Fluorescence Properties of 5-(5,6-Dimethoxybenzothiazol-2-yl)-2′-deoxyuridine (dbtU) and Oligodeoxyribonucleotides Containing dbtU

Synthesis of fluorescent 5-heteroarylpyrimidine-containing oligonucleotides via post-synthetic trifluoromethyl conversion

Post-synthetic conversion of the trifluoromethyl group to a heteroaryl group at the C5 position of the pyrimidine base in DNA oligonucleotides was achieved. Specifically, the oligonucleotides containing 5-trifluoromethylpyrimidine bases were treated with o-phenylenediamines and o-aminothiophenols as nucleophiles to afford the corresponding 5-(benzimidazol-2-yl)- and 5-(benzothiazol-2-yl)-pyrimidine-modified bases. Furthermore, evaluation of the fluorescence properties of the obtained oligonucleotides revealed that among them the oligonucleotide containing 5-(5-methylbenzimidazol-2-yl)cytosine exhibited the highest fluorescence intensity. These results indicated that post-synthetic trifluoromethyl conversion, which is practical and operationally simple, is a powerful tool for exploring functional oligonucleotides.

Electrochemical Synthesis of Phenothiazinone as Fluorophore and Its Application in Bioimaging

Phenothiazinone is a promising yet underutilized fluorophore, possibly due to the lack of a general accessibility. This study reports a robust and scalable TEMPO-mediated electrochemical method to access a variety of phenothiazinones from 2-aminothiophenols and quinones. The electrosynthesis proceeds in a simple cell architecture under mild condition, and notably carbon-halogen bond in quinones remains compared to conventional methods, enabling orthogonal downstream functionalization. Mechanistic studies corroborate that TEMPO exerts a protective effect in avoiding product decomposition at the cathode. In particular, benzophenothiazinones show intriguing luminescence in both solid and solution state, and thus their photophysical properties are scrutinized in detail. Further bio-imaging of the lipid droplets in living cells highlights the considerable promise of benzophenothiazinones as fluorescent dye in the biomedical fields.

Continuous Flow Synthesis of 1,4-Benzothiazines Using Ambivalent Reactivity of (E)-β-Chlorovinyl Ketones: A Point of Reaction Control Enabled by Flow Chemistry

A continuous flow system to 1,4-benzothiazines was developed using the point of reaction control, where the ambivalent (E)-β-chlorovinyl ketones and 2,2'-dithiodianilines were confined in a diffusion controlled flow setting. The successful segregation of reactive chemical species in a flow setting allowed more defined reaction pathways that are not feasible in traditional batch reaction conditions. The point of reaction control in flow systems helps to execute the reactions often plagued with the concurrent generation of multiple chemical species.

Discovery of Novel Small-Molecule Antiangiogenesis Agents to Treat Diabetic Retinopathy

Diabetic retinopathy is the leading cause of blindness which is associated with excessive angiogenesis. Using the structure of wondonin marine natural products, we previously created a scaffold to develop a novel type of antiangiogenesis agent that possesses minimized cytotoxicity. To overcome its poor pharmaceutical properties, we further modified the structure. A new scaffold was derived in which the stereogenic carbon was changed to nitrogen and the 1,2,3-triazole ring was replaced by an alkyl chain. By comparing the bioactivity versus cytotoxicity, compound 31 was selected, which has improved aqueous solubility and an enhanced selectivity index. Mechanistically, 31 suppressed angiopoietin-2 (ANGPT2) expression induced by high glucose in retinal cells and exhibited in vivo antiangiogenic activity in choroidal neovascularization and oxygen-induced retinopathy mouse models. These results suggest the potential of 31 as a lead to develop antiangiogenic small-molecule drugs to treat diabetic retinopathy and as a chemical tool to elucidate new mechanisms of angiogenesis.

Highly Selective Y4 Receptor Antagonist Binds in an Allosteric Binding Pocket

Human neuropeptide Y receptors (Y₁R, Y₂R, Y₄R, and Y₅R) belong to the superfamily of G protein-coupled receptors and play an important role in the regulation of food intake and energy metabolism. We identified and characterized the first selective Y₄R allosteric antagonist (S)-VU0637120, an important step toward validating Y receptors as therapeutic targets for metabolic diseases. To obtain insight into the antagonistic mechanism of (S)-VU0637120, we conducted a variety of in vitro, ex vivo, and in silico studies. These studies revealed that (S)-VU0637120 selectively inhibits native Y₄R function and binds in an allosteric site located below the binding pocket of the endogenous ligand pancreatic polypeptide in the core of the Y₄R transmembrane domains. Taken together, our studies provide a first-of-its-kind tool for probing Y₄R function and improve the general understanding of allosteric modulation, ultimately contributing to the rational development of allosteric modulators for peptide-activated G protein-coupled receptors (GPCRs).

