LAUSR

Bridged nucleic acids (BNA) or locked nucleic acids (LNA) are a class of nucleic acids modification, which is obtained by connecting the 2'-O and 4'-C of ribose sugar using a methylene bridge. This ‘bridging or locking’ (hence the name) of ribose sugar has a tremendous impact both on the biological and biophysical properties of therapeutic nucleic acids. They have enhanced stability against nucleases and also have higher binding affinity for the target RNA. Owing to these advantages, BNA is one of the most preferred nucleic acid modifications of antisense oligonucleotides (ASOs). However, the synthesis of BNA monomers which are lengthy and low-yielding, requires extensive protection and deprotection of the sugar functionalities. In this article, we aim to review challenges associated with their synthesis, and discuss recent chemical, chemo-enzymatic, and transglycosylation strategies employed for efficient and cost-effective synthesis of BNA monomers and selected BNA analogues.