A pyrazolo[1,5-a]pyridine-based ratiometric fluorescent probe for sensing Cu2+ in cell

Ratiometric fluorescent probes based on FRET mechanism have attracted great attention due to their large pseudo-Stokes shifts and built-in correction for environmental effects. However, most donors failed to meet the requirement that the emission of the donor must overlap well with the absorption of the acceptor. Therefore, searching for new fluorophore to construct FRET system is in great need. In this paper, a new fluorescent dye pyrazolo[1,5-a]pyridine was synthesized and used as a donor in the FRET system for ratiometric sensing of Cu²⁺. The probe is based on FRET and PET mechanism. It shows high selectivity and sensitivity toward Cu²⁺ (detection limit 30 nM). Furthermore, it was successfully used to detect Cu²⁺ in Glioma cells.

A novel pyrazolo[1,5-a]pyridine fluorophore and its application to detect pH in cells

A new fluorescent probe based on pyrazolo[1,5-a]pyridine was synthesized and used to monitor the pH in cells. This probe exhibited a fast response to acidic pH (less than 10 s), a high quantum yield (φ = 0.64), and high selectivity and sensitivity. The response mechanism of the fluorescent probes relies on the ICT change.

Tandem Aza Michael Addition-Vinylogous Nitroaldol Condensation: Construction of Highly Substituted N-Fused 3-Nitropyrazolopyridines

A base-mediated tandem aza-Michael addition-vinylogous nitroaldol condensation has been described between 3,5-dialkyl 4-nitropyrazoles and alkynyl ketones/aldehydes. This transition metal-free atom economical transformation occurred via C-N and C═C bond formations in one step with the elimination of water. The construction of a variety of highly substituted N-fused 3-nitropyrazolopyridine derivatives has been demonstrated with good yields. Good to excellent regioselectivities have been achieved with unsymmetrically substituted 4-nitropyrazoles.

Synthesis of 7-cyanoindolizine derivatives via a tandem reaction

A series of 2-substituted and 2,3-disubstituted 5-cyanoindolizine derivatives were conveniently synthesized by a one-pot tandem reaction under mild conditions in moderate yields. The reaction mechanism was proposed.

The synthesis, characterization and optical properties of novel 2-acyl 6-arylindolizines

A series of novel 2-acyl-6-aryl substituted indolizine derivatives was synthesized by a novel tandem reaction between 4-acyl-pyrrole-2-carbaldehyde derivatives and ethyl 4-bromo-3-arylbut-2-enoate under mild conditions. The compounds were characterized using IR, (1)H NMR (13)C NMR and HRMS. The crystal structure of 7a was determined using single crystal X-ray crystallography. The absorption results showed that compounds 7a-e presented their absorption maxima at ca. 270 nm, while compounds 7f and 7g with a larger conjugation system exhibited red-shifted absorption character (ca. 280 nm). Fluorescence spectra revealed that these compounds exhibited blue fluorescence (434-456 nm) in dilute solutions and showed quantum yields of fluorescence between 0.02 and 0.39 in dichloromethane.

The synthesis, characterization and optical properties of novel 5-(3-aryl-1H-pyrazol-5-yl)-2-(3-butyl-1-chloroimidazo[1,5-a]pyridin-7-yl)-1,3,4-oxadiazole

A series of novel 5-(3-aryl-1H-pyrazol-5-yl)-2-(3-butyl-1-chloroimidazo[1,5-a]- pyridin-7-yl)-1,3,4-oxadiazole derivatives has been synthesized from 3-butyl-1-chloroimidazo[1,5-a]pyridine-7-carboxylic acid and ethyl 3-aryl-1H-pyrazole-5-carboxylate. The compounds were characterized using IR, (1)H NMR, HRMS and UV-vis absorption. The fluorescence spectral characteristics of the compounds in dichloromethane were investigated. The results showed that absorption λmax and emission λmax was less correlated with substituent groups on N-1 position of pyrazole moiety and para position of benzene moiety. The calculated molecular orbital correlates well with their absorption.

The optical properties, synthesis and characterization of novel 5-aryl-3-benzimidazolyl-1-phenyl-pyrazoline derivatives

A series of novel 5-aryl-3-benzimidazolyl-1-phenyl-pyrazoline derivatives were synthesized by the reaction of benzimidazolyl chalcone and phenylhydrazine in 41-72% yields. The compounds were characterized using IR, (1)H NMR and HRMS. Absorption and fluorescence spectra were measured in different organic solvent. An intense absorption maxima was noted at ca. 370 nm and emission maxima was noted at ca. 460 nm. The absorption spectra of the pyrazoline derivatives reveal that 5-aryl group attached to the pyrazoline ring hardly influenced the maximum absorption. The fluorescence spectra of these compounds indicated the emission wavelength was red shifted and the fluorescence intensity was decreased with the increase in solvent polarity.

Ethyl 2,4-dimethyl-pyrido[1,2-a]benz-imidazole-3-carboxyl-ate

The title compound, C₁₆H₁₆N₂O₂, was synthesized using a novel tandem annulation reaction between 1-(1H-benzo[d]imidazol-2-yl)ethanone and ethyl (E)-4-bromo­but-2-enoate under mild conditions. The dihedral angles formed by the mean plane of the five-membered imidazole ring with the dihydro­pyridin and benzene rings are 1.54 (9) and 1.85 (9)°, respectively.

Ethyl 2-benzoyl-6-methylindolizine-7-carboxylate

The title compound, C₁₉H₁₇NO₃, was synthesized using a tandem annulation reaction between 4-benzoyl-1H-pyrrole-2-carbaldehyde and (E)-ethyl 4-bromo­but-2-enoate under mild conditions. The dihedral angle between the benzene ring and the indolizine ring system is 41.73 (4)°.

Ethyl 3-{5-[(diethylamino)methyl]isoxazol-3-yl}-2-phenylpyrazolo[1,5-a]pyridine-5-carboxylate

In the title compound, C₂₄H₂₆N₄O₃, the pyrazolo[1,5-a]pyridine ring system makes dihedral angles of 38.130 (3) and 30.120 (3)°, respectively, with the isoxazole and phenyl rings. In the crystal, two mol­ecules are linked by a pair of C—H⋯N hydrogen bonds, forming a centrosymmetric dimer. A weak intra­molecular C—H⋯O inter­action is also present.