• Synthesis of 3', 5'-cyclic diguanylic acid (c-di-GMP) analogues

      Heidari, Nazanin; Department of Chemistry
      In the past few years, interest in signaling networks involving 3ʹ, 5ʹ -cyclic diguanylic acid (c-di-GMP) has increased dramatically. Evidence started to emerge that connects c-di-GMP to the regulation of a range of biological processes in bacteria, such as bacterial biofilm formation, virulence, extracellular polysaccharide synthesis, however, much remains to be explored in the signaling pathways that involve this secondary messenger. This molecule has also been shown to be a very powerful immunostimulating agent and potent mucosal vaccine adjuvant.
    • Synthesis of 3’, 5’-cyclic diguanylic acid (c-di-GMP) as mucosal vaccine adjuvant and bacterial second messenger

      Milah, Khatma; Department of Chemistry
      The present study describes the synthesis of 3’,5’- cyclic diguanylic acid (c-di-GMP), attempts were made to synthesize guanosine bearing a 2’-O-(hexyn-6-yl)- and 2’-O-(6-azidohexyl)-modification using 2,6-diaminopurine riboside as starting material. The synthesis of 2’-O-(hexyn-6-yl) guanosine started with the alkylation of 2,6-diaminopurine riboside with 6-iodo-1-hexyne, which gave a mixture of 2’- and 3’-O-alkylated 2,6-diaminopurine riboside. Treatment of this product with isobutyryl chloride, followed by ammonium hydroxide gave N2-isobutyryl-2’-O-2’-O-(hexyn-6-yl)-2,6-diaminopurine riboside. Subsequent deamination reaction was carried out with sodium nitrite in a mixed solvent gave the desired N2-isobutyryl-2’-O-2’-O-(hexyn-6-yl) guanosine. N2-Isobutyryl-2’-O-(6-azidohexyl) guanosine was also obtained in the similar manner. Synthesis of a second building block, a suitably protected guanosine H-phosphonate was also attempted using guanosine as starting material. Experimental and spectral data are provided for new compounds.
    • Synthesis of 4-hydroxycinnamic amides of di-, tri-, and tetraamines : potential insect toxins /

      Fixon-Owoo, Solomon N. K.; Department of Chemistry (Brock University, 2000-05-21)
      The monoconjugates of phenolic acids (i.e. coumaric acid) with polyamines such as spermidine and spermine are strikingly similar to some toxins from spiders and predatory wasps. Many plants contain phenolic acid polyamine conjugates and there is some reliable information supporting their roles as plant defense chemicals. Eleven monoacylated compounds of diamines, triamines, tetraamines and oxa-polyamine amines were prepared in three to seven steps: 22, 23, 24, 25, 26, 27, 28, 29, 30, 31 and 32. The synthesis proceeds through stepwise construction of the polyamine backbone (as in 62 and 72), followed by protection and deprotection steps of the amino functions. Desymmetrization of readily available and prepared symmetrical polyamines is a key step in the synthesis. The protecting groups employed were tert-butoxycarbonyl (BOC) and trifluoroacetyl (TFA) group which were removed under different conditions: acid and base respectively. Deprotection and refunctionalization of the polyamine reagent demonstrated the versatility of these systems for N-acylation.
    • Synthesis of a 7-Membered Biaryl Guanidine Catalyst and its Use in the Vinylogous Aldol Reaction

      Hassan, Mohamed; Department of Chemistry (Brock University, 2014-07-23)
      The present thesis outlines the preparation of a 7-membered guanidine. Initial efforts to obtain this guanidine via 2-chloro-1,3-dimethylimidazolinium chloride induced ring forming chemistry failed to provide the target in a reproducible fashion. Changing strategies, we were able to obtain the desired guanidine through CuCl mediated amination of a 7-membered thiourea intermediate to arrive at the target. In addition, the catalytic activity of this compound was evaluated in a vinylogous aldol reaction of dibromofuranone and four aromatic aldehydes to generate chiral γ-butenolides with modest to good enantiomeric excess. It was found that electron-poor aldehydes resulted in higher, 81% ee, whereas electron rich aldehydes led to low, 41% ee, levels of enantiomeric excess.
    • The synthesis of a-Tocohexaenol, a new fluorescent analogue of a-Tocopherol

