Browsing by Subject "Alkenes"
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Item Characterization of the brood cuticular hydrocarbons of the fire ant Solenopsis Invicta and their possible role in brood recognition by workers(Texas Tech University, 2004-12) Al Diri, IssamChromatography and mass spectrometry analysis were used to identify and quantify 14 cuticular hydrocarbons in the developmental stages of S. invicta. The following quantitative and qualitative differences in hydrocarbons were observed among brood components. Cuticular hydrocarbons consisted of saturated n-alkanes and methylalkanes, ranging from C23 to C29. The total amount of cuticular hydrocarbons was greatest in prepupae and least in pupal stages. While the total amount of cuticular hydrocarbons was several magnitudes greater in components of sexual brood, as expected since sexual forms are larger than worker forms, the ratio of n-alkanes to methylalkanes in worker brood was generally higher than its counterparts in sexual brood. Discriminant function analysis of the brood subcastes using the five most abundant hydrocarbons within and among colonies showed that the brood subcastes clustered together based on their respective developmental stage, with n-heptacosane being the major component responsible for the observed clustering. Finally, several bioassays were conducted to determine whether cuticular hydrocarbons play a role in brood recognition. Worker retrieval response toward pupae immersed in hexane for 5 min was significantly lower than that towards a control. Immersing pupae in boiling water for 3 sec. also induced a similar response to that caused by hexane. Several concentrations of cuticular extracts in hexane of sexual prepupae applied to a paraffin dummy failed to induce any retrieval response by workers. In addition, manipulation of the composition of brood cuticular hydrocarbons did not seem to affect worker response toward the brood. Taken together, the results suggest that a chemical signal other than cuticular lipids is involved in brood recognition.Item Electrochemical investigations of the reactions of nickel phenanthroline derivatives with alkyl bromides and activated olefins(Texas Tech University, 1982-05) Kuo, Yang-mingNot availableItem Electrochemical study of the catalytic properties of cobalt 2,2'-bipyridine complexes with n-alkyl bromides and selected olefins(Texas Tech University, 1982-05) Caron, Linda MarieNOT AVAILABLEItem I. The synthesis of homoallylic amines via a 1,2-metalate rearrangement; II. The synthesis of bridged azabicyclic structures via ring-closing olefin metathesis(2003-05) Neipp, Christopher Ernest; Martin, Stephen F.A convergent, stereoselective route to homoallylic sulfonamides has been described. Homoallylic sulfonamides with di- and trisubstituted double bonds were prepared in good yields and with excellent control of alkene geometry via a cuprateinduced 1,2-metalate rearrangement of α-lithiated N-trisyl 2-pyrroline. Removal of the N-trisyl group was achieved by sonication of the sulfonamides in the presence of Li(0) wire and catalytic di-tert-butylbiphenyl. The utility of this method was illustrated by its application toward the synthesis of a squalene synthetase inhibitor. In other efforts, a versatile approach to bridged azabicyclic structures was developed. This process involved the ring-closing metathesis (RCM) of cis-2,6- dialkenyl N-acyl piperidines, which were prepared in six steps from glutarimide or in three steps from 4-methoxypyridine. The N-acyl protecting group of these piperidines played a crucial role in this sequence by stabilization of the C2,C6 bisaxial conformers necessary for their RCM. In this manner, a diverse array of bridged azabicyclic structures were obtained in excellent yields. Application of this RCM strategy toward the synthesis of (±)-cocaine and compounds structurally related to vellosimine has been reported.Item New metal-assisted synthesis of functionalized olefins(Texas Tech University, 2003-08) Karur, SubramanianThis thesis describes new methodologies for the synthesis of â-substituted Baylis- Hillman and related adducts using stoichiometric amounts of Lewis acids, titanium tetrachloride and diethylaluminum iodide. The first palladium-catalyzed addition of N,N-dichlorosulfonamides to internal alkynes is also described. The TiCl4-mediated conjugate addition of halide anions to ethyl vinyl ketone and subsequent trapping of the titanium enolate with aldehydes resulted in p-halo aldol products with syn/anti selectivity up to 8.4/1.0. These halo aldol products can be converted to the corresponding Baylis-Hillman adducts by the treatment with tertiary amines. The EtiAlI-promoted Baylis-Hillman reaction of a.p-unsaturated 5-lactones is achieved for the first time. The Baylis-Hillman adducts are obtained in 50-73% chemical yields. Electron-donating aldehydes required higher temperature and gave lower yields compared to electron-withdrawing aldehydes. The first palladium acetate catalyzed aminohalogenation of internal alkynes with N,N-dichlorosulfonamides gave haloamine functionalized alkenes. The resulting enamides can serve as important versatile building blocks for organic synthesis.Item Orientation in vinyl activated 1,2-elimination reactions(Texas Tech University, 1979-05) Haines, Jeffrey CharlesNot availableItem Preparation of Substituted Enol Derivatives from Terminal Alkynes and Progress Toward the Total Synthesis of Nigricanoside A(2011-02-01T19:34:34Z) DeBergh, John Robbins; Ready, JosephThis