RESUMEN
A lanthanide-binding tag site-specifically attached to a protein presents a tool to probe the protein by multiple spectroscopic techniques, including nuclear magnetic resonance, electron paramagnetic resonance and time-resolved luminescence spectroscopy. Here a new stable chiral LnIII tag, referred to as C12, is presented for spontaneous and quantitative reaction with a cysteine residue to generate a stable thioether bond. The synthetic protocol of the tag is relatively straightforward, and the tag is stable for storage and shipping. It displays greatly enhanced reactivity towards selenocysteine, opening a route towards selective tagging of selenocysteine in proteins containing cysteine residues. Loaded with TbIII or TmIII ions, the C12 tag readily generates pseudocontact shifts (PCS) in protein NMR spectra. It produces a relatively rigid tether between lanthanide and protein, which is beneficial for interpretation of the PCSs by single magnetic susceptibility anisotropy tensors, and it is suitable for measuring distance distributions in double electron-electron resonance experiments. Upon reaction with cysteine or other thiol compounds, the TbIII complex exhibits a 100-fold enhancement in luminescence quantum yield, affording a highly sensitive turn-on luminescence probe for time-resolved FRET assays and enzyme reaction monitoring.
Asunto(s)
Elementos de la Serie de los Lantanoides , Cisteína , Luminiscencia , Resonancia Magnética Nuclear Biomolecular , ProteínasRESUMEN
We have established photochemical access to thietane or tetrahydrothiophene compounds from thiobenzophenone derivatives and acrylonitrile, wherein the product selectivity is controlled by a simple adjustment of the reagent concentration in solution. Small libraries of five-membered ring sulfur-containing compounds were prepared through a thia-Paternò-Büchi reaction, followed by a previously unknown regioselective photochemical ring enlargement reaction in a domino process or a stepwise fashion. A mechanism is proposed to rationalize this ring enlargement reaction via a carbene species provided from photoexcited thiocarbonyl compounds.
RESUMEN
Homo-oligomers of the natural product oxetin (cis-3-amino-2-oxetanecarboxylic acid) were prepared and their conformational behaviour studied in solution and solid state and by molecular modelling. The predominant secondary structure was a 10-helix, propiciously stabilized by a network of 5-membered ring H-bonds implicating ring oxygens and neighboring amide hydrogen atoms.
RESUMEN
A short synthesis of all four stereoisomers of 3-amino-2-oxetanecarboxylic acid (oxetin) is described. The oxetane core is built using a Paternò-Büchi photochemical [2 + 2] cycloaddition; from the key intermediates, complementary resolution protocols provide access to enantiomerically pure oxetin and epi-oxetin on gram-scale.