VTechWorks Repository :: Browsing by Author "Kingston, David G. I."

Browsing by Author "Kingston, David G. I."

Now showing 1 - 20 of 170

2-aroyl-4-acyl paclitaxel (Taxol) analogs
(United States Patent and Trademark Office, 2002-11-05)
2-debenzoyl-4-deacetyl paclitaxel, antineoplastic analogs thereof and intermediates are taught, as well as the formation of the compound, analogs and intermediates. The compound, analogs and intermediates may be used to form pharmaceutical compositions having anti-neoplastic activity. Further, the compound, analogs and intermediates may be used to treat cancer when applied in an effective amount by means such as a pharmaceutical composition.
2-debenzoyl-2-acyl taxol derivatives and method for making same
(United States Patent and Trademark Office, 1999-12-14)
The present invention relates to 2-debenzoyl-2-acyl taxol derivatives, analogues thereof and methods for making same. Compounds of the present invention include compounds having the general formula: ##STR1## wherein R.sub.1 is an alkyl or substituted alkyl; R.sub.2 is selected from the group consisting of H and C(O)R.sub.a ; R.sub.3 is selected from the group consisting of H, protecting groups, R.sub.b, and C(O)R.sub.b ; R.sub.4 is selected from the group consisting of H and C(O)R.sub.c, and wherein R.sub.a, R.sub.b, and R.sub.c are independently selected from the group consisting of alkyls, substituted alkyls, alkenyls, alkynyls, aryls, and substituted aryls; provided that R.sub.a is other than phenyl and 3-hydroxyphenyl.
2-Debenzoyl-2-acyl taxol derivatives and methods for making same
(United States Patent and Trademark Office, 1997-12-30)
Compounds having the general formula: ##STR1## wherein R.sub.1 is an alkyl or substituted alkyl; R.sub.2 is selected from the group consisting of H and C(O)R.sub.a ; R.sub.3 is selected from the group consisting of H, protecting groups, R.sub.b, and C(O)R.sub.b ; R.sub.4 is selected from the group consisting of H and C(O)R.sub.c, and wherein R.sub.a, R.sub.b, and R.sub.c are independently selected from the group consisting of alkyls, substituted alkyls, alkenyls, alkynyls, aryls, and substituted aryls; provided that R.sub.a is other than phenyl and 3-hydroxyphenyl.
7-deoxy-6-substituted paclitaxels
(United States Patent and Trademark Office, 1998-06-30)
The present invention concerns novel paclitaxel derivatives, their use as antitumor agents, and pharmaceutical formulations.
Abscisic acid ameliorates glucose tolerance and obesity-induced inflammation
Guri, Amir Joseph (Virginia Tech, 2007-10-19)
Obesity is a disease characterized by chronic inflammation and the progressive loss in systemic insulin sensitivity. One of the more effective medications in the treatment of insulin resistance have been the thiazolidinediones (TZDs), which act through the nuclear receptor peroxisome proliferator-activated receptor gamma (PPARgamma ). Due to the many side-effects of TZDs, our laboratory sought out a natural phytochemical, abscisic acid (ABA), with chemical similarities to TZDs. Our first study demonstrated that ABA activates PPARgamma in vitro and significantly ameliorates white adipose tissue (WAT) inflammation and glucose tolerance in db/db mice. We next further examined the effect of ABA on the phenotype of adipose tissue macrophages (ATMs). In doing so, we discovered two separate ATM populations which differed in their expression of the macrophage surface glycoprotein and maturation marker F4/80 (F4/80hi vs F4/80lo). Dietary ABA-supplementation significantly reduced F4/80hiCCR2+ ATMs and had no effect on the F4/80lo population. Utilizing a tissue-specific knockout generated through Cre-lox recombination, we were able to determine that this effect was dependent on PPARgamma in immune cells. To further characterize the differences between the ATM subsets that were affected by ABA, we performed a multi-organ assessment (i.e., WAT, skeletal muscle and liver) of the effect of diet-induced obesity on the phenotype of infiltrating macrophages and T cells into metabolic organs. Based on our new data, we formulated a model by which F4/80hiCCR2hi ATMs infiltrate WAT and ultimately induce a CD11c+ pro-inflammatory phenotype in the resident F4/80loCCR2lo subset. Ultimately, our findings provide evidence that ABA has potential as an alternative preventive intervention, expound the role of PPARgamma in immune cells and, in general, expand our knowledge concerning the immunopathogenesis of obesity-induced insulin resistance.
