Studies towards the biomimetic synthesis of bisesquiterpene lactones

A possible biomimetic connection between atractylolide, hydroxyatractylolide and biatractylolide and biepiasterolide has been demonstrated by efficiently generating the biatractylolide and biepiasterolide core structures from atractylolide and hydroxyatractylolide model butenolides via a radicaloid intermediate in a single step in good yield.     

ILP approaches to the blockmodel problem

Blockmodelling is a method for identifying structural similarities or equivalences between elements which has applications in a variety of contexts, including multiattribute performance assessment. One criterion for forming blocks results in a difficult non-linear integer programme. We give several integer linear programming formulations of this problem and provide comparative computational results. We show that methods of reducing symmetry proposed by Sherali and Smith are not effective in this case and propose an iterative approach in which the size of the problem is reduced.     

Reaction of a phosphaketene with diiron enneacarbonyl: Possible intermediacy of a terminal phosphinidene complex

Evidence is presented for the intermediacy of a terminal phosphinidene complex, [2,4,6-(t-Bu)₃C₆H₂]PFe(CO)₄, in the reaction of [2,4,6-(t-Bu)₃C₆H₂]PCO with Fe₂(CO)₉.     

Analysis of supramolecular interactions in alendroniate alkali metal salts: synthesis,structure, and properties of novel sodium alendronate polymorph

A new polymorph of anhydrous sodium alendronate, C₄H₁₂NO₇P₂Na, has been synthesized and characterized by single crystal X-ray diffraction as well as infrared spectroscopy and thermal analysis. The title compound crystallizes in the monoclinic P2₁/c space group. Asymmetric unit consists of one alendronic anion and one sodium cation. An interplay of classical strong O-H^…O, N-H^…O and non-classical weak C-H^…O hydrogen bonds creates 3D framework in the crystal. Contrary to previously reported sodium alendronate salts, in which Na⁺ cation is surrounded by six-coordinated sphere, in compound (1), the Na⁺ cation is five-coordinated in a distorted trigonal-bipyramidal geometry. In order to provide a detailed investigation of the molecular arrangement in view of intermolecular interactions, the title compound was compared with alendronic acid and other known alkali metal alendronate salts, retrieved from the Cambridge Crystal Structure Database. The intercontacts were qualitatively and quantitatively compared using Hirshfeld surface analysis. It highlights that strong O^…H/H^…O and subtle H^…H contacts play an influential role in the total surface area. The Me^+…H/H^…Me⁺ and Me^+…O/O^…Me⁺ contacts are meaningful as well. These evidently simple systems show a diverse complexity. Moreover, the powder X-ray diffraction, DSC, thermogravimetry/derivative thermogravimetry, and FT-IR results are also reported.

     

Spontaneous generation of stable pnictinyl radicals from "jack-in-the-box" dipnictines: a solid-state, gas-phase, and theoretical investigation of the origins of steric stabilization

The molecular structures of the stable phosphinyl and arsinyl radicals, .PnR(2) [Pn = P (2); As (4); R = CH(SiMe(3))(2)], have been determined by gas-phase electron diffraction (GED) in conjunction with ab initio molecular orbital calculations. The X-ray crystal structures of the corresponding dipnictines, the "dimers", R(2)PnPnR(2) [Pn = P (1), As (3)], and the chloro derivatives R(2)PnCl [Pn = P (5), As (6)] have also been determined. Collectively, these structural investigations demonstrate that large distortions of the ligands attached to Pn occur when the pnictinyl radicals unite to form the corresponding dipnictine dimers. Principally, it is the shape and flexibility of the CH(SiMe(3))(2) ligands that permit the formation of the P-P and As-As bonds in 1and 3, respectively. However, theoretical studies indicate that in the process of pnictinyl radical dimerization to form 1 and 3, both molecules accumulate substantial amounts of potential energy and are thus primed to spring apart upon release from the solid state by melting, dissolution, or evaporation. The insights gleaned from these unusual systems have permitted a deeper understanding of the functioning of sterically demanding substituents.