Synthetic oxetanes in drug discovery: where are we in 2025?

Oxetanes are increasingly prevalent motifs in medicinal chemistry. While oxetanes feature famously in the taxol family, it was not until the recent approval of rilzabrutinib that they have been validated in a fully synthetic drug. These four-membered oxygen-containing rings are valued for their ability to modulate key physicochemical properties such as polarity, lipophilicity, and metabolic stability. Their incorporation can improve aqueous solubility, reduce metabolic liability, reduce basicity of adjacent amines, and redirect metabolic clearance away from cytochrome P450 enzymes.

This review examines the role of the oxetane in nine clinical candidates, one very recently approved, two recently discontinued clinical candidates, two tool compounds, and three lead compounds disclosed in 2024. Recent advances indexed in SciFinder-n (2017-2024) in the process-scale and laboratory-scale synthetic routes are discussed, highlighting ongoing innovation required to access these motifs efficiently and sustainably.

The regulatory approval of rilzabrutinib and likely approval of ziresovir provide confidence in using oxetanes as important elements in drug design. While oxetanes have so far been incorporated primarily as pendant groups to optimize physicochemical properties, their use as scaffolding and binding elements presents an exciting opportunity. Enhanced synthetic accessibility to oxetane derivatives will expedite their inclusion in drug discovery campaigns.