Activation of diboron reagents: The development of mild conditions for the synthesis of unique organoboron compounds
Thorpe, Steven Brandon (Virginia Tech, 2012-03-23)
The first successful synthesis and isolation of a boronic acid was reported in 1860 by Frankland in the pursuit of novel organometallic compounds. For more than a century, further studies of boronic acids were sparsely published. Suzuki and Miyaura jumpstarted the field in 1979 with an innovative carbon-carbon bond forming reaction employing an organoboronic acid and a carbon halide under palladium catalysis. Indeed, the Nobel Prize in Chemistry was awarded to Professor Akira Suzuki, along with Professors Richard Heck and Ei-ichi Negishi, in 2010 for their important contributions in palladium-catalyzed cross-coupling chemistry. Over the last 30 years, reports on organoboron compounds have increased exponentially. This dissertation describes the author's contributions to the development of preparative methods for organoboronic acid derivatives using transition metal-catalyzed reactions of diboron reagents. A unique "mixed" diboron reagent was developed (PDIPA diboron) that contains sp2- and sp3-hybridized boron atoms, unambiguously confirmed by X-ray crystallography. PDIPA diboron is sufficiently activated internally through a dative-bonding amine to selectively transfer the sp2-hybridized boron regioselectively, in the presence of copper, to electron deficient alkenes including α,β-unsaturated ketones, esters, amides, aldehydes, and nitriles to provide the corresponding boratohomoenolates. A unique β,β-diboration of an α,β-acetylenic ketone was also discovered. The scope of PDIPA diboron reactions was then expanded to a set of substrates with a more complex structural backbone. Allenoates are α,β,γ-unsaturated esters with orthogonal pi systems, which pose several possible difficulties with the regioselectivity of addition, not to mention known isomerizations catalyzed by copper. However, we successfully installed the boron moiety regioselectively on the β-carbon of a variety of allenoates, providing a vinyl boronic ester, and also observed exclusive formation of the (Z)-isomer from racemic starting materials. The resulting vinyl boronic ester was then shown to be an excellent Suzuki-Miyaura cross-coupling partner, affording a diastereopure, trisubstituted alkene in quantitative yield. Commercially available bis(pinacolato)diboron has shown remarkable stability towards hydrolysis and autoxidation. Using this reagent, we developed a copper- and amine-catalyzed boration protocol performed entirely in water and open to air. Using only 1 mol% copper, extraordinary activity was observed. UV-Vis, 11B NMR, and solvent kinetic isotope experiments were employed to gain insight into the mechanism, which showed the possibility of autocatalysis. Attempts to control stereoselectivity were not successful, although these results were rationalized by a dynamic catalyst structure.
Analysis of Alcohol and Alkylphenol Polyethers via Packed Column Supercritical Fluid Chromatography
Hoffman, Brian Jeffrey (Virginia Tech, 2004-05-03)
Alkylphenol ethoxylates (APEOs), alcohol ethoxylates (AEOs), and alcohol propoxylates (APOs) are non-ionic surfactants used in daily care products and detergents. They are formed as an oligomeric series with a varying distribution, which determines their commercial application. The goal of the research performed was the development of sample characterization methods for non-ionic surfactants utilizing supercritical fluid chromatography (SFC) under mild instrument operating conditions. The aryl group present in APEOs allowed ultraviolet (UV) detection, with an equal molar response for oligomers, allowing average molar oligomer values to be calculated. APEOs were separated by ethoxylate unit via SFC-UV as well as normal phase HPLC-UV employing packed columns. Stationary phase and column length were varied in the SFC setup to produce the most favorable separation conditions. Fractions from SFC runs of APEOs were collected and analyzed by flow injection analysis electrospray ionization mass spectrometry (FIA-ESI-MS) to identify fraction composition. SFC provided shorter retention times with similar resolution as HPLC for separation of APEOs and consumed a smaller amount of organic solvent. AEOs and APOs lack functionality capable of absorbing UV light outside the UV cut-off of normal organic solvents. SFC was able to separate AEOs and APOs derivatized as trimethylsilyl ethers (TMS) with pure CO2 with detection at 195 nm. The instrumental conditions, however, needed for separation necessitated high temperature and high CO2 pressure. Derivatization of alcohol polyether samples with an UV absorbing agent was achieved with phenylated disilazane-chlorosilane mixtures forming phenylsilylethers detected at 215 nm. Use of an organic solvent-modified CO2 mobile phase afforded lower pressure and temperature conditions for oligomer separation. The use of polar embedded alkyl phases combined with use of organic modified CO2 produced good resolution between oligomers. Better peak shape and shorter retention times were realized with methanol-modified CO2 than acetonitrile-modified CO2. Peak assignments were made via SFC coupled with ESI-MS detection in the positive ion mode. SFC-UV and SFC-ESI-MS data were jointly used for calculation of average molar oligomer values. Proton nuclear magnetic resonance (1H-NMR) analysis of non-derivatized samples was performed to determine average molar oligomer values and was used for comparison with values calculated from SFC-UV data.
