Allen Schoffstall - Academia.edu (original) (raw)

Papers by Allen Schoffstall

Origins Life Evol Biosphere, 1985

Journal of Organic Chemistry, 1989

The intramolecular nitrile oxide cycloaddition (INOC) of a series of unsaturated oximino ethers h... more The intramolecular nitrile oxide cycloaddition (INOC) of a series of unsaturated oximino ethers has been investigated. The synthesis of the olefinic nitrile oxides involves treating an unsaturated alcohol with a Î±-bromoalkanal O-(trimethylsilyl)oxime in the presence of fluoride ion followed by subsequent sodium hypochlorite oxidation. The nitrile oxides were not isolated but spontaneously underwent intramolecular cycloaddition to give fused five- and

Tetrahedron Letters, 1988

... NMR 11 (R 1 =Ph, R 2 =H, X=O) δ 3.15 (m, 1H), 3.60 (m, 2H), 3.96 (m, 2H), 4.40 (t, 1H, J=9.0 ... more ... NMR 11 (R 1 =Ph, R 2 =H, X=O) δ 3.15 (m, 1H), 3.60 (m, 2H), 3.96 (m, 2H), 4.40 (t, 1H, J=9.0 Hz), 4.50 (d, 1H, J=6.1 Hz), 5.22 (m, 1H) and 7.27.6 (m, 5H). R. Grigg, M. Jordan, A. Taugthongkum, FWB Einstein and T. Jones J. Chem. Soc. 47 (1984) Perkin Trans. I . ...

Origins of Life and Evolution of the Biosphere, 1985

ABSTRACT An objective of this work is to elucidate the mechanism of phosphorylation of nucleoside... more ABSTRACT An objective of this work is to elucidate the mechanism of phosphorylation of nucleosides in amide solvents and in urea. A second objective is to assess the importance of phosphorylation and dephosphorylation of nucleotide derivatives in amide environments. Although the most complex amide studied here was N-methylacetamide, inferences are made on the importance of dephosphorylation for nucleotides in oligopeptide environments.Phosphorylations in amide solvents and in urea are suggested to proceed through monomeric metaphosphate, which was first postulated as a reaction intermediate thirty years ago (Butcher and Westheimer, 1955). Phosphorylation of nucleosides and nucleotides and dephosphorylation of nucleotide derivatives have been studied in formamide, N-methylformamide, urea and N-methylacetamide. Hydrated forms of 5-ADP and 5ATP are unstable in hot amide solvents and in urea. They decompose to a mixture of adenosine and its phosphorylated derivatives. The rate of decomposition is much slower in N-methylacetamide than in formamide or urea. Experiments designed to prepare oligonucleotides in the presence of oligopeptides have been reported (White, 1983). According to the present study, it is not unreasonable to expect that nucleotide derivatives can be condensed with nucleosides to form oligonucleotides in a peptide environment. However, nucleotide monomers such as 5-ATP, 5-ADP or 5AMP will suffer isomerization or decomposition during condensation use of activated phosphate derivatives is preferable.Monomeric metaphosphate has not been isolated or characterized in amide solvents. It is proposed here as a reaction intermediate, probably in a complexed form with the amide.

Origins of Life, 1982

Nucleosides or deoxynucleosides were converted to a number of phosphorylated nucleotide and deoxy... more Nucleosides or deoxynucleosides were converted to a number of phosphorylated nucleotide and deoxynucleotide derivatives by ammonium of alkali dihydrogen phosphates in formamide. Conversions were smaller and slower at room temperature and greater and faster at elevated temperatures. Nucleotides afforded product mixtures to those obtained for nucleosides under the same conditions, indicating the occurrence of transphosphorylation processes. Products of the reaction at elevated temperatures were cyclic nucleotides, nucleoside monophosphates, nucleoside diphosphates and cyclic nucleotide phosphates. The relative amounts of products formed were quite temperature dependent. Cyclic nucleotides were found to be in greatest abundance for reactions run at 125 degree or above. Relative yields of 2&amp;#39;,3&amp;#39; and 5&amp;#39; nucleotides and 3&amp;#39; and 5&amp;#39; deoxynucleotides from several experiments are reported. 5&amp;#39;Monophosphates were generally found to be present in larger quantities than 2&amp;#39; or 3&amp;#39; monophosphates. 2&amp;#39;-Deoxyadenosine showed a preference for phosphorylation at the 3&amp;#39; position. Conclusion reached from mechanistic studies are that the phosphorylations are a series of equilibrium reactions, with cyclic nucleotides being formed irreversibly.

