Publications by authors named "Mark Spell"

5 Publications

  • Page 1 of 1

A Visible-Light-Promoted O-Glycosylation with a Thioglycoside Donor.

Angew Chem Int Ed Engl 2016 05 18;55(22):6515-9. Epub 2016 Apr 18.

Department of Chemistry, Louisiana State University, 232 Choppin Hall, Baton Rouge, LA, 70803, USA.

Visible-light irradiation of 4-p-methoxyphenyl-3-butenylthioglucoside donors in the presence of Umemoto's reagent and alcohol acceptors serves as a mild approach to O-glycosylation. Visible-light photocatalysts are not required for activation, and alkyl- and arylthioglycosides not bearing the p-methoxystyrene are inert to these conditions. Experimental and computational evidence for an intervening electron donor-acceptor complex, which is necessary for reactivity, is provided. Yields with primary, secondary, and tertiary alcohol acceptors range from moderate to high. Complete β-selectivity can be attained through neighboring-group participation.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/anie.201601566DOI Listing
May 2016

Remote Hydroxylation through Radical Translocation and Polar Crossover.

Angew Chem Int Ed Engl 2015 Jun 26;54(27):7837-41. Epub 2015 May 26.

Department of Chemistry, Louisiana State University, 232 Choppin Hall, Baton Rouge, LA 70803 (USA).

Mild conditions are reported for the hydroxylation of aliphatic C-H bonds through radical translocation, oxidation to carbocation, and nucleophilic trapping with H2O. This remote functionalization employs fac-[Ir(ppy)3] together with Tz(o) sulfonate esters and sulfonamides to facilitate the site-selective replacement of relatively inert C-H bonds with the more synthetically useful C-OH group. The hydroxylation of a range of substrates and the methoxylation of two substrates through 1,6- and 1,7-hydrogen-atom transfer are demonstrated. In addition, a synthesis of the antidepressant fluoxetine using remote hydroxylation as a key step is presented.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/anie.201500880DOI Listing
June 2015

Magnetic and structural properties of dinuclear singly bridged-phenoxido metal(II) complexes.

Dalton Trans 2015 Feb;44(5):2110-21

Department of Chemistry, University of Louisiana at Lafayette, Lafayette, LA 70504, USA.

The reaction of a methanolic solution containing the bi-compartmental phenolic ligand 2,6-bis[bis(2-pyridylmethyl)aminomethyl]-4-chlorophenol (L(Cl)-OH) with MCl2·nH2O in the presence of NH4PF6 or NaClO4 afforded the dinuclear bridged-phenoxido dichlorido-metal(ii) complexes [Co2(μ-L(Cl)O)(H2O)2Cl2][Co2(μ-L(Cl)O)(MeOH)2Cl2](PF6)2 (), [Ni2(μ-L(Cl)O)(MeOH)2Cl2]PF6 (), [Ni2(μ-L(Cl)O)(MeOH)(H2O)Cl2]ClO4·1.25H2O (), [Cu2(μ-L(Cl)O)Cl2]PF6·1/2MeOH () and [Zn2(μ-L(Cl)O)Cl2]PF6·MeOH (). The complexes were characterized by elemental microanalyses, conductivity measurements, IR and UV-Vis spectroscopy, mass spectrometry and single crystal X-ray crystallography. Each M(ii) center within the dinuclear complex cations is octahedrally coordinated in complexes , and five-coordinated distorted square pyramidal in and . Magnetic susceptibility measurements at variable temperature of the complexes revealed weak to moderate antiferromagnetic coupling with |J| values = 8.38, 39.0, 30.2 and 0.79 cm(-1), respectively. The results of DFT calculations correlate well with the experimentally determined antiferromagnetic coupling and show that the magnetic exchange coupling occurs mainly through the phenoxido bridge M-O-M. Implications of geometry around the central metal ion, MM distance, M-O-M bond angle and overlapping of magnetic orbitals on the magnetic exchange coupling are discussed.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c4dt03508aDOI Listing
February 2015

Ascaroside activity in Caenorhabditis elegans is highly dependent on chemical structure.

Bioorg Med Chem 2013 Sep 18;21(18):5754-69. Epub 2013 Jul 18.

Department of Chemistry, Louisiana State University, Baton Rouge, 70803, United States.

The nematode Caenorhabditis elegans secretes ascarosides, structurally diverse derivatives of the 3,6-dideoxysugar ascarylose, and uses them in chemical communication. At high population densities, specific ascarosides, which are together known as the dauer pheromone, trigger entry into the stress-resistant dauer larval stage. In order to study the structure-activity relationships for the ascarosides, we synthesized a panel of ascarosides and tested them for dauer-inducing activity. This panel includes a number of natural ascarosides that were detected in crude pheromone extract, but as yet have no assigned function, as well as many unnatural ascaroside derivatives. Most of these ascarosides, some of which have significant structural similarity to the natural dauer pheromone components, have very little dauer-inducing activity. Our results provide a primer to ascaroside structure-activity relationships and suggest that slight modifications to ascaroside structure dramatically influence binding to the relevant G protein-coupled receptors that control dauer formation.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.bmc.2013.07.018DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4469380PMC
September 2013

An α-selective, visible light photocatalytic glycosylation of alcohols with selenoglycosides.

Carbohydr Res 2013 Mar 16;369:42-7. Epub 2013 Jan 16.

Department of Chemistry, Louisiana State University, 232 Choppin Hall, Baton Rouge, LA 70803, United States.

Exceptionally mild procedures for the visible light photocatalytic activation of selenoglycoside donors in the presence of alcohol acceptors have been developed. This process is demonstrated with both 1-phenylselenyl-2,3,4,6-tetra-O-benzyl glucoside (1) and 1-phenylselenyl-2,3,4,6-tetra-O-benzyl galactoside (2). Catalysis is effected with both metal (Ru(bpy)3) and organocatalysts (diphenyldiselenide). Reactions afford, in all cases, primarily the α-anomers with selectivities that vary with solvent. This represents the first example of a visible light-promoted O-glycosylation.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.carres.2013.01.004DOI Listing
March 2013
-->