      Wang, Yongsheng.; Department of Chemistry (Brock University, 2008-11-04)
      Since its discovery in 1922, vitamin E has been widely investigated for its role as a powerful, chain-breaking antioxidant that is required for human health. However, some basic issues still remain unclear, such as the mechanism and dynamics of the intracellular trafficking of a-tocopherol. To better understand tocopherol's biological activity at the cellular level, fluorescence spectroscopy and microscopy have been found to be valuable tools. This thesis reports the synthesis of a new fluorescent analogue of a-tocopherol, atocohexaenol, an intrinsically fluorescent analogue of a-tocopherol. Different methodologies of preparation have been attempted and a strategy using a preformed chromanol head plus ClO and Cs portion of the polyene side chain finally provided us the desired a-tocohexaenol. a-Tocohexaenol shows a strong fluorescence in both ethanol and hexanes with maximum Aab = 368 nm and maximum /...em = 521 nm. This compound is stable for a couple of weeks in ethanol or hexane solution if stored at 0 °C and protected form light. It decomposes slowly at room temperature and light will accelerate its decomposition (within 5 hours). Thus, a-Tocohexaenol may be a useful fluorescent probe to study the biochemistry and cell biology of vitamin E.
    • Synthesis of Chiral Benzimidazolylidenes from 1,10-Phenathrolines and 1,10-Phenathroline-2,9-dione /

      Wang, Yao.; Department of Chemistry (Brock University, 2007-06-29)
      A^-heterocyclic carbenes (NHCs) have become the focus of much interest as ancillary ligands for transition metal catalysts in recent years. Their structural variability and strong cy-donation properties have led to the preparation of demonstrably useful organometallic catalysts. Among the three general structural types of NHCs (imidazolylidenes, imidazolinylidenes, and benzimidazolylidenes), benzimidazolylidenes are the least investigated because of the limitation of current synthetic approaches. The preparation of chiral analogues is even more challenging. Previously, our group has demonstrated an alternative approach to synthesizing benzimidazolylidenes with a tetracyclic framework in three steps from 1,10-phenanthroline. This thesis is focused on approaches to chiral benzimidazolylidenes derived from substituted 1,10-phenanthrolines. A key step in the preparation of these ligands involves a reduction of the pyridyl rings in 1,10-phenanthrolines. Chirality can be introduced to phenanthrolines before, during, or after the reduction as illustrated by three approaches: 1) de novo construction of the phenanthroline from chiral ketones with endo and exo faces to provide a degree of diastereoselectivity during subsequent reduction; 2) introduction of substituents into the 2- and 2,9- position of phenanthroline by nucleophilic aromatic substitution, followed by a reduction-resolution sequence; and 3) use of the protected octahydrophenanthroline as a substrate for chiral induction a to nitrogen.
    • SYNTHESIS OF CYCLIC AZOBENZENE ANALOGUES FOR INCORPORATION INTO OLIGONUCLEOTIDES, PEPTIDES AND POLYMERS