Origins of Life and Evolution of the Biosphere, 1986

We have proposed that phosphorylations in amide solvents might proceed through an intermediate mo... more We have proposed that phosphorylations in amide solvents might proceed through an intermediate monomeric metaphosphate (MMP) or a complex of MMP. I Recent work in other laboratories 2-4 suggests that a complex of MMP is a more likely possibility or that no intermediate is to be expected in amide media. Complexes of MMP have been detected for phosphorylations/dephosphorylations in aprotic solvents. 5 Results of kinetic studies of phosphorylations of alcohols in formamide will be reported. Reactions of amides with alcohols containing no phosphate will also be described. These reactions are considered as side reactions to phosphorylation rather than as reactions that lead to phosphorylation.

Origins of Life and Evolution of the Biosphere, 1988

Simple aliphatic alcohols, deoxynucleosides and nucleosides undergo reaction with formamide yield... more Simple aliphatic alcohols, deoxynucleosides and nucleosides undergo reaction with formamide yielding formate esters. Formate ester formation was observed to occur slowly at 100 °C and more rapidly at 130°C. As expected, formate esters were hydrolyzed to the alcohol and formic acid upon heating in aqueous solution. It was proposed to study the possibility that formate esters are formed initially in amide solvents, followed by displacement of formate by dihydrogen phosphate ion to form monophosphate esters. Experiments are described which demonstrate the formation and hydrolysis of formate esters, as well as their lack of reaction with hydrogen phosphate ion. Formate esters are not intermediates in the phosphorylation of nucleosides in formamide. Their formation has been observed and such an esterification is a side reaction during the phosphorylation of nucleosides in formamide.

The Journal of Organic Chemistry, 1989

ABSTRACT Reaction of the iminium salt derived from benzaldehyde oxime and (trimethylsilyl)methyl ... more ABSTRACT Reaction of the iminium salt derived from benzaldehyde oxime and (trimethylsilyl)methyl triflate with cesium fluoride gives rise to azomethine ylides. Dipolar cycloaddition proceeded with complete stereospecificity with dimethyl fumarate and maleate. In sharp contrast, reaction of the salt with alkynes produces dipolar cycloadducts derived from nitrones. The different products encountered result from the operation of several competing reactions which depend on the nature of the added dipolarophile. The initial step in all cases involves removal of the OH proton by cesium fluoride to give a nitrone intermediate. Cycloaddition occurs rapidly with activated alkynes to give isoxazolines. In the presence of the slower reacting alkene, a 1,3-silicon shift to the oxygen atom occurs, giving rise to an azomethine ylide intermediate, which subsequently cycloadds to the alkene. Supporting evidence for the postulated mechanism comes from the reaction of the iminium salt with sodium hydride and also by carrying out the cycloaddition in methanol.

J Org Chem, 1989

under argon, for 4 h. The mixture was cooled, concentrated in vacuo, and passed through a small c... more under argon, for 4 h. The mixture was cooled, concentrated in vacuo, and passed through a small column of basic alumina. The compound was eluted with ethyl acetate and then recrystallized from ethyl acetakpetroleum ether to give 209 mg (63%) of pure 38 as a light yellow crystal: mp 182-183 "C; 'H NMR 6 2.52 (3 H, CH,CO, s), 6.22 (1 H, Ha, m), 6.47 (1 H, Hg, dd), 7.06 (1 H, H7, d), 7.28-8.42 (18 H, m) (57,8 = 7.6) Hz, J8,g = 3.5 Hz, J8.10 = 1.5 Hz, Js,lo = 10 Hz); high-resolution mass spectrum mass obsd 552.1443, calcd 552.1572.