Analysis of polar compounds by supercritical fluid chromatography
Shah, Swati H. (Virginia Polytechnic Institute and State University, 1989)
The analysis of polar compounds has been studied by SFC using 100% CO₂ or methanol modified CO₂ as the mobile phase. Both microbore packed and capillary columns are employed to separate the mixtures of steroids and agricultural compounds of various chemical classes such as amides, sulfonamides and ureas. The highly deactivated and crosslinked stationary phases used for both packed and capillary columns afford the elution of polar analytes with 100% CO₂ which in turn makes the on-line FT-IR detection of these analytes feasible. The flow cell interface is employed which provides very low detection limits. Spectra with high signal to noise ratio are obtained for the analytes with real time data acquisition. Some polar and structurally similar triazine herbicides are separated using a gradient mobile phase and a rapid separation of all the components with complete resolution is achieved. The effect of flow rate, column outlet pressure and the temperature on resolution is also studied for these analytes. The performance of microbore packed and capillary columns is compared using polar and nonvolatile solutes and the retention and resolution offered by both the columns are also compared. Several van Deemter plots are generated at various constant operating densities and temperatures. Also, the effect of density and temperature on efficiency and resolution is studied for capillary column with split and splitless injection techniques. Several conclusions regarding the favorable operating conditions in each case can be drawn based on the results obtained here.
Anionic synthesis and characterization of alkyl methacrylate containing polymeric systems
Long, Timothy E. (Virginia Polytechnic Institute and State University, 1987)
The anionic synthesis of alkyl methacrylates has received sparse attention in comparison to the synthesis of nonpolar hydrocarbon monomers such as styrene or the dienes. The two major reasons for the sluggish synthetic development of this class of polar monomers are the protic impurities present in most commercially available grades of monomer and the inherent side reactions associated with the ester functionality during anionic polymerization. However, by very carefully controlling various synthetic parameters and utilizing rigorously purified monomers, one can take advantage of the "living" nature of this polymerization to synthesize a variety of well-defined polymeric materials. Small variations in polymerization conditions drastically affect the properties of the polymers obtained. However, the effects depend largely upon the size of the ester alkyl group involved. The subtle relationships among such variables as ester alkyl group size, polymerization temperature, polymerization solvent and initiator have been explored and are discussed. Extensive thermal, microstructural and mechanical characterization reveal very interesting effects on the resulting polymer properties. Styrene-acrylic, acrylic-acrylic and diene-acrylic block copolymers have been synthesized demonstrating predictable molecular weights, narrow molecular weight distributions and controlled composition. These novel block copolymers preparation selective also serve as of acid- and hydrolysis excellent precursors for the ion- containing polymers. By of certain labile poly(alkyl methacrylate) esters and subsequent neutralization, metal carboxylates were introduced into a variety of block copolymers. In addition to the preparation of surfactant-like macromolecules and blend compatibilizers, novel ion-containing block copolymers were synthesized.
