Emerging strategies and innovations in circular RNA synthesis.

Circular RNAs (circRNAs) have emerged as a promising class of therapeutic molecules distinguished by their covalently closed topology, which provides exceptional exonuclease resistance, prolonged intracellular stability, and sustained protein expression. These properties, combined with reduced innate immunogenicity and capacity for cap-independent translation, position circRNAs as attractive candidates for vaccines, oncology therapeutics, and treatments for genetic and neurological disorders. Parallel advances in chemical biology have significantly expanded the synthetic toolkit for generating circRNAs, complementing traditional enzymatic ligation and ribozyme-based approaches with efficient chemical, chemoenzymatic, and bioorthogonal circularization strategies that enable scalable production and incorporation of diverse chemical modifications. This review integrates the biological roles of circRNAs with a comparative analysis of emerging synthetic methods, highlighting their mechanistic principles, advantages, and limitations. Advances in delivery platforms and multi-omics validation further strengthen the translational potential of engineered circRNAs as next-generation RNA therapeutics.