Biocatalytic Nucleobase Diversification of 4'-Thionucleosides and Application of Derived 5-Ethynyl-4'-thiouridine for RNA Synthesis Detection.

Nucleoside and nucleotide analogues have proven to be transformative in the treatment of viral infections and cancer. One branch of structural modification to deliver new nucleoside analogue classes explores replacement of canonical ribose oxygen with a sulfur atom. Whilst biological activity of such analogues has been shown in some cases, widespread exploration of this compound class is hitherto hampered by the lack of a straightforward and universal nucleobase diversification strategy. Herein, we present a synergistic platform enabling both biocatalytic nucleobase diversification from 4'-thiouridine in a one-pot process, and chemical functionalization to access new entities. This methodology delivers entry across pyrimidine and purine 4'-thionucleosides, paving a way for wider synthetic and biological exploration. We exemplify our approach by enzymatic synthesis of 5-iodo-4'-thiouridine on multi-milligram scale and from here switch to complete chemical synthesis of a novel nucleoside analogue probe, 5-ethynyl-4'-thiouridine. Finally, we demonstrate the utility of this probe to monitor RNA synthesis in proliferating HeLa cells, validating its capability as a new metabolic RNA labelling tool.

Purine nucleoside antibiotics: recent synthetic advances harnessing chemistry and biology.

Covering: 2019 to 2023Nucleoside analogues represent one of the most important classes of small molecule pharmaceuticals and their therapeutic development is successfully established within oncology and for the treatment of viral infections. However, there are currently no nucleoside analogues in clinical use for the management of bacterial infections. Despite this, a significant number of clinically recognised nucleoside analogues are known to possess some antibiotic activity, thereby establishing a potential source for new therapeutic discovery in this area. Furthermore, given the rise in antibiotic resistance, the discovery of new clinical candidates remains an urgent global priority and natural product-derived nucleoside analogues may also present a rich source of discovery space for new modalities. This Highlight, covering work published from 2019 to 2023, presents a current perspective surrounding the synthesis of natural purine nucleoside antibiotics. By amalgamating recent efforts from synthetic chemistry with advances in biosynthetic understanding and the use of recombinant enzymes, prospects towards different structural classes of purines are detailed.

Preparation of a 4'-Thiouridine Building-Block for Solid-Phase Oligonucleotide Synthesis.

Starting from a commercially available thioether, we report a nine-step synthesis of a 4'-thiouridine phosphoramidite building-block. We install the uracil nucleobase using Pummerer-type glycosylation of a sulfoxide intermediate followed by a series of protecting group manipulations to deliver the desired phosphite. Notably, we introduce a 3',5'-O-di-tert-butylsilylene protecting group within a 4'-thiosugar framework, harnessing this to ensure regiospecific installation of the 2'-O-silyl protecting group. We envisage this methodology will be generally applicable to other 4'-thionucleosides and duly support the exploration of their inclusion within related nucleic acid syntheses. © 2023 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: (2R,3S,4R)-2,3-O-Isopopropylidene-5-O-tert-butyldiphenylsilyl-1-(4-sulfinyl)cyclopentane: Sulfoxidation Basic Protocol 2: 2',3'-O-Isopropylidene-5'-O-tert-butyldiphenylsilyl-4'-thiouridine: Pummerer glycosylation Basic Protocol 3: 4'-Thiouridine: Deprotection Basic Protocol 4: 2'-O-tert-Butyldimethylsilyl-3',5'-di-tert-butylsiloxy-4'-thiouridine: 2',3',5'-O-silylation Basic Protocol 5: 2'-O-tert-Butyldimethylsilyl-4'-thiouridine: Selective 3'-5'-desilylation Basic Protocol 6: 2'-O-tert-Butyldimethylsilyl-5'-O-dimethoxytrityl-4'-thiouridine: 5'-O-dimethoxytritylation Basic Protocol 7: 2'-O-tert-butyldimethylsilyl-3'-O-[(2-cyanoethoxy)(N,N-diisopropylamino)phosphino]-5'-O-dimethoxytrityl-4'-thiouridine: 3'-O-phosphitylation.

Synthesis of fluorinated carbocyclic pyrimidine nucleoside analogues.

Analogues of the canonical nucleosides have a longstanding presence and proven capability within medicinal chemistry and drug discovery research. The synthesis reported herein successfully replaces furanose oxygen with CF2 and CHF in pyrimidine nucleosides, granting access to an alternative pharmacophore space. Key diastereoselective conjugate addition and fluorination methodologies are developed from chiral pool materials, establishing a robust gram-scale synthesis of 6'-(R)-monofluoro- and 6'-gem-difluorouridines. Vital intermediate stereochemistries are confirmed using X-ray crystallography and NMR analysis, providing an indicative conformational preference for these fluorinated carbanucleosides. Utilising these 6'-fluorocarbauridine scaffolds enables synthesis of related cytidine, ProTide and 2'-deoxy analogues alongside a preliminary exploration of their biological capabilities in cancer cell viability assays. This synthetic blueprint offers potential to explore fluorocarbanucleoside scaffolds, indicatively towards triphosphate analogues and as building blocks for oligonucleotide synthesis.