Antimalarial 5,6-Dihydro-alpha-pyrones from Cryptocarya rigidifolia: Related Bicyclic Tetrahydro-alpha-Pyrones Are Artifacts
Liu, Yixi; Rakotondraibe, L. Harinantenaina; Brodie, Peggy J.; Wiley, Jessica D.; Cassera, Maria B.; Miller, James S.; Ratovoson, F.; Rakotobe, Etienne; Rasamison, Vincent E.; Kingston, David G. I. (American Chemical Society, 2015-06-01)
Antimalarial Agents: New Mechanisms of Actions for Old and New Drugs
Ghavami, Maryam (Virginia Tech, 2018-06-29)
Worldwide, malaria is one of the deadliest diseases. In 2016 it sickened 216 million people and caused 445,000 deaths. In order to control the spread of this deadly diseases to human, we can either target the mosquito vector (Anopheles gambiae) or the parasite (Plasmodium falciparum). Due to recent emergence of resistance to current insecticides and antimalarial drugs there is a pressing need to discover and develop new agents that engage new targets in these organisms. To circumvent the effect of resistance to pyrethroid insecticides on the efficacy of insecticide treated nets (ITNs), the use of acetylcholinesterase (AChE) inhibitors on ITNs has drawn attention. In the first project, we explored a small library of γ- substituted oxoisoxazole- 2(3H)-carboxamides and isoxazol-3-yl carbamates, and nitriles as AChE inhibitors targeting wild- type (G3) and resistant (Akron) An. gambiae mosquito. In total 23 compounds were synthesized and evaluated. Both carbamates and carboximides with a 2-cyclopropylethyl side chain (1-87a and 1-88a) were extremely toxic to Akron mosquitos, yet these compounds did not exhibit appreciable selectivity between human and An. gambiae AChE. Unfortunately, none of the nitriles showed appreciable toxicity to G3 strain of the mosquitoes, nor did they inhibit An. gambiae AChE. In the second project, conducted in collaboration with Professor Michael Klemba, we focused on the mode of action of an established antimalarial drug, Mefloquine (MQ). Dr. Klemba's recently developed amino acid efflux assay was used to determine the effect of MQ and its open-ring analogs on hemoglobin endocytosis and catabolism in P. falciparum-infected erythrocytes. In total 26 MQ analogs were synthesized and 18 were studied in depth to determine their potency to inhibit leucine (Leu) efflux and parasite growth (SYBR Green). An excellent correlation (R² = 0.98) over nearly 4 log units was seen for these 18 compounds in the two assays. These data are consistent with the hypothesis that the antimalarial action of these compounds principally derives from inhibition of hemoglobin endocytosis. After this observation, a number of photo-affinity probes were designed and synthesized in hopes of isolating the molecular target of MQ. These analogs are currently being used by Dr. Klemba in pull-down experiments. In the third project, conducted in collaboration with Professor Belen Cassera, we sought to optimize a new antimalarial drug lead that would circumvent current resistance mechanisms. In Plasmodium parasites, the methylerythritol phosphate (MEP) pathway is known to be essential for its growth. This pathway is absent in humans, presenting the opportunity to develop potentially safe and effective therapeutic candidates. Previous work in the Cassera and Carlier lab had established that MMV008138 was the only compound in the Malaria Box that targeted the MEP pathway and that it was (1R,3S)-configured. My research expanded previous efforts in the Carlier group and produced synthesis of 73 analogs of MMV008138 (3-21a'1) that were tested for growth inhibition. These analogs featured variation at the A-, B-, C- and D-ring. In the process, a novel Pictet-Spengler ring expansion reaction of ortho-substituted acetphenones was discovered. The ring-expanded products were identified by means of 1D and 2D NMR experiments, HRMS, and X-ray crystallography. Among the 73 analogs prepared, four compounds showed similar growth inhibition potency to the lead 3-21a'1. In particular, the methoxyamide 3-80a, and the fluorinated A-ring analogs 3-124a, 3-124c and 3-124d all showed excellent (500-700 nM) growth IC₅₀ values against P. falciparum. All four showed full rescue upon co-application of IPP (200 μM), confirming that they target the MEP pathway. ADME-Tox evaluation of these new analogs will soon be underway.