      Joshi, Dhruval Kumar; Department of Chemistry (Brock University, 2014-02-21)
      (A) In recent years, considerable amount of effort has contributed towards enhancing our understanding of the new photoswitch, cyclic azobenzene, particularly from the theoretical point of view. However, the challenging part with this system was poor efficiency of its synthesis from 2,2’- dinitrodibenzyl and lack of effective methods for further modification which would be useful to incorporate this system into biomolecules as a photoswitch. We report the synthesis of cyclic azobenzene and analogues from 2,2’-dinitrodibenzyl, which would allow for further incorporation of this cyclic azobenzene into biomolecules. Reaction of 2,2’-dinitrodibenzyl with zinc metal powder in the presence of triethylammonium formate buffer (pH-9.5) gave a cyclic azoxybenzene, 11,12-dihydrodibenzo[c,g][1,2]diazocine-5-oxide. The latter compound was converted into cyclic azobenzene analogues (bromo-, chloro-, cyano-, and carboxyl) through subsequent transformations. The carboxylic acid analogue was reacted with D-threoninol to give the corresponding amide, which readily undergoes photo-isomerization upon illumination with light. Upon illumination with light at 400 nm, approximately 70% of cis- isomer of amide was isomerized to trans- isomer. It was observed that cis- to trans- isomerization reached the maximum steady state of light transmission after approximately 40 min, whereas the trans- to cis- isomerization approximately acquired in 2 h to regain full recovery of light transmission. Cyclic azobenzene phosphoramidite was synthesized from DMT-protected D-threoninol linked cyclic azobenzene. (B) In recent years, there has been considerable interest invested towards the synthesis of azobenzene analogues for incorporation into proteins. Among the many azobenzene analogues, the synthesis of bi-functional cyclic azobenzene analogues for the incorporation into proteins is relatively new. In this thesis, we report the synthesis of a cyclic azobenzene biscarboxylic acid from 4-(bromomethyl)benzonitrile. (C) Azobenzene has been widely used in the field of polymer science to study the surface morphology and surface properties of polymers. In this thesis, we report the incorporation of cyclic azobenzene into a commercial polymer 2- (hydroxyethyl)methacrylate. Samples collected after 24 h from the reaction solution showed approximately 9% of incorporation of cyclic azobenzene into polymer compared to samples collected after 10 h, which showed approximately 6% incorporation.
    • Synthesis of fluorinated nucleosides for probing DNA conformations via 19F NMR spectroscopy

      Solodinin, Andrei; Department of Chemistry
      Work described in this thesis explored the synthesis of 5-fluoro-2’-deoxycytidine and 8-fluoro-2’-deoxyguanosine, and subsequent incorporation of these modified nucleosides into d(CG) repeat oligonucleotides through the phosphoramidite chemistry-based solid phase synthesis, in order to investigate the B-Z junction through 19F NMR spectroscopy. Toward this goal, 5-fluoro-2’-deoxycytidine was successfully synthesized from 5-fluoro-2’-deoxyuridine. Choices of protecting groups for the exocyclic amine of 5-fluoro-2’-deoxycytidine were examined, and N-acetyl was found to be most suitable in terms of the stability of the protected nucleoside and the readiness of its removal. 8-Fluoro-2’-deoxyguanosine was prepared by fluorination of suitably protected 2’-deoxyguanosine using N-fluorobenzenesulfonimide as the fluorinating agent. Circular dichroism and UV/vis spectroscopic studies showed that the fluoro-modification does not affect the overall conformation of the oligonucleotides, both in the B- and Z-form. 19F NMR spectra of single fluoro-modified d(CG)6 sequence at 3’-end (11-FdC) were recorded in solution containing 0.1 – 4 M NaCl. The results supported a theoretical model for B-/Z-DNA transition, where initiation starts from the ends, progressing to eventual transition.
    • Synthesis of Heteroleptic Redox-active and Spin-crossover Complexes

