Viscosity-Induced Emission of 5-(Diarylmethylene)imidazolone with Extended Conjugation via Attachment of N-Methylpyrrole at the 2-Position.

We have developed a series of 2-monoaryl-5-diarylmethylene analogs of the green fluorescent protein chromophore to study their viscosity-induced emission (VIE) properties. The analogs were synthesized by a condensation with methyl imidate and N-(diarylmethylene)glycinate. Among the analogs, the N-methylpyrrol-2-yl-substituted analog 1h induced the most remarkable VIE behavior in triglyceride and lipid bilayers probably due to the high π-electron-rich property of the pyrrole ring. The pyrrole substituent in imidazolone analogs can be expected to become a common template for introducing VIE behavior.

Nucleobase derivatives induce in-source decay of oligonucleotides as new matrix-assisted laser desorption/ionization matrices.

RATIONALE: For quality control of oligonucleotide therapeutics, accurate and efficient structural characterization using mass spectrometry techniques, such as liquid chromatography/mass spectrometry (LC/MS) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), is essential. In MALDI MS analysis, matrix selection is critical and a new matrix could enable more efficient and rapid structural analysis. METHODS: We hypothesized that nucleobase derivatives could act as matrices more efficiently than the currently used matrices for oligonucleotides because of structural similarity, which leads to close contact with the analyte. To evaluate their suitability as matrices, 16 nucleobase derivatives were selected and tested as matrix candidates for oligonucleotide analysis. RESULTS: Six of the 16 nucleobase derivatives acted as matrices for oligonucleotides. Particularly, 6-thioguanine (TG) performed well and induced clear in-source decay fragmentation. When TG or 2-amino-6-chloropurine was used as the matrix, oligonucleotides were ionized, and mainly the w and d fragment ions were observed. CONCLUSIONS: Herein we demonstrate that a 10-mer RNA or DNA sequence can be successfully characterized using TG as matrix and suggest the possibility of using nucleobase derivatives as novel matrices in oligonucleotide sequencing.

Different reactivity of Sp and Rp isomers of phosphorothioate-modified oligonucleotides in a duplex structure.

The presence of a stereoisomeric center at the phosphorus atom in phosphorothioate-modified oligonucleotides (PS-ONs) has been recognized as an important feature since the early stages of their development. Therefore, several studies have been conducted on the chirality of PS-ONs. In this study, we evaluated the stereo-biased chemistry of PS-ON duplexes. Depending on their absolute configurations, PS-ON duplexes were found to have significantly different and stereospecific reactivities towards simple alkylating reagent.

Synthesis and environment-dependent fluorescence behavior of a biaryl-conjugated (diphenylmethylene)imidazolinone.

The newly designed green fluorescent protein (GFP) chromophore analog, bar-DAIN, which has a 2-biaryl-conjugated 5-(diphenylmethylene)imidazolinone structure, was effectively synthesized using the Suzuki coupling reaction. Bar-DAIN showed environment-dependent fluorescence behavior; for example, the thienyl analog emitted yellow-green fluorescence in viscous solution (λem: 535 nm), yellow-orange fluorescence in suspension (λem: 551 nm), and cyan fluorescence in a powder state (λem: 497 nm) although it showed almost no emission in common solvents such as dichloromethane. The dynamic discoloration of the fluorescence was observed by changing environmental conditions from suspension to viscous.

Effective syntheses of 2',4'-BNANC monomers bearing adenine, guanine, thymine, and 5-methylcytosine, and the properties of oligonucleotides fully modified with 2',4'-BNANC.

We efficiently synthesized 2'-O,4'-C-aminomethylene-bridged nucleic acid (2',4'-BNANC) monomers bearing the four nucleobases, guanine, adenine, thymine, and 5-methylcytosine and incorporated these monomers into oligonucleotides. Initially, we carried out the transglycosylation reaction on several 2'-O-substituted 5-methyluridines to evaluate the effects of 2'-substitutions on this reaction. Under the optimized conditions, purine nucleobases were successfully introduced, and 2',4'-BNANC monomers bearing adenine or guanine were obtained over several steps. In addition, the improved synthesis of the 2',4'-BNANC monomers bearing thymine or 5-methylcytosine was also achieved. The obtained 2',4'-BNANC monomers were subsequently incorporated into oligonucleotides and the duplex-forming abilities of the modified oligonucleotides were investigated. Duplexes containing 2',4'-BNANC monomers in both or either strands were found to possess excellent thermal stabilities.