Journal of Chromatography A, 1983

Journal of Chemical Education, 1970

Journal of Chemical Education, 2011

ABSTRACT This undergraduate organic laboratory experiment consists of three different reactions o... more ABSTRACT This undergraduate organic laboratory experiment consists of three different reactions occurring in the same flask: a cycloaddition reaction, preceded by decarboxylation and nucleophilic substitution reactions. The decarboxylation and cycloaddition reactions occur using identical Cu(I) catalyst and conditions. Orange, lemon, and other citrus fruit peels and juices in the presence of CuSO4 lead to the Cu(I)-catalyzed decarboxylation of 3-phenyl-2-propynoic acid to give ethynylbenzene. These click chemistry conditions give Cu(I)-catalyzed azide–alkyne cycloaddition (CuAAC) of 2-azido-1-phenylethanone with ethynylbenzene to afford 1-phenyl-2-(4-phenyl-1H-1,2-3-triazol-1-yl)ethanone regioselectively.

Journal of Chemical Education, 2007

ABSTRACT Informed science educators who are responsible for undergraduate laboratory programs str... more ABSTRACT Informed science educators who are responsible for undergraduate laboratory programs strive to improve the effectiveness of learning in the laboratory. Guided-inquiry learning in the laboratory is one reasonable alternative (among others described here) to the verification approach to learning. Guided-inquiry learning offers students the opportunity to learn for themselves in a controlled laboratory environment where the instructor can handle the outcome and help guide students who are experiencing difficulty. Guided-inquiry experiments in organic chemistry have merit because they may help to improve understanding while increasing student interest. This paper presents the advantages and disadvantages of guided-inquiry experiments in organic chemistry. Several different types of guided-inquiry experiments in organic chemistry are summarized, together with the rationale for converting verification laboratory procedures to guided-inquiry experiments. Examples are given for enhancing guided-inquiry experiments to make the outcomes less predictable. Keywords (Audience): Second-Year Undergraduate

Journal of Chemical Education, 2012

An introductory, multidisciplinary lecture−laboratory course linked with a summer research experi... more An introductory, multidisciplinary lecture−laboratory course linked with a summer research experience has been established to provide undergraduate biology and chemistry majors with the skills needed to be successful in the research laboratory. This three-credit hour course was focused on laboratory skills and was designed to reinforce and develop the students' laboratory techniques and problemsolving skills, as well as to give encouragement to participate in a summer research project. This skills course consisted of a lecture section with team-based laboratory rotations of five-weeks each. Most students in the rotations had the opportunity to work in both biology and chemistry laboratories. The skills course culminated in several students being chosen to continue research in the summer with a research stipend while under the direction of one of the faculty mentors. The summer research projects were all collaborative efforts between chemists and biologists. Data are provided from voluntary entrance and exit student surveys to determine students' overall skill levels and interests before and after completion of the skills course. This course was valuable in encouraging students to become involved in and committed to research, for teaching them laboratory techniques, and for helping them evolve into independent researchers.

The Journal of Organic Chemistry, 1990

... 12) Cf.: Cook, A. G. In Enamines: Synthesis, Structure, and Reac-tions; Cook, A. G ... Albert... more ... 12) Cf.: Cook, A. G. In Enamines: Synthesis, Structure, and Reac-tions; Cook, A. G ... Albert Padwa,* Ugo Chiacchio,' Yves Garreau, Jamal M. Kassir, Keith E. Krumpe, and Allen M. Schoffstall Department of Chemistry, Emory University, Atlanta, Georgia 30322 Received November ...