      Pelaccia, Mark; Department of Chemistry
      The following research regarding heteroleptic redox-active complexes with the potential for spin-crossover is synthetic in nature. The intent behind incorporating the Schiff base ligand N-(8-quinolyl)salicylaldimine with some redox-active species into a mixed ligand complex featuring a d4-d7 metal ion center was to prime the material for spin-crossover based on strong intermolecular interactions that would enhance cooperativity of the system. Single component systems that display spin-crossover behaviour paired with other physical properties like electrical conductivity hold significance in the field of multifunctional materials, of which there are few examples that feature mixed ligand systems. Information describing this type of chemistry and the magnetic interactions that govern these characteristics is introduced in the first chapter of this work. The synthetic strategies toward mixed ligand complexes in the form of [(Qsal)Fe(RAL)]+X- and [(Qsal)Co(RAL)]+X- have been realized from the use of mononuclear [(Qsal)FeCl2(CH3OH)] and [(Qsal)Co(OAc)]+OAc- species, respectively. The redox-active ligand (RAL) component is an arylazo ligand like 10-(8-quinolylazo)-9-phenanthrol (Qapl) or 1-(2-Pyridylazo)-2-phenanthrol (Papl), which possess a low-lying π* MO that makes them susceptible to multi-step reductions that give rise to radical intermediates. Heteroleptic complexes that were synthesized and isolated like [(Qsal)Fe(Qapl)]+BPh4-, [(Cl-Qsal)Fe(Qapl)]+BPh4-- and homoleptic [Fe(Qapl)2]+BPh4- were diffracted and measured several intermolecular π-π contacts of distances typically between 3.5-3.7 Å, often between the phenanthrene rings of adjacent Qapl ligands. Complexes In the form of [(Qsal)Fe(Qapl)]+X (X= BPh4- or SCN-) showed early onset of spin transition in solution usually beyond 298 K. These complexes were overly reduced in the glovebox which resulted in their deterioration, presumably from the cleavage of the RAL azo bond. The framework developed for the heteroleptic Fe3+ coordination chemistry was applied to cobalt, with some amendments, and afforded several heterleoptic Co3+ complexes using Qsal with the arylazo ligands Qapl and Papl. The heteroleptic cobalt complexes presented here were found to be LS Co3+ which is diamagnetic. However, there is potential under inert atmosphere to produce Co2+ and possibly a phenoxyl radical species with redox-active valence tautomers.
    • The Synthesis of Imidazole Fatty Acid Conjugates as Inhibitors of Apoptosis

      Venkata Krishna Rao, Garapati; Department of Chemistry (Brock University, 2013-03-14)
      Ionizing radiation is known to initiate apoptosis in mammalian cells by causing the transformation of cytochrome c into a peroxidase, which results in the specific peroxidation of the mitochondrial phospholipid cardiolipin. Here we report the design and synthesis of 8 imidazole fatty acid derivatives that bind to the cyt c:CL complex and inhibit the peroxidase activity required for the initiation of apoptosis. We postulate that imidazole acts as a sixth ligand to the haem iron and stops the interaction with H2O2. Two mitochondrially directed analogues (3-hydroxypropyl)triphenylphosphonium esters) of 12-imidazole-stearic acid and 12-imidazole-oleic acid not only were demonstrated to be peroxidase inhibitors in vitro, but were also extraordinarily effective in protecting mice from lethal doses (9 Gy) of ionization radiation. We studied the structure activity relationship to a group of triphenyl phosphonium derivatives containing imidazole at different positions on the fatty acid chain, and observed that the C8-imidazole stearate analogue had marginally better activity than the others. But overall, the structure activity result were remarkable “flat” with all compounds prepared having rather similar inhibitory strength. We also synthesized carnitine mono and di-esters of 12-imidazole fatty acids but full biological data is not yet available for these compounds.
    • Synthesis of isotope-labelled methoxypyrazine compounds as internal standards and quantitative determination of aroma methoxypyrazines in water and wines by solid-phase extraction with isotope dilution-GC-MS /

