Artificial Host Molecules to Covalently Capture 8-Nitro-cGMP in Neutral Aqueous Solutions and in Cells

New 1,3-diazaphenoxazine derivatives (nitroG-Grasp-Guanidine, NGG) have been developed to covalently capture 8-nitro-cGMP in neutral aqueous solutions, which furnish a thiol reactive group to displace the 8-nitro group and a guanidine unit for interaction with the cyclic phosphate. The thiol group was introduced to the 1,3-diazaphenoxazine skeleton through a 2-aminobenzylthiol group (NGG-H) and its 4-methyl (NGG-pMe) and 6-methyl (NGG-oMe) substituted derivatives. The covalent adducts were formed between the NGG derivatives and 8-nitro-cGMP in neutral aqueous solutions. Among the NGG derivatives, the one with the 6-methyl group (NGG-oMe) exhibited the most efficient capture reaction. Furthermore, NGG-H showed a cell permeability into HEK-293 and RAW 264.7 cells and reduced the intracellular 8-nitro-cGMP level. The NGG derivatives developed in this study would become a valuable tool to study the intracellular role of 8-nitro-cGMP.

Antiviral activity spectrum of phenoxazine nucleoside derivatives

The phenoxazine scaffold is widely used to stabilize nucleic acid duplexes, as a part of fluorescent probes for the study of nucleic acid structure, recognition, and metabolism, etc. Here we present the synthesis of phenoxazine-based nucleoside derivatives and their antiviral activity against a panel of structurally diverse viruses: enveloped DNA herpesviruses varicella zoster virus (VZV) and human cytomegalovirus, enveloped RNA tick-borne encephalitis virus (TBEV), and non-enveloped RNA enteroviruses. Studied compounds were effective against DNA and RNA viruses reproduction in cell culture. 3-(2'-Deoxy-β-D-ribofuranosyl)-1,3-diaza-2-oxophenoxazine proved to be a potent inhibitor of VZV replication with superior activity against wild type than thymidine kinase deficient strains (EC₅₀ 0.06 and 10 μM, respectively). This compound did not show cytotoxicity on all the studied cell lines. Several compounds showed promising activity against TBEV (EC₅₀ 0.35-0.91 μM), but the activity was accompanied by pronounced cytotoxicity. These compounds may be considered as a good starting point for further structure optimization as antiherpesviral or antiflaviviral compounds.

Luminescent europium sensors for specific detection of 8-oxo-dGTP by time-gated fluorescence

The 9-hydroxy-1,3-diazaphenoxazine-2-one unit was conjugated with the Eu³⁺-cyclen complex through a linker. This diazaphenoxazine group was expected as an antenna unit for the excitation of europium ion, and a selective recognition site for 8-oxo-dGTP base. Among the synthesized three derivatives, the highest fluorescence emission was obtained by the complex constructed of an ethylene linker and the cyclen unit with three N,N-dimethylacetamide groups. The Eu³⁺-cyclen complex exhibited a selective response to the 8-oxo-dGTP in aqueous media by a time-resolved fluorescence assay.

Synthetic receptor molecules for selective fluorescence detection of 8-oxo-dGTP in aqueous media

A series of 9-hydroxy-1,3-diazaphenoxazine-2-one derivatives were synthesized as fluorescent receptor molecules for 8-oxo-dGTP, which attach the cyclen-zinc complex at the 3-N position as the binding site for the triphosphate and the (2-aryloxycarbonylamino)ethyl group at the 9-O position as the hydrogen bonding site for 8-oxoguanine. Among these molecules, the receptor molecule 5a-Zn constructed of the ethyl linker at 3-N and the (2-benzyloxycarbonyl amino)ethyl group at 9-O displayed the best recognition ability for 8-oxoguanosine triphosphate (8-oxo-dGTP) in aqueous media. The receptor 5a-Zn was also shown to selectively detect 8-oxo-dGTP in a cell lysate solution.

Synthesis of oligonucleotides containing novel G-clamp analogue with C8-tethered group in phenoxazine ring: Implication to qPCR detection of the low-copy Kemerovo virus dsRNA

Nowadays modified oligonucleotides are widely used in diagnostics and as novel therapeutics. Introduction of modified or unnatural residues into oligonucleotides allows fine tuning of their binding properties to complementary nucleic acids and leads to improved stability both in vitro and in vivo. Previously it was demonstrated that insertion of phenoxazine nucleotides with various groups in C9-position into oligonucleotides leads to a significant increase of duplex stability with complementary DNA and RNA. Here the synthesis of a novel G-clamp nucleoside analogue (G^8AE-clamp) bearing 2-aminoethyl tether at C8-atom is presented. Introduction of such modified residues into oligonucleotides lead to enhanced specificity of duplex formation towards complementary DNA and RNA targets with increased thermal and 3'-exonuclease stability. According to CD-spectroscopy studies G^8AE-clamp does not substantially disrupt helix geometry. Primers containing G^8AE-clamp demonstrated superior sensitivity in qPCR detection of dsRNA of Kemerovo virus in comparison to native oligonucleotides.