Exploring Scope and Scale Limitations of a Modular Route to C4ʹ-Modified Nucleoside Analogues

C4ʹ-modified nucleoside analogues (NAs) continue to attract global attention for treating infectious diseases and as components in oligonucleotide therapeutics. Current preparations mostly employ lengthy semi-synthetic approaches that do not allow for the efficient exploration of the chemical space associated with this valuable nucleoside subclass. We previously reported a concise, modular synthesis of 4′-modified NAs based on an asymmetric aldol strategy, enabling the straightforward incorporation of a wide range of C4′ modifications and nucleobases. The route also provided access to both Land D-configured nucleosides, as well as Clinked analogues. Here, we explore the scope of this work by demonstrating the compatibility of four additional C4′ modifications and ten nucleobases, offering practitioners a clearer understanding of the scope, capabilities, and limitations of our methodology. Further, we detail the pilot-scale (250 mg) and process-scale (85 g) preparation of 4′-methyl-ribothymidine (4′,5-dimethyluridine), providing practical guidance on overcoming key synthetic pitfalls and on optimizing the methodology for new substrates.