      Chen, Xiaonan.; Department of Chemistry (Brock University, 2005-06-15)
      An efficient way of synthesizing the deuterium labelled analogues of three methoxypyrazine compounds: 2-d3-methoxy-3-isopropylpyrazine, 2-d3-methoxy-3- isobutylpyrazine, and 2-d3-methoxy-3-secbutylpyrazine, has been developed. To confirm that the deuterium labels had been incorporated into the expected positions in the molecules synthesized, the relevant characterization by NMR, HRMS and GC/MS analysis was conducted. Another part of this work involved quantitative determination of methoxypyrazines in water and wines. Solid-phase extraction (SPE) proved to be a suitable means for the sample separation and concentration prior to GC/MS analysis.Such factors as the presence of ethanol, salt, and acid have been investigated which can influence the recovery by SPE for the pyrazines from the water matrix. Significantly, in this work comparatively simple fractional distillation was attempted to replace the conventional steam distillation for pre-concentrating a sample with a relatively large volume prior to SPE. Finally, a real wine sample spiked with the relevant isotope-labelled methoxypyrazines was quantitatively analyzed, revealing that the wine with 10 beetles per litre contained 138 ppt of 2-methoxy-3-isopropylpyrazine. Interestingly, we have also found that 2-methoxy-3-secbutylpyrazine exhibits an extremely low detection limit in GC/MS analysis compared with the detection limit of the other two methoxypyrazines: 2- methoxy-3-isopropylpyrazine and 2-methoxy-3-isobutylpyrazine.
    • Synthesis of nanoporous materials for preconcentration and determination of trace elements by ICP-AES ; Investigation and elimination of the memory effects of mercury, gold, silver and boron in ICP-AES

      Chen, Wencan.; Department of Chemistry (Brock University, 1999-07-09)
      Nanoporous materials with large surface area and well-ordered pore structure have been synthesized. Thiol groups were grafted on the materials' surface to make heavy metal ion pre-concentration media. The adsorption properties ofthe materials were explored. Mercury, gold and silver can be strongly adsorbed by these materials, even in the presence of alkaline earth metal ion. Though the materials can adsorb other heavy metal ions such as lead and copper, they show differential adsorption ability when several ions are present in solution. The adsorption sequence is: mercury> == silver> copper » lead and cadmium. In the second part of this work, the memory effects of mercury, gold, silver and boron were investigated. The addition of 2% L-cysteine and 1% thiourea eliminates the problems of the three metal ions completely. The wash-out time for mercury dropped from more than 20 minutes to 18 seconds, and the wash-out time for gold decreased from more than 30 minutes to 49 seconds. The memory effect of boron can be reduced by the use of mannitol.
    • The Synthesis of Phosphatidylinositol Bolalipids

      Jewell, Shannon; Department of Chemistry
      This thesis describes the attempted synthesis of phosphatidylinositol bolalipids to be used in the investigation of the mechanism of the phosphatidyl inositol transfer protein, Sec14, and the PI(4)-kinase, Pik1. The synthesis of two unique bolalipids was the goal of this thesis. The esterification of the sn1 position of a protected glycerol unit to stearic acid as well as esterification at the sn2 position to either the C20 or C36 diacid gave the framework of the desired bolalipid. Further success was seen in the coupling of benzyloxybis(diisopropylamino) phosphine to the sn3 position of the deprotected glycerol unit in the generation of a phosphoramidite. However, efforts in the final step of the synthetic method were unsuccessful and did not lead to the complete synthesis of the bola-PI. Though it was possible to couple the 2,3,4,5,6-benzyl protected myo- inositol to the phosphoramidite, the most significant issues in the synthesis of the bola-PI is the oxidation of the phosphite to the phosphonate. Despite multiple attempts with varying oxidizing agents, no oxidation was observed by TLC, P NMR or mass spectrometry data. Two phosphoramidites, precursors to the desired bola-PI molecules, have been synthesized to date. The two phosphoramidites were characterized by H NMR, C NMR, P NMR, mass spectrometry, and optical activity. They are both air and water sensitive and have been observed to decompose with storage, even when placed under nitrogen at -4 oC. Spectral and experimental data are provided for all new compounds.
    • Synthesis of photoaffinity analogues of alpha-tocopherol /

