Synthesis of two 6-aza-uridines modified by benzoheterocycle as environmentally sensitive fluorescent nucleosides

Unveiling the impact of the fluorophore pyrrole, indole, furan, benzofuran, thiophene, benzothiophene, and pyrene attachments on the C7 atom of the isomorphic fluorescent thieno-guanine: A theoretical investigation

Thieno-guanine (thG) is a prominent emissive surrogate of natural guanine (G), which almost perfectly mimics G in nucleic duplexes. In this paper, to widen the utility of thG, the C7 attachment effects by aromatic pyrrole, indole, furan, benzofuran, thiophene, benzothiophene, and pyrene on the structural, electronic, and photophysical properties of thG were theoretically examined by using the density functional theory (DFT) and the time-dependent DFT (TD-DFT). Calculations were performed employing the hybrid B3LYP and the long-range corrected CAM-B3LYP density functionals in combination with the 6-311++G(d, p) basis set. Rigid scan calculations and optimizations were performed to obtain the most stable rotamers, and totally 14 bases (including thG) were studied. The hole-electron theory and the interfragment charge transfer (IFCT) method were applied to reveal the intrinsic characteristics of the low-lying electron excitation processes. In water solution, all the S1 states of the thG-derivatives are highly allowed ππ∗ states dominated by HOMO (L)→LUMO (L) with some charges (0.028-0.193 e) been transferred from the introduced groups to the thG-moiety. The introduced groups can tune the photophysics of thG resulting in improved fluorescent properties, including visible excitation and emission wavelengths, greater absorption and emission intensities (oscillator strengths), and larger Stokes shifts. In water solution, all substituents display fluorescence wavelength longer than 500 nm and the Stokes shifts are larger than 100 nm. Also examined are the effects of base pairing with cytosine (C), and it was revealed that the S1 states of all the studied base pairs (totally 14) are local excitations of the thG-derivatives. Both the S1 state excitation energies and the fluorescence wavelengths are red-shifted to some extent after base pair with C, with a concomitantly decrease of the corresponding oscillator strength.

Synthesis of Multifused Pyrrolo[1,2-a]quinoline Systems by Tandem Aza-Michael-Aldol Reactions and Their Application to Molecular Sensing Studies

Herein, we have presented a weak acid-promoted tandem aza-Michael-aldol strategy for the synthesis of diversely fused pyrrolo[1,2-a]quinoline (tricyclic to pentacyclic scaffolds) by the construction of both pyrrole and quinoline ring in one pot. The described protocol fabricated two C-N bonds and one C-C bond in the pyrrole-quinoline rings which have been sequentially formed under transition-metal-free conditions by the extrusion of eco-friendly water molecules. A ketorolac drug analogue has been synthesized following the current protocol, and one of the synthesized tricyclic pyrrolo[1,2-a]quinoline fluorophores has been used to detect highly toxic picric acid via the fluorescence quenching effect.

Rhodium(III)-Catalyzed Synthesis of Diverse Fluorescent Polycyclic Purinium Salts from 6-Arylpurine Nucleosides and Alkynes

Described herein is an efficient strategy for assembling a new library of functionalized polycyclic purinium salts with a wide range of anions through Rh^III-catalyzed C-H activation/annulation of 6-arylpurine nucleosides with alkynes under mild reaction conditions. The resulting products displayed tunable photoluminescence covering most of the visible spectrum. Mechanistic insights delineated the rhodium catalyst's mode of action. A purinoisoquinolinium-coordinated rhodium(I) sandwich complex was well characterized and identified as the key intermediate.