Antiproliferative Compounds from Cleistanthus boivinianus from the Madagascar Dry Forest
Liu, Yixi; Young, Kelly; Rakotondraibe, L. Harinantenaina; Brodie, Peggy J.; Wiley, Jessica D.; Cassera, Maria B.; Callmander, Martin W.; Rakotondrajaona, R.; Rakotobe, Etienne; Rasamison, Vincent E.; TenDyke, Karen; Shen, Yongchun; Kingston, David G. I. (American Chemical Society, 2015-07-01)
Antiproliferative Natural Products from the Madagascar Rainforest
Hou, Yanpeng (Virginia Tech, 2009-09-09)
As part of an International Cooperative Biodiversity Groups (ICBG) program and a continuing search for anticancer natural products from the Madagascar rainforest, twenty extracts from Madagascar were selected for investigation based on their antiproliferative activity. Bioassay-guided fractionation of five of the extracts yielded sixteen new compounds, and their structures were determined using a combination of 1D and 2D NMR experiments, including COSY, HSQC/HMQC, HMBC, and ROESY/NOESY sequences, mass spectrometry, and chemical conversion. In addition, ten known compounds were obtained from five of the extracts. Studies on the remaining extracts were suspended due to various reasons. A multi-step synthesis of the sesquiterpenoid, (7R*)-opposite-4(15)-ene-1beta,7-diol, was also described. The first chapter of this dissertation reviews the new compounds isolated from Malagasy plants and marine organism in the last two decades. Chapters II to VI discuss the isolation, structure elucidation and bioactivities of new compounds from Scutia myrtina, Cordyla madagascariensis ssp. madagascariensis, Elaeodendron alluaudianum, Cassipourea lanceolata, and Sclerocarya birrea subsp. caffra. Chapter VII describes the synthesis and bioactivity of the sesquiterpenoid,(7R*)-opposite-4(15)-ene-1beta,7-diol. The isolation of known compounds is discussed briefly in the last chapter.
Antiproliferative Trihydroxyalkylcyclohexenones from Pleiogynium timoriense
Eaton, A. L.; Rakotondraibe, L. Harinantenaina; Brodie, P. J.; Goetz, M.; Kingston, David G. I. (American Chemical Society, 2015-07-01)
Antiproliferative triterpenoid saponins from Leptaulus citroides Baill. from the Madagascar rain forest
Su, Qingxi; Brodie, Peggy J.; Liu, Yixi; Miller, James S.; Andrianjafy, Naina M.; Antsiferana, Rabodo; Rasamison, Vincent E.; Kingston, David G. I. (Springer, 2016)
Bioassay-guided fractionation of EtOH extracts obtained from the roots and wood of the Madagascan plant Leptaulus citroides Baill. (Cardiopteridaceae) led to the isolation of ethyl esters of three new triterpenoid saponins (1–3) and the known sesquiterpenoid cinnamosmolide (4). The structures of 1–3 were elucidated by extensive 1D and 2D NMR experiments and mass spectrometry. Compounds 1, 2, and 4 showed moderate cytotoxicity against the A2780 human ovarian cancer cell line with IC50 values of 2.8, 10.2 and 2.0 lM, respectively.
Approaches to intermolecular structure elucidation utilizing NMR and DNP parameters
Tsiao, Candy (Virginia Polytechnic Institute and State University, 1989)
This thesis is divided into two parts. The first part involves the study of molecular structure utilizing Ianthanide induced shift (LIS) and lanthanide induced relaxation (LIR) nuclear magnetic resonance (NMR). It the course of these studies, it was found that the trifluoroethoxy group is a good deactivating group towards lanthanide shift reagents (LSR) and can be used to selectively deactivate multifunctional molecules. The second part of the thesis involves the utilization of liquid-liquid intermolecular transfer (LLIT) dynamic nuclear polarization (DNP) to study the microwave power needed to achieve saturation using deuterated and nondeuterated 2,4,6-tri-tert-butylphenoxy and galvinoxyl radicals, and ¹⁴N labelled, nondeuterated and ¹⁴N labelled, deuterated 4-hydroxy-TEMPO radicals. Also, selective ¹H DNP enhancements for taxol in solid-liquid intermolecular transfer (SLIT) DNP low-to-high field transfer experiments were obtained. Finally, the syntheses of compounds with both a LSR moiety and a nitroxide radical moiety in the same molecule were examined. LLIT DNP transfer experiments for the intramolecular LSR-nitroxide radicals molecular system and the intermolecular LSR—radicals systems were studied. Conclusions based on this study provide new insight regarding approaches for new LIS and DNP studies.
