bioactivity. Analogue had comparable activity to the natural products of this family, such as gambogic acid. These compounds exhibit cytotoxicity in a variety of tumor cell lines at low micromolar concentrations and were found to induce apoptosis in HUVE cells. In addition, studies with HL-60 and HL-60/ADR cells indicate that these compounds are not affected by the mechanisms of multidrug resistance, conferred by P glycoprotein expression, typical of relapsed cancers and thus represent a new and potent pharmacophore.     

Hyperkähler structures and infinite-dimensional Grassmannians

In this paper, we describe an example of a hyperkähler quotient of a Banach manifold by a Banach Lie group. Although the initial manifold is not diffeomorphic to a Hilbert manifold (not even to a manifold modelled on a reflexive Banach space), the quotient space obtained is a Hilbert manifold, which can be furthermore identified either with the cotangent space of a connected component (j∈Z), of the restricted Grassmannian or with a natural complexification of this connected component, thus proving that these two manifolds are isomorphic hyperkähler manifolds. Moreover, Kähler potentials associated with the natural complex structure of the cotangent space of and with the natural complex structure of the complexification of are computed using Kostant-Souriau's theory of prequantization.     

Mimicking biological cation-transport based on sphere-surface supramolecular chemistry: simultaneous interaction of porous capsules with molecular plugs and passing cations

Spherical capsules of the type [{(Mo)Mo(5)}(12){Mo(2)(ligand)}(30)](n-) exhibiting 20 {Mo(9)O(9)} pores with crown ether functions allowed us to perform a sophisticated study of the title phenomenon based on synthetic work as well as NMR spectroscopy. The pores of the host system interact in solution specifically with guests that can be noncovalently bonded, such as formamidinium and acetamidinium cations, while having different affinities to the pores. The exchange between the guest species present in solution and in the pores was investigated, including, besides the extreme scenarios of complete pore closing and complete opening, that of stepwise pore plugging. Because of this option it was possible to model for the first time passive transmembrane cation transport based on gated pores/channels. These have the appropriate dimensions and can even adopt different structure flexibilities in response to different cations. The present investigation is based on related syntheses as well as on numerous detailed (7)Li NMR studies of Li(+) transport/exchange equilibria in dependence of the pore environment/guest situations. One compound containing capsules with sulfate ligands (2) could be obtained in which all the pores are plugged with formamidinium cations and another corresponding one was obtained with additionally encapsulated Ca(2+) ions (3); these were taken up after temporary release of some of the formamidinium plugs/guests upon short heating of the related solution.     

Photoelectron spectroscopy and electronic structure calculations of d1 vanadocene compounds with chelated dithiolate ligands: implications for pyranopterin Mo/W enzymes

Gas-phase photoelectron spectroscopy and density functional theory have been used to investigate the electronic structures of open-shell bent vanadocene compounds with chelating dithiolate ligands, which are minimum molecular models of the active sites of pyranopterin Mo/W enzymes. The compounds Cp2V(dithiolate) [where dithiolate is 1,2-ethenedithiolate (S2C2H2) or 1,2-benzenedithiolate (bdt), and Cp is cyclopentadienyl] provide access to a 17-electron, d1 electron configuration at the metal center. Comparison with previously studied Cp2M(dithiolate) complexes, where M is Ti and Mo (respectively d0 and d2 electron configurations), allows evaluation of d0, d1, and d2 electronic configurations of the metal center that are analogues for the metal oxidation states present throughout the catalytic cycle of these enzymes. A "dithiolate-folding effect" that involves an interaction between the vanadium d orbitals and sulfur p orbitals is shown to stabilize the d1 metal center, allowing the d1 electron configuration and geometry to act as a low-energy electron pathway intermediate between the d0 and d2 electron configurations of the enzyme.     

Structurally different divalent metallasiloxanes [Mg{O(Ph2SiO)2}2]-μ-(LiPy)-μ-{(LiPy)3(OH)(Cl)}], [Cr{O(Ph2SiO)2}-μ-(LiPy2)2], and [{O(Ph2SiO)2}Co{O(Ph2SiO)3)}-μ-(LiPy2)2] from Ph2Si(OH)2/2BuLi and the metal dichlorides

Three structurally different metallasiloxanes were formed from reactions between in situ generated suspensions of Ph₂Si(OH)₂/BuLi (1∶2) in tetrahydrofuran (THF) with, metal dichlorides MgCl₂·2THF, CrCl₂, or CoCl₂ followed by toluene/Py (Py=pyridine) work-up. The X-ray structures are reported for: [Mg{O(Ph₂SiO)₂}₂]-μ-(LiPy)-μ-{(LiPy)₃(OH)(Cl)] (1) incorporating two six-membered magnesiasiloxane rings and an MgLi₃O₃Cl cubane fragment, [{O(Ph₂SiO)₂}Co{O(Ph₂SiO)₃}-μ-(LiPy₂)₂] (2) with both six-and eight-membered cobaltasiloxane rings and [Cr{O(Ph₂SiO)₂}₂-μ-(LiPy₂)₂] (3) with two six-membered chromiasiloxane rings. Structure assembly in these cases is apparently dictated by the metal dichloride. The compound [{O(Ph₂SiO)₂}Mg{O(Ph₂SiO)₃}-μ-(CoClPy)₂]·Py (4) is formed from [{O(Ph₂SiO)₂}Mg{O(Ph₂SiO)₃}-μ-(LiPy₂)₂] and CoCl₂ (1∶2).     

Surface modification of activated polymeric matrices by dendritic attachments

Aware of the growing interest in materials that exhibit specific physiochemical properties and potential applications, we focused our work on modifying commercial agarose with polyfunctional dendrons capable of molecular recognition through hydrogen bonding. 2,6‐Di(acylamino)pyridine moieties within the internal superstructure of dendritic macromolecules have been reported to be capable of forming H‐bonded complexes with imide groups, such as barbituric acid and its derivatives. We report the synthesis of new dendrons possessing multiple 2,6‐di(acylamino)pyridinyl sites, each capable of molecular recognition, and the development of new polymeric supports of an activated agarose matrix by surface modification. From comparative studies of the beads modified by different dendrons, we found improved results in those dendritic supports possessing 2,6‐di(acylamino)pyridinyl moieties, except when their juxtaposition between the groups promoted inner H bonds. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2779–2786, 2000