Unifying the synthesis of nucleoside analogs

Regioselective Deacetylation in Nucleosides and Derivatives

Nucleoside analogues are a promising class of natural compounds in the pharmaceutical industry, and many antiviral, antibacterial and anticancer drugs have been created through structural modification of nucleosides scaffold. Acyl protecting groups, especially the acetyl group, play an important role in the protection of hydroxy groups in nucleoside synthesis and modification; consequently, numerous methodologies have been put forth for the acetylation of free nucleosides. However, for nucleosides that contain different O- and N-based functionalities, selective deprotection of the acetyl group(s) in nucleosides has been studied little, despite its practical significance in simplifying the preparation of partially or differentially substituted nucleoside intermediates. In this mini-review, recent approaches for regioselective deacetylation in acetylated nucleosides and their analogues are summarized and evaluated. Different regioselectivities (primary ester, secondary ester, full de-O-acetylation, and de-N-acetylation) are summarized and discussed in each section.

Nucleoside Analogs: A Review of Its Source and Separation Processes

Nucleoside analogs play a crucial role in the production of high-value antitumor and antimicrobial drugs. Currently, nucleoside analogs are mainly obtained through nucleic acid degradation, chemical synthesis, and biotransformation. However, these methods face several challenges, such as low concentration of the main product, the presence of complex matrices, and the generation of numerous by-products that significantly limit the development of new drugs and their pharmacological studies. Therefore, this work aims to summarize the universal separation methods of nucleoside analogs, including crystallization, high-performance liquid chromatography (HPLC), column chromatography, solvent extraction, and adsorption. The review also explores the application of molecular imprinting techniques (MITs) in enhancing the identification of the separation process. It compares existing studies reported on adsorbents of molecularly imprinted polymers (MIPs) for the separation of nucleoside analogs. The development of new methods for selective separation and purification of nucleosides is vital to improving the efficiency and quality of nucleoside production. It enables us to obtain nucleoside products that are essential for the development of antitumor and antiviral drugs. Additionally, these methods possess immense potential in the prevention and control of serious diseases, offering significant economic, social, and scientific benefits to the fields of environment, biomedical research, and clinical therapeutics.

Practical and concise synthesis of nucleoside analogs

Nucleoside analogs are valuable commodities in the development of antisense oligonucleotides or as stand-alone antiviral and anticancer therapies. Syntheses of nucleoside analogs are typically challenged by a reliance on chiral pool starting materials and inefficient synthetic routes that are not readily amenable to diversification. The novel methodology described in this protocol addresses several longstanding challenges in nucleoside analog synthesis by enabling flexible and selective access to nucleoside analogs possessing variable nucleobase substitution, D- or L-configuration, selective protection of C3'/C5' alcohols and C2' or C4' derivatizations. This protocol provides direct access to C3'/C5' protected nucleoside analogs in three steps from simple, achiral starting materials and is described on both research (2.8 g) and process (30 g) scales for the synthesis of C3'/C5'-acetonide protected uridine. Using this protocol, proline catalyzes the fluorination of simple heteroaryl-substituted aldehyde starting materials, which are then directly engaged in a one-pot enantioselective aldol reaction with a dioxanone. Reduction, followed by intramolecular annulative fluoride displacement, forges the nucleoside analog. The three-step parent protocol can be completed in ~5 d by using simple mix-and-stir reaction procedures and standard column chromatographic purification techniques.

The practical acetylation of nucleosides using acetic anhydride/acetic acid as a reusable solvent

The highly practical acetylation of free nucleosides is achieved using acetic anhydride/acetic acid as a reusable solvent and acetylating regent. A series of nucleosides, including ribosyl, deoxyribosyl, arabinosyl, acyclic and pyranosyl, and many clinical drugs were acetylated efficiently, even on large scale (200 g).

Design, chemical synthesis and antiviral evaluation of 2'-deoxy-2'-fluoro-2'-C-methyl-4'-thionucleosides

Nucleoside analogues represent an historically accomplished class of antiviral drug. Notwithstanding this, new molecular scaffolds are required to overcome their limitations and evolve pharmacophore space within this established field. Herein, we develop concise synthetic access to a new 2'-deoxy-2'-fluoro-2'-C-methyl-4'-thionucleoside chemotype, including the ProTide form of the uridine analogue. Biological evaluation of these materials in the Hepatitis C replicon assay shows little activity for the canonical pyrimidine forms, but the phosphoramidate of 2'-deoxy-2'-fluoro-2'-C-methyl-β-d-4'-thiouridine has an EC₅₀ of 2.99 μM. Direct comparison to the established Hepatitis C drug Sofosbuvir shows a 100-fold drop in activity upon substituting the furanose chalcogen; the reasons for this are as yet unclear.

Fluorinated Nucleosides: Synthesis, Modulation in Conformation and Therapeutic Application

Over the last twenty years, fluorination on nucleoside has established itself as the most promising tool to use to get biologically active compounds that could sustain the clinical trial by affecting the pharmacodynamics and pharmacokinetic properties. Due to fluorine's inherent unique properties and its judicious introduction into the molecule, makes the corresponding nucleoside metabolically very stable, lipophilic, and opens a new site of intermolecular binding. Fluorination on various nucleosides has been extensively studied as a result, a series of fluorinated nucleosides come up for different therapeutic uses which are either approved by the FDA or under the advanced stage of the clinical trial. Here in this review, we are summarizing the latest development in the chemistry of fluorination on nucleoside that led to varieties of new analogs like carbocyclic, acyclic, and conformationally biased nucleoside and their biological properties, the influence of fluorine on conformation, oligonucleotide stability, and their use in therapeutics.

Chemical synthesis of 4'-thio and 4'-sulfinyl pyrimidine nucleoside analogues

Analogues of the canonical nucleosides required for nucleic acid synthesis have a longstanding presence and proven capability within antiviral and anticancer research. 4'-Thionucleosides, that incorporate bioisosteric replacement of furanose oxygen with sulfur, represent an important chemotype within this field. Established herein is synthetic capability towards a common 4-thioribose building block that enables access to thio-ribo and thio-arabino pyrimidine nucleosides, alongside their 4'-sulfinyl derivatives. In addition, this building block methodology is templated to deliver 4'-thio and 4'-sulfinyl analogues of the established anticancer drug gemcitabine. Cytotoxic capability of these new analogues is evaluated against human pancreatic cancer and human primary glioblastoma cell lines, with observed activities ranging from low μM to >200 μM; explanation for this reduced activity, compared to established nucleoside analogues, is yet unclear. Access to these chemotypes, with thiohemiaminal linkages, will enable a wider exploration of purine and triphosphate analogues and the application of such materials for potential resistance towards relevant hydrolytic enzymes within nucleic acid biochemistries.