      Lei, Huangshu (John); Department of Chemistry (Brock University, 1999-05-21)
    • The Synthesis of α-Tocopentaenol (αT5), a Fluorescent Analogue of α-Tocopherol

      Hildering, Andrew; Department of Chemistry
      This thesis is focused on the investigation of synthesizing a fluorescent analogue of vitamin E, α-tocopentaenol (αT5). α-Tocopentaenol contains five conjugated double bonds across the phytyl tail, resulting in its fluorescence characteristics. Different methodologies of preparation were attempted to synthesize an all trans-configuration in the five-conjugated double bonds. Unfortunately, across the C3’ bond on the tail, geometric isomers were obtained. However, TBSO-αT5 was produced in what appeared to be ≈ 2:1 E:Z mixture across the C3’ bond (having the four other olefins with trans-configurations). α-Tocopentaenol showed a strong absorbance in ethanol with a maximum λab= 338 nm. This compound is stable as an oil, stored at -78˚C and protected from light for over a month with minimal degradation. Because αT5 resembles the naturally occurring form of the vitamin E, this analogue will enhance our ability to study the biological activity of vitamin E and will create an easy method of monitoring its presence in solution and cells.
    • Synthesis, Catalysis and Stoichiometric Reactivity of Mo Imido Complexes

      McLeod, Nicolas A.; Department of Chemistry (Brock University, 2014-05-07)
      The syntheses, catalytic reactivity and mechanistic investigations of novel Mo(IV) and Mo(VI) imido systems is presented. Attempts at preparing mixed bis(imido) Mo(IV) complexes of the type (RN)(R′N)Mo(PMe3)n (n = 2 or 3) derived from the mono(imido) complexes (RN)Mo(PMe3)3(X)2 (R = tBu (1) or Ar (2); X = Cl2 or HCl, Ar=2,6-iPr2C6H3) are also described. The addition of lithiated silylamides to 1 or 2 results in the unexpected formation of the C-H activated cyclometallated complexes (RN)Mo(PMe3)2(η2-CH2PMe2)(X) (R = Ar, X = H (3); R = tBu, X = Cl (4)). Complexes 3 and 4 were used in the activation of R′E-H bonds (E = Si, B, C, O, P; R′ = alkyl or aryl), which typically give products of addition across the M-C bond of the type (RN)Mo(PMe3)3(ER′)(X) (4). In the case of 2,6-dimethylphenol, subsequent heating of 4 (R = Ar, R′ = 2,6-Me2C6H3, E = O) to 50 °C results in C-H activation to give the cyclometallated complex (ArN)Mo(PMe3)3(κ2-O,C-OPh(Me)CH2) (5). An alternative approach was developed in synthesizing the mixed imido complex (ArN)(tBuN)Mo(PMe3)(η2-C2H4) (6) through EtMgBr reduction of (ArN)(tBuN)MoCl2(DME) in the presence of PMe3. Complex 6 reacts with various hydro- and chlorosilanes to give β-agostic silylamido complexes and in one case, when Me2SiHCl is the silane, leads to the silanimine complex (tBuN)Mo(η2-SiMe2-NAr)(Et)(η2-C2H4) (7). Mechanistic studies on the formation of the Mo(VI) tris(silyl) complex (tBuN)Mo(SiHPh)(H){(μ-NtBu)(SiHPh)}(PMe3)2 (8) were done from the addition of three equivalents of PhSiH3 to (tBuN)Mo(PMe3)(η2-C2H4), resulting in identification of β- and γ-agostic SiH…Mo intermediates. The reactivity of complex 8 towards ethylene and nitriles was studied. In both cases coupling of unsaturated substrates with the Mo-Si bond of the metalacycle was observed. In the case of nitriles, insertion into the 4-membered disilaazamolybdacycle results in complexes of the type (tBuN)Mo{(κ2-Si,C-SiHPh-NtBu-SiHPh-N=C(R)}(PMe3)2. Catalytic hydrosilylation of carbonyls mediated by the β-agostic silylamido complex (ArN)2Mo(η3-NtBu-SiMe2-H)(H) (9) was investigated. Stoichiometric reactions with organic substrates showed that catalysis with 9 does not proceed via the conventional insertion of substrate into the Mo-H bond.
    • Synthesizing Self-Healing and Recyclable Silicones Using the Diels-Alder Reaction as a Cross-Linker: Investigation of Various Dienes and Dienophile Systems

