Non-Catalyzed Click Reactions of ADIBO Derivatives with 5-Methyluridine Azides and Conformational Study of the Resulting Triazoles

Fluorine Labeling of ortho-Phenylenes to Facilitate Conformational Analysis

¹H NMR spectroscopy is a powerful tool for the conformational analysis of ortho-phenylene foldamers in solution. However, as o-phenylenes are integrated into ever more complex systems, we are reaching the limits of what can be analyzed by ¹H- and ¹³C-based NMR techniques. Here, we explore fluorine labeling of o-phenylene oligomers for analysis by ¹⁹F NMR spectroscopy. Two series of fluorinated oligomers have been synthesized. Optimization of monomers for Suzuki coupling enables an efficient stepwise oligomer synthesis. The oligomers all adopt well-folded geometries in solution, as determined by ¹H NMR spectroscopy and X-ray crystallography. ¹⁹F NMR experiments complement these methods well. The resolved singlets of one-dimensional ¹⁹F{¹H} spectra are very useful for determining relative conformer populations. The additional information from two-dimensional ¹⁹F NMR spectra is also clearly valuable when making ¹H assignments. The comparison of ¹⁹F isotropic shielding predictions to experimental chemical shifts is not, however, currently sufficient by itself to establish o-phenylene geometries.

Modular synthesis of amphiphilic chitosan derivatives based on copper-free click reaction for drug delivery

Amphiphilic chitosan derivatives have attracted wide attention as drug carriers due to their physicochemical properties. However, obtaining a desired amphiphilic chitosan derivative by tuning the various functional groups was complex and time-consuming. Therefore, a facile and common synthesis strategy would be promising. In this study, a modular strategy based on strain-promoted azide-alkyne cycloaddition (SPAAC) click reaction was designed and applied in synthesizing deoxycholic acid- or octanoic acid-modified N-azido propionyl-N,O-sulfate chitosan through tuning the hydrophobic groups. Additionally, chitosan derivatives with the same substitute groups were prepared via amide coupling as controls. We demonstrated that these derivates via the two strategies showed no obvious difference in physicochemical properties, drug loading ability and biosafety, indicating the feasibility of modular strategy. Notably, the modular strategy exhibited advantages including high reactivity, flexibility and reproducibility. We believe that this modular strategy could provide varied chitosan derivatives in an easy and high-efficiency way for improving multifunctional drug carriers.

Synthesis of 2'-C,4'-C-Methyleneoxy-Bridged Thymidine Derivatives and Properties of Modified Oligonucleotides

2',4'-Bridged nucleic acid (2',4'-BNA) analogues are used for therapeutic oligonucleotides, owing to their excellent hybridizing ability with complementary RNA and high resistance toward enzymatic degradation. We developed 2',4'-BNA analogues with oxygen atoms at 6'-positions (e.g., EoNA and EoDNAs) and demonstrated that the presence of 6'-oxygen atoms in the bridge structure could show positive effect on the properties of the modified oligonucleotides. Herein, we designed and synthesized 7'-methyl derivatives of methyleneoxy-bridged 2'-deoxyribonucleic acid (MoDNA), possessing a five-membered bridge with 6'-oxygen atom via radical cyclization for the bridge construction. The synthesized monomers were incorporated into the oligonucleotides by solid-phase oligonucleotide synthesis. The MoDNA-modified oligonucleotides showed high affinity toward single-stranded RNA and double-stranded DNA, as well as excellent resistance toward nuclease compared with the corresponding natural oligonucleotide.

2'-C,4'-C-Ethyleneoxy-Bridged 2'-Deoxyribonucleic Acids (EoDNAs) with Thymine Nucleobases: Synthesis, Duplex-Forming Ability, and Enzymatic Stability

This chapter describes procedures for (1) the synthesis of six 2'-C,4'-C-ethyleneoxy-bridged thymidine phosphoramidites, i.e., methylene-EoDNA-T, (R)-Me-methylene-EoDNA-T, (S)-Me-methylene-EoDNA-T, EoDNA-T, (R)-Me-EoDNA-T, and (S)-Me-EoDNA-T phosphoramidites, (2) the introduction of the phosphoramidites into oligonucleotides, (3) UV-melting experiments of the duplexes of the modified oligonucleotides and complementary RNA, and (4) nuclease degradation experiments of the modified oligonucleotides.

Synthesis of 8-(1,2,3-triazol-1-yl)-7-deazapurine nucleosides by azide-alkyne click reactions and direct C-H bond functionalization

Treatment of toyocamycin or sangivamycin with 1,3-dibromo-5,5-dimethylhydantoin in MeOH (r.t./30 min) gave 8-bromotoyocamycin and 8-bromosangivamycin in good yields. Nucleophilic aromatic substitution of 8-bromotoyocamycin with sodium azide provided novel 8-azidotoyocamycin. Strain promoted click reactions of the latter with cyclooctynes resulted in the formation of the 1,2,3-triazole products. Iodine-mediated direct C8-H bond functionalization of tubercidin with benzotriazoles in the presence of tert-butyl hydroperoxide gave the corresponding 8-benzotriazolyltubercidin derivatives. The 8-(1,2,3-triazol-1-yl)-7-deazapurine derivatives showed moderate quantum yields and a large Stokes shifts of ~ 100 nm.

Study and application of noncatalyzed photoinduced conjugation of azides and cycloocta-1,2,3-selenadiazoles

The non-catalyzed cycloaddition of eight structurally different azides with cyclooctyne generated in situ by the photolysis of cycloocta-1,2,3-selenadiazole gives 1,2,3-triazole derivatives as the main products.