manuscript consists of two chapters. The first chapter describes the preparation of stereodefined enol derivates of alpha-branched aldehydes from terminal alkynes. Specifically, alkenyl alanes, derived from the methylalumination of alkynes, are shown to be efficiently oxygenated with peroxyzinc species. The resulting metallo-enolate may be trapped with benzoic anhydride, acetic anhydride, and TESOTf to generate E-trisubstituted enol esters and silanes. Traditional approaches to these types of olefins involve enolization of aldehydes; these methods are often inefficient and generally afford mixtures of olefin stereoisomers. Therefore, the methodology presented Chapter One represents a conceptually novel and useful strategy. The development and scope of the methylalumination-oxygenation reaction is discussed along with applications of the enol derivatives in the context of asymmetric and natural product synthesis. Finally, the alkenyl alane intermediates are shown to be efficiently aminated to afford ene-hydrazine products. The second chapter involves the progress towards the asymmetric synthesis and structural assignment of nigricanoside A, a potent antimitotic glycolipid isolated from marine green algae. A convergent synthetic route is presented along with an analysis the natural product’s relative and absolute stereochemistry. Various diastereomers of orthogonally protected subunits of nigricanoside A were prepared through vinyl-metal additions to alpha-hydroxy aldehydes. The chapter includes attempts to join the subunits through etherification reactions as well as descriptions of future strategies to effect etherification.Item Protein engineering on soybean sterol methyl transferase leads to altered substrate binding and catalysis(Texas Tech University, 2004-12) Sinha, ArchanaSterol methyltransferases (SMTs) are ubiquitously represented in plants and they can serve as the rate-limiting enzymes in the 24-alkyl sterol (phytosterol) pathway. Together these enzymes are capable of converting sterol acceptors with a 24(25)-double bond (cycloartenol, CA; CI-activity) or 24(28)-double bond ((24)28-methyleneIophenol, ML; -C2-activity) in the sterol side chain into more that 60 distinct phytosterols in a single plant. Recently, we discovered using the soybean SMT that depending on the nature of the substrate olefin bound to SMT, either one or two catalytic reactions can proceed, concerted or step-wise, to generate the product diversity. To investigate the proposed role of aromatic amino acids that are part of a signature motif in the active site of SMT enzymes- F82YEYGWG88, Y83L and Y83F mutants were prepared and purified to homogeneity and the steady-state kinetic parameters were determined as described in this laboratory for the wild-type soybean SMT. The Y83L mutant performed much like the wild-type enzyme in terms of substrate acceptability, product distribution and physical property, but differences were detected in Y83F mutant. "When the mutant SMT activities were compared to the native SMT activities in relation to inhibition by 25- azacycloartenol (transition state analog) or 26,27-dehydrocycloartenol (mechanism based inhibitor), both sets of enzymes were found to be inhibited with equal efficacy, suggesting that the successive C-methylation of the Ä24 bond occurs at the same active center. Based on activity assays performed over the temperature range 15 to 40''C, the activation energy (Eact in KJ/mol) estimated from the Arrhenius plots were found to be: (i) wild-type, CA = 49, ML = 71; (ii) Y83F, CA = 65, ML = 52 and (iii) Y83L, CA = 98, ML =185. Analysis of the pH dependence of log kcat/Km for the wild-type and two mutants showed different profiles for Ä 24(25) and Ä24(28) -substrates. The results of the mutational and kinetic analyses are interpreted to imply that product diversity catalyzed by the soybean SMT is made possible by the relaxed control over substrate and intermediate conformations resulting from altered cation-ð interactions in the active sites of the mutant enzyme and relates to the different mechanisms catalyzed using different olefin substrates.Item The Synthetic Utility of Enol Derivatives and the Directed Aryltitanation of Homoallylic and Allylic Alcohols(2012-07-20) Lee, Kathleen Marie Spivey; Ready, Joseph MartinThis dissertation is organized in three parts. First, enol derivatives represent important building blocks for organic synthesis. Often their olefin geometry directly translates into product diastero- and enantioselectivity. Thus, stereodefined enol benzoates are subjected to the Sharpless Asymmetric Dihydroxylation to form enantiomerically enriched alpha-hydroxy aldehydes. Due to their instability, these alpha-hydroxy aldehydes are further transformed in situ to demonstrate their utility in organic synthesis. The second and third parts address the carbometalation of two types of alkenes. While the carbometalation of alkynes is a widely used transformation, the corresponding transformation for alkenes is less developed. Directing groups, such as homoallylic and allylic alcohols, may help overcome the poor reactivity of alkenes towards carbometalation. Herein the alcohols direct a highly diastereoselective aryltitanation to the proximal carbon–carbon double bond. Reactions with homoallylic alcohols result in stereospecific aryl incorporation at the terminal carbon of the double bond while the reactions with the allylic alcohol incorporate the aryl group proximal to the alcohol and generate two new sp3 centers.