Approaches to the synthesis of modified taxols
Jitrangsri, Chote (Virginia Polytechnic Institute and State University, 1986)
Investigation on the synthesis of the C-13 side chain of taxol was carried out in order to prepare modified taxol derivatives by coupling of the side chain acid chloride to a suitably protected baccatin III. The side chain was prepared by the Darzens condensation. Acylation of baccatin III was performed with simple acylating agents and extensive studies of the ¹H NMR and ¹³C NMR spectra of various acylbaccatins III were carried out aided by homonuclear and heteronuclear COSY experiments. This work led to the unambiguous assignment of the ¹H NMR and ¹³C NMR spectra of these compounds. Coupling of more bulky side chains to 7-(2,2,2-trichloroethyloxycarbonyl) baccatin III was difficult and yields were poor. Conventional methods, using triethylamine or pyridine with 4-dimethylaminopyridine in the coupling reaction of 3- phenylpropanoyl chloride and 7-(2,2,2-trichloroethyloxycarbonyl) baccatin III led to the desired coupled product in low yield together with two coupled compounds possessing more than one phenylpropanoyl group on the C-13 side chain. When the coupling reaction was performed in the presence of silver cyanide in refluxing toluene, only 13-(3-phenylpropanoyl) baccatin III was obtained. However, these two methods were not successful in the coupling reaction of 2-acetyl-3- phenyllactyl chlorlde with 7-(2,2,2-trichloroethyloxycarbonyl) baccatin III. Preliminary studies on the cleavage of the N-acyl group at the C-3' position of taxol and cephalomannine were performed. Taxol reacted with zinc bromide in chloroform-methanol solution to produce 10- deacetyl-7-epitaxol and 10-deacetyltaxol. No cleavage of the N-acyl group was detected in this case and in other reactions in which taxol was treated with various selective reagents. Other attempts involved the conversion of cephalomannine to its ozonolysis products with a pyruvyl group at the 3’-NH group. A method of cleavage of the N-pyruvyl group has not yet been found, however.
Assessment of coal liquefaction behavior through product characterization with hyphenated chromatographic/spectroscopic methods
Hellgeth, John William (Virginia Polytechnic Institute and State University, 1986)
The understanding of liquefaction behaviors, related to a coal's properties and a recycle solvent's composition, is essential for the development of an efficient direct liquefaction process. In this dissertation, a study of the liquefaction behaviors of an Eastern us bituminous and four Western US subbituminous coals is presented. The experimental approach has been to examine their behaviors under various reaction conditions with in-house microautoclave reactor and Kerr McGee pilot plant liquefaction runs. In-house runs involved surveys of coal types and process solvent compositions with variations in reaction times, temperatures and atmospheres. Runs performed at Kerr McGee examined the use of tetrahydroquinoline (TBQ) as a process solvent with a Wyoming coal. Liquefaction activities were assessed through determinations of coal conversion to both solvent-soluble products and distillate yields. Per the in-house liquefaction studies, a novel microautoclave reactor design and product recovery methods were developed, evaluated and employed. The reaction chemistries of !n !!S!! metal species and basic nitrogen heterocycles were investigated specifically. Changes in trace element concentrations were ascertained by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) and Size Exclusion Chromatography/ICP-AES (SEC/ICP-AES). Pates of basic nitrogen components in distillate and solvent-soluble residuum products were examined by nitrogen mass balance determinations, Gas Chromatography/Pourier Transform Infrared Spectrometry (GC/PTIR) and Gas Chromatography/Mass Spectrometry (GC/MS). Conversions to soluble products demonstrated the expected dependencies of liquefaction on coal rank, elemental composition and petrography. The western subbituminous coals showed extreme sensitivity to drying and solvent-soaking pretreatments. Metal content analyses revealed that metals exist as complexed species in the liquefaction process. Higher conversions to toluene-soluble materials were obtained with THQ in contrast to other H-donor solvents. Adduction of THQ was significant in the non-distillate product stream, however. The direct coupling of Reversed Phase HPLC separations with PTIR (RP-HPLC/PTIR) detection through on-line, post-column extraction was developed. Though intended for application to coal-liquefied product (CLP) analysis, this system was evaluated rigorously for both chromatographic and spectral performance. Throughout this investigation, the overall utility of these hyphenated methods for CLP analysis was explored. These methods demonstrated exceptional performance in providing a wealth of qualitative and quantitative information in a rapid manner.