Synthesis and properties of geometrical 4-diarylmethylene analogs of the green fluorescent protein chromophore.

We have developed a novel analog of the GFP chromophore: geo-DAIN. Since geo-DAIN is equipped with an E/Z-photoisomerizable geometrical diarylmethylene moiety instead of benzylidene of the GFP chromophore, different-colored reversible emissions are expected. We synthesized geo-DAIN by a condensation with methyl imidate and N-(diarylmethylene)glycinate. We found the emission from geo-DAIN to be different from that of benzylidene-type analogs; in the powder state, the E- and Z-isomers of geo-DAIN emitted different fluorescence colors.

Synthesis and biophysical properties of 5'-thio-2',4'-BNA/LNA oligonucleotide.

Phosphorothioate modification of oligonucleotides is one of the most promising chemical modifications in nucleic acid therapeutics. Structurally similar 5'-thio or phosphorothiolate-modified nucleotides, in which the 5'-bridging oxygen atom is replaced with a sulfur atom, are attracting attention and gaining importance in oligonucleotide-based research. In our present study, we synthesized 5'-thio-2',4'-BNA/LNA monomers bearing thymine or 5-methylcytosine nucleobase. The 5'-thio-2',4'-BNA/LNA monomers were successfully incorporated into target oligonucleotides, and their nuclease stability and binding affinity with complementary strands were evaluated.

Considerations of the Japanese Research Working Group for the ICH S6 & Related Issues Regarding Nonclinical Safety Assessments of Oligonucleotide Therapeutics: Comparison with Those of Biopharmaceuticals.

This white paper summarizes the current consensus of the Japanese Research Working Group for the ICH S6 & Related Issues (WGS6) on strategies for the nonclinical safety assessment of oligonucleotide-based therapeutics (ONTs), specifically focused on the similarities and differences to biotechnology-derived pharmaceuticals (biopharmaceuticals). ONTs, like biopharmaceuticals, have high species and target specificities. However, ONTs have characteristic off-target effects that clearly differ from those of biopharmaceuticals. The product characteristics of ONTs necessitate specific considerations when planning nonclinical studies. Some ONTs have been approved for human use and many are currently undergoing nonclinical and/or clinical development. However, as ONTs are a rapidly evolving class of drugs, there is still much to learn to achieve optimal strategies for the development of ONTs. There are no formal specific guidelines, so safety assessments of ONTs are principally conducted by referring to published white papers and conventional guidelines for biopharmaceuticals and new chemical entities, and each ONT is assessed on a case-by-case basis. The WGS6 expects that this report will be useful in considering nonclinical safety assessments and developing appropriate guidelines specific for ONTs.

Evaluation of size-exclusion chromatography for the analysis of phosphorothioate oligonucleotides.

We evaluated size exclusion chromatography (SEC) for the detection of high-order structure of phosphorothioate oligonucleotides (PS-oligo). Because of strong interaction between PS-oligo and column packing material, peaks were broader and elution time was longer than those of the corresponding natural DNA oligonucleotides. However, single- and double-stranded structures of PS-oligo were clearly separated and discriminated, while single-stranded with high-order structures such as G-quadruplex and hairpin structure were not distinguished from each other.

In vitro and in vivo biophysical properties of oligonucleotides containing 5'-thio nucleosides.

Phosphorothioate modification is one of the most widely investigated and promising chemical modifications in oligonucleotide (ON) based therapeutics. Structurally similar 5'-thio or phosphorothiolate-modified nucleotides, in which a 5'-bridging oxygen is replaced with a sulfur atom, are gaining importance for ON-based research. Several reports have been published describing the synthesis of 5'-thio-modified ONs but no detailed in vitro and in vivo data are available. Here, we report the synthesis of 5'-thio-modified 2'-deoxy-5-methylcytidine. 5'-Thio-modified thymidine and 2'-deoxy-5-methylcytidine were incorporated into target ONs, then we evaluated their binding affinity, nuclease stability, RNase H mediated scission, stability in blood serum, and in vitro and in vivo activity. This is the first report showing the influence of 5'-thio-modified antisense ONs in in vitro and in vivo experiments.