Total synthesis of (+)-zaragozic acid C

A total synthesis of (+)-zaragozic acid C is described. Key features of the synthesis are the use of a double Sharpless asymmetric dihydroxylation reaction of diene 6 to control stereochemistry at four contiguous stereocenters from C3 to C6; the introduction of the C1-side chain by reaction between the anion derived from the dithiane monosulfoxide 27 and the core aldehyde 12; a high yielding, acid-mediated simultaneous acetonide deprotection-dithiane removal-ketalization procedure leading exclusively to the 2, 8-dioxabicyclo[3.2.1]octane core 34; and a novel triple oxidation procedure allowing installation of the tricarboxylic acid.     

“Living” radical graft polymerization of styrene to styrene butadiene rubber (SBR) with 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO)

Well‐defined graft copolymers with styrene butadiene rubber (SBR) backbones and polystyrene branches were synthesized by living free radical polymerization (LFRP) techniques. Thus 1‐ benzoyl‐2‐phenyl‐2‐(2′,2′,6′,6′‐tetramethyl‐piperidinyl‐1′‐oxy)ethane (BZ‐TEMPO) was synthesized and hydrolyzed to the corresponding 1‐hydroxyl derivative. This functional nitroxyl compound was coupled with brominated SBR (SBR‐Br). The resulting macroinitiator (SBR‐TEMPO) for “living” free radical polymerization was then heated in the presence of styrene for the formation of the controlled graft copolymer. ¹H‐NMR and IR spectroscopy were used to investigate the structure of the polymers. Copyright © 2004 John Wiley & Sons, Ltd.     

Spectrophotometric determination of hydrazines withperi-naphthindan-2,3,4-trione hydrate

Summary A new micromethod for spectrophotometric determination of hydrazine compounds is described. It is based on a reaction withperi-naphthindan-2,3,4-trione hydrate at pH 2.5 to give a red precipitate of dihydroxy-peri-naphthindenone which is dissolved in methanol and measured at 460 nm. The results obtained show an average recovery of 99.8 %, the precision being ± 1 %.

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Zusammenfassung Eine neue Mikromethode zur spektrophotometrischen Bestimmung von Hydrazinverbindungen wurde beschrieben. Sie beruht auf der Reaktion mit peri-Naphthindan-2,3,4-trion-hydrat bei pH 2,5, wobei ein roter Niederschlag von Dihydroxy-peri-naphthindenon entsteht, der in Methanol gelöst und bei 460 nm gemessen wird. 99,8% Substanz werden wiedergefunden, die Genauigkeit beträgt ±1%.

     

Effect of gamma-rays on the formation of color centers in copper-containing lead borate glasses

Absorption bands in the range of 350–950 nm, induced in copper-containing lead borate glasses by -rays were identified and characterized. The effect of irradiation dose, copper oxide and lead oxide contents on the intensity and position of the induced absorption bands were also considered. Several induced absorption bands were observed. At least two bands in the ranges of 740–780 and 850–870 nm could be identified. They are suggested to be associated with induced Cu⁽²⁺⁾ ions. The band in the 800–830 nm (1.6 eV) range is ascribed to the Pb⁽³⁺⁾ ion, whereas others in the ranges of 600–630 and 650–730 nm are associated with the intrinsic defects formed in the base glass.     

Graft polymerization of vinyl monomers onto cellulose in presence of soda lime glass. I

Sodium bisulfite–soda lime glass has proved to be a good initiator for polymerization and graft polymerization onto cellulose of some vinyl monomers. A scheme dealing with the mechanism of initiation has been proposed assuming trapping of the bisulfite radical inside the glass frame-work to form a so-called sulfur-impregnated solid. Such a solid has paramagnetic properties and acts on the vinyl monomers and cellulose as any free-radical-producing source thus leading to polymerization and graft polymerization onto cellulose. Other radicals containing sulfur, such as sulfite, sulfate, and persulfate failed to give such property with soda lime glass. With the sodium bisulfite–soda lime glass system the reactivity decreases in the order methyl methacrylate > ethyl acrylate > acrylonitrile which is inconsistent with the arrangement of acceptor monomers with decreasing electron-donating ability. This may reflect interference of the addition reaction which may take place between the monomer and bisulfite and the rate of which may depend on the activation energy of the monomer.     

