Enantioselective synthesis of 3-arylquinazolin-4(3H)-ones via peptide-catalyzed atroposelective bromination.

We report the development of a tertiary amine-containing β-turn peptide that catalyzes the atroposelective bromination of pharmaceutically relevant 3-arylquinazolin-4(3H)-ones (quinazolinones) with high levels of enantioinduction over a broad substrate scope. The structure of the free catalyst and the peptide-substrate complex were explored using X-ray crystallography and 2D-NOESY experiments. Quinazolinone rotational barriers about the chiral anilide axis were also studied using density functional theory calculations and are discussed in light of the high enantioselectivities observed.

NH+-F hydrogen bonding in a fluorinated "proton sponge" derivative: integration of solution, solid-state, gas-phase, and computational studies.

We report detailed studies on the characterization of an intramolecular NH-F hydrogen bond formed within a fluorinated "proton sponge" derivative. An ammonium ion, generated from 8-fluoro-N,N-dimethylnaphthalen-1-amine, serves as a charged hydrogen bond donor to a covalently bound fluorine appropriately positioned on the naphthalene skeleton. Potentiometric titrations of various N,N-dimethylnaphthalen-1-amines demonstrate a significant increase in basicity when hydrogen bonding is possible.

Reactive landing of gas-phase ions as a tool for the fabrication of metal oxide surfaces for in situ phosphopeptide enrichment.

Zirconium, titanium, and hafnium oxide-coated stainless steel surfaces are fabricated by reactive landing of gas-phase ions produced by electrospray ionization of group IVB metal alkoxides. The surfaces are used for in situ enrichment of phosphopeptides before analysis by matrix-assisted laser desorption ionization (MALDI) mass spectrometry. To evaluate this method we characterized ZrO(2) (zirconia) surfaces by (1) comparison with the other group IVB metal oxides of TiO(2) (titania) and HfO(2) (hafnia), (2) morphological characterization by SEM image analysis, and (3) dependence of phosphopeptide enrichment on the metal oxide layer thickness.

Matrix-free laser desorption/ionization of ions landed on plasma-treated metal surfaces.

We report new experiments in which laser desorption/ionization time-of-flight mass spectrometry (LDI-TOF-MS) was applied to detection and characterization of gramicidin S and IgG pentapeptide (DSDPR) that were reactively landed on plasma-treated stainless steel surfaces. The distributions of [M+H](+), [M+Na](+) and [M + K](+) ion species in LDI-TOF for gramicidin S and IgG pentapeptide (DSDPR) were found to be markedly different from those in conventional MALDI-TOF spectra of the same samples. LDI-TOF mass spectra showed a strong preference for [M+K](+) adducts even in the presence of a large excess of sodium cations, or following surface treatment with trifluoroacetic acid.