      Azadi Namin, Paria; Department of Chemistry
      This thesis focuses on the synthesis of recyclable and self-healing polysiloxane elastomer networks. These features were achieved through the use of thermally reversible Diels-Alder (DA) and retro-Diels-Alder (rDA) reactions. In this work, for the model system, two different dienes (3 and 8) and six dienophile were explored, of which five of the dienophiles are commercially available and one of them was synthesized in the lab (13) to produce a series of model DA adduct. Model systems consisting of diene-functionalized trisiloxanes and bismaleimides as dienophiles were utilized to develop a fundamental understanding of how the electronic differences in the coupling systems would influence the efficiency of the overall reaction. Then for the elastomers, three different methylhydrosiloxane-dimethylsiloxane copolymer, trimethylsiloxane terminated (PDMS) with different molecular weights and Si-H group mole percentages [32 a = 3-4% Si-H and 13000 g/mol; 32 b = 7-9% Si-H and 5500-6500 g/mol; 32 c = 25-30% Si-H and 2000-2600 g/mol] were used and functionalized with two different dienes (3 and 8) to produce six polymeric diene systems (33 a, 33 b, 33 c, 34 a, 34 b and 34 c). After analyzing the model systems, the optimal temperature for adduct formation was determined to be between 60 °C – 70 °C, while the rDA reactions occur were found to occur between 90 °C and 110 °C , depending on the system. The tensile strengths of the elastomer systems correlated well with the cross-link densities of individual elastomers (elastomers were elongated between 0.3 cm and 2.54 cm). Furthermore, the hardness of the elastomers also correlated with the cross-link density of the elastomer (Shore 00 values ranged from 32 to 8 ). However, all of the elastomers displayed a decrease in their Shore 00 values after being damaged and healed. Of particular note in this study are elastomers 35 b and 35 c. Not only were these the only examples of translucent and colourless materials, the elastomers fully cured at room temperature in only 5 h. After mechanical damage the elastomers were heated to 80 °C to induce mobility in the polymer chains, complete healing of the mechanical damage was observed to occur in approximately 3 min and upon cooling to room temperature it cured and got solid again.
    • Synthetic Approaches to C-1 Derivatives of Pancratistatin

      Uppalapati, Bhavana; Department of Chemistry
      The contents of this thesis describe a synthetic approach towards C-1 derivatives of pancratistatin, utilizing a previously published pathway to access a late-stage cis-diol. The key steps of the approach include enzymatic dihydroxylation to provide the C-ring backbone, Myers’ transposition to convert an allylic alcohol into an olefin, and nucleophilic substitution of a tosylate to insert carbon-based nucleophiles at C-1. Experimental and spectral data are provided for the novel compounds.
    • Synthetic approaches to syn-diol containing biologically active compounds /