Biosynthesis of Caldariellaquinone in Sulfolobus acidocaldarius
Zhou, Dan (Virginia Tech, 1991)
The biosynthesis of caldariellaquinone (CQ) has been studied in Sulfolobus acidocaldarius using a variety of methods. By growing cells with a series of tyrosines labeled with deuterium or ¹³C and measuring the extent and position at which label was incorporated into the CQ by mass spectrometry, it was concluded that the benzo[b]thiophen-4,7-quinone ring of CQ is derived as an intact unit from all of the carbons of tyrosine except C-1. Additional work, using (3S)-L-(2-²H, 3-²H]-, (3R)-D-[2-²H, 3-²H]-, (3S)-D-[3-²H]-, and (3R)-L-[3-²H]- tyrosine, demonstrated that the pro-3S hydrogen of either D- or L-tyrosine is the origin of the C-3 proton of the benzo[b]thiophene ring. Considering the above information and the structure of CQ, it was concluded that CQ was most likely biosynthesized by the condensation of farnesylfarnesyl pyrophosphate with homogentisic acid (HA) in a reaction analogous to that found in the biosynthesis of ubiquinone. The possibility of this reaction being involved in the biosynthesis of CQ was supported by the identification of farnesylfarnesol, a hydrolytic breakdown product of farnesylfarnesyl pyrophosphate, by gas chromatography-mass spectrometry (GC-MS) of purified lipid extracts. The possible involvement of HA in CQ biosynthesis, however, could not be confirmed by five independent methods. The possible formation of CQ by the condensation of benzo[b]thiophen-4,7-quinone with farnesylfarnesyl pyrophosphate was eliminated by the inability to detect benzo[b]thiophen-4,7-quinone in S. acidocaldarius. Attempts to identify the tyrosine metabolites leading to CQ by studing the metabolisms of tyrosine, 2-fluorotyrosine, and 3-fluorotyrosine in S. acidocaldarius lead to the identification of two previously undescribed pathways for tyrosine metabolism. These two pathways branch after the conversion of tyrosine to 4-hydroxyphenylacetic acid (pHPA). The ability of labeled pDHPA to be incorporated into these metabolites, but not into CQ, indicates that the first committed step in the biosynthesis of CQ occurs at either tyrosine or a metabolite very closely related to tyrosine, e.g., 4-hydroxyphenylpyruvate (pHPP). Analysis of the extract of the cells grown with 3-fluorotyrosine showed two fluorine-containing compounds, which are likely to be fluoro-analogues of the intermediates in the biosynthesis of CQ. However, because of the small amount of these two compounds found (24 nmoles/g of wet weight), structural characterization was not possible. Both the methyl and sulfur groups of the methylthio portion of CQ were shown to arise from methionine. Mass spectral analysis of the CQ isolated from cells grown in the presence of [³⁴S-methyl-²H₃]-L-methionine clearly showed, however, that the methylthio group of CQ is not derived as an intact unit from the methylthio group of methionine. Additional work supported the theory that the methionine sulfur first undergoes transsulfuration to cysteine, which then supplies the sulfur for both the methylthio and the benzo[b]thiophene moieties of CQ. This represents the first example of transsulfuration from methionine to cysteine occurring in archaebacteria.
The biosynthesis of ravidomycin
Keyes, Robert F. (Virginia Tech, 1989-07-01)
Ravidomycin is a yellow antitumor antibiotic produced by Streptomyces ravidus. Ravidomycin shows strong antitumor activity against P388 lymphocytic leukemia, the colon 38 tumor, and the CD8Fl mammary tumor. It is also very active against Gram positive bacteria. Biosynthetic studies have shown that the aglycone unit comes from the folding of a polyketide chain with the vinyl unit arising from propionic acid. Since this vinyl functionality is believed to playa role in the antitumor activity of the antibiotic, it is of interest to elucidate the stereochemical selectivity in its formation from propionic acid. The synthesis of (R) and (S)-L2-²H₁ j propionate, incorporation of the labelled material, and chemical analysis of the resulting antibiotic was be used to determine the stereochemistry of formation of the vinyl side chain. It was found that propionate was incorporated with ravidomycin with stereospecific loss of the 2-(pro-R)-proton.

Browsing by Author "Kingston, David G. I."

Results Per Page

Sort Options