A [2,3]-Wittig rearrangement approach towards the stereoselective synthesis of the C(10)–C(20) backbone of the fumonisins

Fusarium verticillioides (= Fusarium moniliforme) a common fungal contaminant of maize throughout the world has been associated with diseases in both man and animals. The structure of the fumonisins, a family of structurally related mycotoxins isolated from cultures associated with the high incidence of human oesophageal cancer in the Transkei region in South Africa and with equine leucoencephalomalacia, a neurological disorder in horses and donkeys, has been established. The main mycotoxin, fumonisin B1 consists of the diester formed by the C(14) and C(15) hydroxyl groups of (2S,3S,5R,10R,12S,14S,15R,16R)-2- amino-12,16-dimethyleicosane-3,10,14,15-pentaol with the Si carboxy group of propane- 1,2,3-tricarboxylic acid. A comparison of the structures of the 28 known fumonisins reveals that they share a common structural motif for the C(11)-C(20) unit, and probably also the same stereochemistry for the 4 stereogenic centres present in this unit. Disconnection of the C(9)–C(10) bond in a retrosynthetic analysis of the fumonisins C20 backbone (C19 in the fumonisin C series)identifies (3S,5S,6R,7R)-3,7-dimethylundecane-1,5,6-triol as a common building block for the synthesis of any of the fumonisins. In the dissertation the retrosynthetic analysis of this 3,7-dimethylundecane-1,5,6-triol building block identifies (3S,4R,5R)-5-methylnonane-1,3,4-triol as a viable target which in turn could be derived from a simple starting material trans-4-hexen-3-one. Key reactions identified to realise the required transformations leading to the identified target included kinetic enzymatic resolution of the racemic alcohol obtained from trans-4-hexen-3-one, and a pivotal role for both the [2,3]-Wittig rearrangement and the use of Sharpless asymmetric epoxidation methodology as these reactions generated the requisite stereogenic centres present in (3S,4R,5R)-5-methylnonane-3,4-diol. In this manner a synthetic route from trans-4-hexen-3- one to (2R,3R,4R,5R,6E)-4-(benzyloxy)-2,3-epoxy-5-methylnon-6-en-1-ol using appropriate functional group transformations and protective group strategies, with complete stereochemical control, were developed in this work. Alternative strategies to overcome problems encountered during the synthesis are presented for future work. The conversion of the 4-(benzyloxy)-2,3-epoxy-5-methylnon-6-en-1-ol intermediate to the protected 5- methylnonane-1,3,4-triol target could not be carried out due to time constraints and material shortages.Dissertation (MSc)--University of Pretoria, 2011.Chemistryunrestricte

Organic-inorganic hybrid materials from metal halides

The materials we study combine organic components and metal halides, leading to the formation of organic-inorganic hybrid materials. These materials retain and combine the desired inherent properties of both constitutional moieties, rendering them multifunctional. The effects of change in variables on the structural trends in the crystal systems were investigated. Characterisation was done employing single crystal and powder X-ray diffraction.http://www.satnt.ac.zaam201

Structures and trends of one-dimensional halide-bridged polymers of five-coordinate cadmium(II) and mercury(II) with benzopyridine and -pyrazine-type N-donor ligands

Cadmium and mercury dihalides were reacted with benzopyridine- and benzopyrazine-type N-donor ligands as Lewis bases. The solid-state structures of 13 novel reaction products were studied by X-ray diffraction. Eleven of the structures can be classified as one-dimensional halide-bridged polymers of composition [MIJμ-X)2IJL)]∞, in which the metal ion displays a coordination number of five, while the remaining two structures exhibit one-dimensional dimers that are linked by long, semi-coordinate M– X⋯M–X interactions to form pseudo-halide-bridged polymers. Four of the structures contain Cd2+ as the metal ion, while the remaining nine have Hg2+ as the metal ion. Although all the halide-bridged polymers show a coordination number of five, two different metal cation geometries are displayed. A detailed comparison of all structural results, which includes related compounds from the literature and allows for the study of the effect of an increase in the width of the N-donor ligand on the halide-bridged chain geometries and other structural features, concludes the discussion.CS gratefully acknowledges the National Research Foundation for financial support through an Innovation Scholarship (SFH20100706000011827). MR acknowledges financial support from the University of Pretoria and the National Research Foundation (Grant No. 87659).http://www.rsc.org/crystengcomm2016-10-19am201