      Mao, Justin Y.; Department of Chemistry (Brock University, 2002-05-19)
      The deoxy derivative of pancratistatin 1.10 was prepared in good yield through the use of a [4+2] Diels-Alder cycloaddition and Bischler-Napieralski cyclization approach. The Bischler-Napieralski cyclization was shown to yield two additional side products 2.9, 2.10, however, under slightly modified hydrolysis conditions, the tetracyclic product 2.11 was obtained exclusively in greater than 84% yield. Initial screening of the di-hydroxylatgd derivative, and the other complementary pair analogue 1.10' previously prepared in our laboratories gave interesting results. Both of these compounds were shown to exhibit cytostatic activity; the mono-alcohol was marginally active while the di-hydroxylated analogue proved to be more potent although one to two magnitudes less potent than pancratistatin itself Human tumour cell line assay results indicated that the di-hydroxylated derivative exhibited selective cytotoxic inhibition in the following cell lines: non-small cell lung cancer line NCI-H226 (ED50 - 0.65 ^g/mL), leukemia cell lines CCRF-CEM (ED30 = 0.55 Hg/mL) and HL-60(TB) (ED50 = 0.89^ig/mL). Our results demonstrated that the pharmacophore is not a mono-alcohol, and that the minimum pharmacophore contains the hydroxyl group at the C4 position in addition to either, or both, of the hydroxyl groups present at C2 and C3.' The minimum pharmacophore has been narrowed to only three possibilities which are current synthetic targets in several research groups. The controlled Grignard addition to the tartaric acid derived bis-Weinreb amide 1.25 afforded a direct entry to a host of 1,4-diflferentiated tartaric acid derived intermediates (2.12-2.18). This potentially usefiil methodology was demonstrated through the efficient synthesis of the naturally occurring lactone 2.23, which bears the inherent syn-dio\ subunit. Based on this result, a similar approach to the synthesis of syn-dio\ bearing natural products looks very promising? A direct 2,3-diol desymmetrization method using TIPS-triflate was shown to be effective on the selective differentiation of Z,-methyl tartrate (and diisopropyl tartrate). The mono-silyl-protected intermediates 2.31 also proved to be useful when they were selectively differentiated at the 1,4-carboxyl position (2.35, 2.36) through the use of a borohydride reducing agent. Furthermore, the mono-silyl-protected derivative underwent periodate cleavage affording two synthetically useful a,P-unsaturated esters 2.43, 2.44, with one of esters being obtained via a silyl-migration method.''
    • Synthetic studies on prostaglandins: "synthesis of a new thia-PGEI analog"

      Ratemi, Elaref S.; Department of Chemistry (Brock University, 1992-07-09)
      A PGE1 analog, namely (±)-trans-2-(6'-carbomethoxyhexyl)-3- (E-3"-thia-1 "-octene)-4-hydroxycyclopentanone 71, has been prepared for the first time. Towards the synthesis of this compound, several synthetic approaches aimed at the preparation of the required acetylenic and E-halovinylic sulfides as building blocks were investigated. Among all the methods examined, it appeared evident that the best route to ethynyl n.pentyl sulfide 81 is via a double dehydrohalogenation of the corresponding 1,2-dibromoethyl sulfide with sodium amide in liquid ammonia. In addition, the isomerically pure E-2-iodoethenyl n.pentyl sulfide 85 is conveniently prepared in high yield and stereoselectivity by hydrozirconation-iodination of the terminal ethynyl sulfide 81. The classical hydroalumination and hydroboration reactions for the preparation of vinyl halides from alkynes gave only small yields when applied as methods towards the synthesis of 85 . The building block 2-(6'-carbomethoxyhexyl)-4-hydroxy-2- cyclopentenone (±)-1 carrying the upper side-chain of prostaglandin E 1 was prepared by a step-wise synthesis involving transformations of compounds possessing the required carbocyclic framework (see scheme 27). The synthesis proved to be convenient and gave a good overall yield of (±)-1 which was protected as the TH P-derivative 37 or the siloxy derivative 38. With the required building blocks 81 and 37 in hand, the target 1S-thia-PGE1 analog (±)-71 was prepared via the in situ higher cuprate formation-conjugate addition reaction. This method proved to be convenient and stereospecific. The standard cuprate method, involving an organocuprate reagent generated from an isolated vinyl iodide, did not work well in our case and gave a complicated mixture of products. The target compound will be submitted for assessment of bio log ical activity.