Synthesis and evaluation of 6-(11C-methyl(4-(pyridin-2-yl)thiazol-2-yl)amino)benzo[d]thiazol-2(3H)-one for imaging γ-8 dependent transmembrane AMPA receptor regulatory protein by PET

Transmembrane AMPA receptor regulatory proteins (TARPs) are a recently discovered family of proteins that modulate AMPA receptors activity. Based on a potent and selective TARP subtype γ-8 antagonist, 6-(methyl(4-(pyridin-2-yl)thiazol-2-yl)amino)benzo[d]thiazol-2(3H)-one (compound 9), we perform the radiosynthesis of its ¹¹C-isotopologue 1 and conduct preliminary PET evaluation to test the feasibility of imaging TARP γ-8 dependent receptors in vivo.

Benzo[4,5]thiazolo[3,2- c][1,3,5,2]oxadiazaborinines: Synthesis, Structural, and Photophysical Properties

A family of highly emissive benzo[4,5]thiazolo[3,2- c][1,3,5,2]oxadiazaborinines, conjugated with the donor 4-dimethylaminophenyl group, was designed and synthesized. Their photophysical, both in solution and in the solid state, and structural properties were investigated. The influence of donor and acceptor substituents (R) in the benzothiazole unit on photophysical properties of complexes was found out. The tetrafluorobenzothiazole analogue exhibits nonbonded nuclear spin-spin coupling between fluorines from the BF₂ group and α-fluorine atom at the benzene ring. Additionally, this boron complex demonstrates a comparatively high solid-state fluorescence quantum yield (Φ = 0.34).

Fluorescent Wittig reagent as a novel ratiometric probe for the quantification of 5-formyluracil and its application in cell imaging

For the first time a Wittig reagent was introduced into the design of a fluorescent probe for the quantification of 5-formyluracil.

Fluorogenic Labeling of 5-Formylpyrimidine Nucleotides in DNA and RNA

5-Formylcytosine (5fC) and 5-formyluracil (5fU) are natural nucleobase modifications that are generated by oxidative modification of 5-methylcytosine and thymine (or 5-methyluracil). Herein, we describe chemoselective labeling of 5-formylpyrimidine nucleotides in DNA and RNA by fluorogenic aldol-type condensation reactions with 2,3,3-trimethylindole derivatives. Mild and specific reaction conditions were developed for 5fU and 5fC to produce hemicyanine-like chromophores with distinct photophysical properties. Residue-specific detection was established by fluorescence readout as well as primer-extension assays. The reactions were optimized on DNA oligonucleotides and were equally suitable for the modification of 5fU- and 5fC-modified RNA. This direct labeling approach of 5-formylpyrimidines is expected to help in elucidating the occurrence, enzymatic transformations, and functional roles of these epigenetic/epitranscriptomic nucleobase modifications in DNA and RNA.

Controlling the fluorescence of benzofuran-modified uracil residues in oligonucleotides by triple-helix formation

We developed fluorescent turn-on probes containing a fluorescent nucleoside, 5-(benzofuran-2-yl)deoxyuridine (dU(BF)) or 5-(3-methylbenzofuran-2-yl)deoxyuridine (dU(MBF)), for the detection of single-stranded DNA or RNA by utilizing DNA triplex formation. Fluorescence measurements revealed that the probe containing dU(MBF) achieved superior fluorescence enhancement than that containing dU(BF). NMR and fluorescence analyses indicated that the fluorescence intensity increased upon triplex formation partly as a consequence of a conformational change at the bond between the 3-methylbenzofuran and uracil rings. In addition, it is suggested that the microenvironment around the 3-methylbenzofuran ring contributed to the fluorescence enhancement. Further, we developed a method for detecting RNA by rolling circular amplification in combination with triplex-induced fluorescence enhancement of the oligonucleotide probe containing dU(MBF).

[Development of selective detection method for 5-formyl-2'-deoxyuridine in DNA using a fluorogenic reagent]

It is important that various lesions in DNA were detected selectively and conveniently to know mechanisms of carcinogenicity and/or aging of cells. However, most detection methods of DNA lesion are complicated and take a long time for enzymatic hydrolysis and analysis by HPLC and/or mass spectrometry. This review shows the new concept for detection of DNA lesion by "fluorogenic reagent". Inspired by the unique bis-heteroaryl structure of luciferin and 5-heteroaryl-2'-deoxyuridine having good fluorescence properties, we designed and synthesized fluorogenic reagent 4,5-dimethoxy-2-aminothiophenol for a selective and convenient detection for 5-formyl-2'-deoxyuridine, which is generated in yields comparable to that of 2'-deoxy-8-oxoguanosine, in DNA. Generated 5-(5,6-dimethoxybenzothiazol-2-yl)-2'-deoxyuridine has a high quantum yield and larger Stokes shift in aqueous solution. This derivatization of 5-formyl-2'-deoxyuridine in oligodeoxynucleotide occurred quickly and quantitatively. The fluorogenic reagent was also revealed to detect 5-formyl-2'-deoxyuridine in γ-irradiated calf thymus DNA with irradiation dose dependent manner. Thus, our fluorogenic strategy enables to selective and convenient detection of lesion in DNA exposed to various forms of oxidative stress.