Synthesis of Soai Aldehydes for Asymmetric Autocatalysis by Desulfurative Cross-Coupling

Palladium-catalyzed dehydrosulfurative Liebes­kind–Srogl coupling of terminal alkynes with 2-mercapto-1,3-pyrimidine-5-carbaldehyde under base-free conditions provides 2-(alkynyl)-1,3-pyrimidine-5-carbaldehydes, which are substrates for autocatalytic amplification of chirality according to Soai et al. The mercapto aldehyde acceptor is obtained by condensation of Arnold’s vinamidinium salt with thiourea

Oxyluciferin Derivatives: A Toolbox of Environment-Sensitive Fluorescence Probes for Molecular and Cellular Applications

In this work, we used firefly oxyluciferin (<b>OxyLH</b>_<b>2</b>) and its polarity-dependent fluorescence mechanism as a sensitive tool to monitor biomolecular interactions. The chromophores, <b>OxyLH</b>_<b>2</b>, and its two analogues, <b>4-MeOxyLH</b> and <b>4,6′-DMeOxyL</b>, were modified trough carboxylic functionalization and then coupled to the N-terminus part of Tat and NCp7 peptides of human immunodeficiency virus type-1 (HIV-1). The photophysical properties of the labeled peptides were studied in live cells as well as in complex with different oligonucleotides in solution. By monitoring the emission properties of these derivatives we were able, for the first time, to study <i>in vitro</i> biomolecular interactions using oxyluciferin as a sensor. As an additional application, cyclopropyl-oxyluciferin (<b>5,5-Cpr-OxyLH</b>) was site-specifically conjugated to the thiol group (Cys-232) of the human protein α-1 antytripsin to investigate its interaction with porcine pancreatic elastase. Our data demonstrate that <b>OxyLH</b>_<b>2</b> and its derivatives can be used as fluorescence reporters for monitoring biomolecular interactions

Bioinspired Molecular Lantern: Tuning the Firefly Oxyluciferin Emission with Host–Guest Chemistry

Fireflies generate flashes of visible light via luciferase-catalyzed chemiexcitation of the substrate (luciferin) to the first excited state of the emitter (oxyluciferin). Microenvironment effects are often invoked to explain the effects of the luciferase active pocket on the emission; however, the exceedingly complex spectrochemistry and synthetic burdens have precluded elucidation of the nature of these interactions. To decipher the effects of microenvironment on the light emission, here the hydrophobic interior of cucurbit[7]­uril (CB7) is used to mimic the nonpolar active pocket of luciferase. The hydrophobic interior of CB7 induces shifts of the ground-state p<i>K</i>_as by 1.9–2.5 units to higher values. Upon sequestration, the emission maxima of neutral firefly oxyluciferin and its conjugate monodeprotonated base are blue-shifted by 40 and 39 nm, respectively, resulting in visual color changes of the emitted light

On the Influence of Water on the Electronic Structure of Firefly Oxyluciferin Anions from Absorption Spectroscopy of Bare and Monohydrated Ions in Vacuo

A complete understanding of the physics underlying the varied colors of firefly bioluminescence remains elusive because it is difficult to disentangle different enzyme–lumophore interactions. Experiments on isolated ions are useful to establish a proper reference when there are no microenvironmental perturbations. Here, we use action spectroscopy to compare the absorption by the firefly oxyluciferin lumophore isolated in vacuo and complexed with a single water molecule. While the process relevant to bioluminescence within the luciferase cavity is light emission, the absorption data presented here provide a unique insight into how the electronic states of oxyluciferin are altered by microenvironmental perturbations. For the bare ion we observe broad absorption with a maximum at 548 ± 10 nm, and addition of a water molecule is found to blue-shift the absorption by approximately 50 nm (0.23 eV). Test calculations at various levels of theory uniformly predict a blue-shift in absorption caused by a single water molecule, but are only qualitatively in agreement with experiment highlighting limitations in what can be expected from methods commonly used in studies on oxyluciferin. Combined molecular dynamics simulations and time-dependent density functional theory calculations closely reproduce the broad experimental peaks and also indicate that the preferred binding site for the water molecule is the phenolate oxygen of the anion. Predicting the effects of microenvironmental interactions on the electronic structure of the oxyluciferin anion with high accuracy is a nontrivial task for theory, and our experimental results therefore serve as important benchmarks for future calculations