Selective Selenol Fluorescent Probes: Design, Synthesis, Structural Determinants, and Biological Applications

Abstract

Selenium (Se) is an essential micronutrient element, and the biological significance of Se is predominantly dependent on its incorporation as selenocysteine (Sec), the genetically encoded 21st amino acid in protein synthesis, into the active site of selenoproteins, which have broad functions, ranging from redox regulation and anti-inflammation to the production of active thyroid hormones. Compared to its counterpart Cys, there are only limited probes for selective recognition of Sec, and such selectivity is strictly restricted at low pH conditions. We reported herein the design, synthesis, and biological evaluations of a series of potential Sec probes based on the mechanism of nucleophilic aromatic substitution. After the initial screening, the structural determinants for selective recognition of Sec were recapitulated. The follow-up studies identified that probe 19 (Sel-green) responds to Sec and other selenols with more than 100-fold increase of emission in neutral aqueous solution (pH 7.4), while there is no significant interference from the biological thiols, amines, or alcohols. Sel-green was successfully applied to quantify the Sec content in the selenoenzyme thioredoxin reductase and image endogenous Sec in live HepG2 cells. With the aid of Sel-green, we further demonstrated that the cytotoxicity of different selenocompounds is correlated to their ability metabolizing to selenols in cells. To the best of our knowledge, Sel-green is the first selenol probe that works under physiological conditions. The elucidation of the structure-activity relationship for selective recognition of selenols paves the way for further design of novel probes to better understand the pivotal role of Sec as well as selenoproteins in vivo.

Synthesis of Piperlongumine Analogues and Discovery of Nuclear Factor Erythroid 2-Related Factor 2 (Nrf2) Activators as Potential Neuroprotective Agents

“…However, the high cytotoxicity of PL hinders its application as a cytoprotective agent. 21 As our continued interests in discovering and developing novel redox active small molecules as potential therapeutic or diagnostic agents, 30,32,34,[44][45][46][47] we described the synthesis of PL and its analogues, and the discovery of two potent compounds (4 and 5) as potential neuroprotective agents to rescue the H 2 O 2 -or 6-OHDA-induced PC12 cell damage. Compared to the cytotoxicity data of 4 (a compound lacking the M2 moiety), PL shows greater toxic to both L02 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 13 cells and PC12 cells.…”

A specific fluorescent probe reveals compromised activity of methionine sulfoxide reductases in Parkinson's disease

“…Therefore, the past years have witnessed an increase in the number of studies that focus on developing diverse fluorescent probes for studying various protein activities 16–27 as well as small biomolecule functions. 28–35 One of the outstanding and well-recognized strategies in designing fluorescent probes is the manipulation of the intramolecular charge transfer (ICT) process, as the alteration of such a process is usually accompanied with a pronounced change in the absorbance/fluorescence profiles of a molecule, which forms the basis of the fluorescence sensing. Manipulation of the ICT process could be easily achieved by tuning the electronic character of the substituents attached to a fluorophore by exchanging electron donating groups with electron withdrawing groups or vice versa .…”

Brevetoxin-2, is a unique inhibitor of the C-terminal redox center of mammalian thioredoxin reductase-1

“…The selenol selective probe, Sel-green was prepared as previously reported 23 to monitor for Sec in the presence and absence of PbTx-2. The Sel-green probe undergoes a nucleophilic aromatic substitution (S N Ar) reaction selectively with selenols to release a fluorescent coumarin reporter (Scheme 1).…”

“…23 Rat TrxR (6 μM) and NADPH (0.1 mM) were incubated for 30 min in 45 mM Tris base, 0.9 mM EDTA. 0.5 M NaCl, 0.1 % glycerol, pH 7.…”