New pyranosyl cembranoid diterpenes from Sarcophyton trocheliophorum

During our continual searching programme for novel bioactive metabolites from Sarcophyton trocheliophorum, collected from Red Sea, we describe herein the isolation and structural elucidation of further two new pyrane-based cembranoid diterpenes: 9-hydroxy-7,8-dehydro-sarcotrocheliol (1) and 8,9-expoy-sarcotrocheliol acetate (2), along with the well-known sarcotrocheliol acetate (3), (+)-sarcophine (4), (+)-sarcophytoxide (5) and (-)-sarcophytoxide (6). The chemical structures of compounds 1 and 2 were determined on the basis of 1D and 2D NMR (¹H, ¹³C, ¹H–¹H COSY, HMQC, HMBC and NOE), mass spectra (ESI and HR-ESIMS) and by comparison with related structures. The antimicrobial activities of the reported compounds 1–6 were investigated. According to the molecular docking study of compounds 1–6 using 3D structure of α,β tubulin in complex with taxol (PDB code 1JFF) and epothilone A (PDB code 1TVK), sarcophine (4) displayed the highest affinity towards both crystal structures, followed by 5 and 6, meanwhile pyrane-based cembranoid diterpenes (1–3) showed less affinity.     

Chemoselective thioacetalization and transthioacetalization of carbonyl compounds catalyzed by immobilized scandium(III) triflate in ionic liquids

Immobilized scandium triflate [Sc(OTf)₃] in ionic liquids has been found to be an extremely efficient and recyclable catalyst for the thioacetalization and transthioacetalization of both aromatic and aliphatic aldehydes. Significant rate acceleration and chemoselectivity was achieved by employing this catalytic system.     

A novel and expeditious approach to unusual spirolactam building blocks

A rapid access to 7-azaspiro[4.5]decan-6-ones 1 involving three regio- and chemoselective reactions starting from tetrabromonorbornyl derivatives is described. The alkaline H(2)O(2) cleavage reaction of monosubstituted alpha-diketones 9 furnished the potential bridged bicyclic lactones 10in a highly regio- and stereoselective manner. The radical-mediated, intermolecular bridgehead C-C bond formation of the versatile bridged lactones 10 with acrylonitrile followed by LAH reduction of the adduct 13 intriguingly leads to the formation of novel spirolactam building blocks 1.     

Synthesis and Reactions of 5-Amino-3-(3-methyl-5-oxo-1-phenyl-2-pyrazolin-4-yl)-7-phenyl-7 H -thiazolo[3,2- a ]pyrimidine-6-carbonitrile

5-Amino-3-(3-methyl-5-oxo-1-phenyl-2-pyrazolin-4-yl)-7-phenyl-7H-thiazolo[3,2-a]pyrimidine-6-carbonitrile was synthesized via the reaction of 4-(2-aminothiazol-4-yl)-3-methyl-1-phenyl-2-pyrazolin-5-one with benzylidene malononitrile and was then transformed to related fused heterocyclic systems. The antifungal and antibacterial studies revealed in some cases excellent biocidal properties.     

Determining molecular structures and conformations directly from electron diffraction using a genetic algorithm.

A global optimization strategy, based upon application of a genetic algorithm (GA), is demonstrated as an approach for determining the structures of molecules possessing significant conformational flexibility directly from gas-phase electron diffraction data. In contrast to the common approach to molecular structure determination, based on trial-and-error assessment of structures available from quantum chemical calculations, the GA approach described here does not require expensive quantum mechanical calculations or manual searching of the potential energy surface of the sample molecule, relying instead upon simple comparison between the experimental and calculated diffraction pattern derived from a proposed trial molecular structure. Structures as complex as all-trans retinal and p-coumaric acid, both important chromophores in photosensing processes, may be determined by this approach. In the examples presented here, we find that the GA approach can determine the correct conformation of a flexible molecule described by 11 independent torsion angles. We also demonstrate applications to samples comprising a mixture of two distinct molecular conformations. With these results we conclude that applications of this approach are very promising in elucidating the structures of large molecules directly from electron diffraction data.