Structures and trends of neutral MXxsolvent4−x tetrahedra and anionic [MX4]2− tetrahalometallates of zinc(II), cadmium(II) and mercury(II) with benzopyridine- and benzopyrazine-type N-donor ligands or cations

Zinc, cadmium and mercury dihalides were reacted with benzopyridine- and benzopyrazinetype N-donor molecules acridine (acr), phenazine (phe), quinoline (quin) and quinoxaline (quinox) as ligands or cations. The solid-state structures of 16 novel, zero-dimensional reaction products were studied by X-ray diffraction. Seven of the compounds were prepared in the presence of an inorganic acid, HX, which resulted in the formation of anionic tetrahalometallates, [MX4]2−, with either Cd2+ or Hg2+ as the cationic metal center and quinolinium (quin-H), quinoxalinium (quinox-H), acridinium (acr-H) or phenazinium (phe- H) as the counter cation. The other nine compounds contain Zn2+ as the tetrahedral cationic node. Five of the nine Zn2+ compounds are neutral, and four are ionic. Three of the four ionic Zn2+ compounds contain an anionic tetrahalometallate inorganic moiety, [ZnX4]2−, while the inorganic component of the fourth ionic Zn2+ compound is coordinated by three halido ligands and one aqua ligand, [ZnX3(H2O)]−. Structural trends, hydrogen bonding interactions and aromatic interactions are identified. In addition, it is observed that in the case of the neutral phenazine or acridine compounds, the size of the organic molecule prevents coordination of the molecule to the metal ion.National Research Foundation financial support through an Innovation Scholarship (SFH20100706000011827). University of Pretoria and the National Research Foundation (Grant No. 87659).http://www.rsc.org/journals-books-databases/about-journals/crystengcomm2017-04-30hb2016Chemistr

Organies-anorganiese hibriedverbindings van metaalhaliede

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The MX₂L_x matrices, with M = Zn²⁺, Cd²⁺, Hg²⁺, X = Cl⁻, Br⁻, I⁻ and L = pyrazine, quinoxaline, phenazine

<p>Three structures combining the ditopic organic ligand quinoxaline with divalent metal halides MX₂, with M = Cd²⁺ and Hg²⁺, are reported. All three structures are coordination polymers, with the quinoxaline ligand acting as organic linker between metal centers. In two structures, with M = Hg²⁺ and X = Cl⁻ or Br⁻, the formation of a 1-D, halide-bridged polymer in addition to the quinoxaline coordination polymer increases the dimensionality of the structure to 2-D, while in the case of M = Hg²⁺ and X = Cl⁻, the formation of two halide-bridged polymers along with the coordination polymer results in the creation of a 3-D structure. Structural trends are identified, and the templating effect of the organic ligand is highlighted, through horizontal and vertical comparisons of these structures with related structures reported in the literature obtained upon combining the said metal halides with the related organic ligands pyrazine, quinoxaline, and phenazine, presented as the resulting matrices of structures.</p

Structure determination of fatty acid ester biofuels via in situ cryocrystallisation and single crystal X-ray diffraction

Please read abstract in the article.The Claude Leon Foundation and NRF Green Economy Fund (Grant UID: 98053) for financial assistance. They would also like to acknowledge the NRF (Grant UID: 78572) for the purchase of the D8 VENTURE and OHCD device.http://www.rsc.org/journals-books-databases/about-journals/crystengcomm2020-01-07hj2019Chemistr