Engineering a Cytidine Aminotransferase for Biocatalytic Production of the Antiviral Molnupiravir

The COVID-19 pandemic highlights the urgent need for cost-effective processes to rapidly manufacture antiviral drugs at scale. Here we report a concise biocatalytic process for Molnupiravir, a nucleoside analogue currently in phase 3 clinical trials as an orally available treatment for SARS-CoV-2. Key to the success of this process was the development of a cytidine aminotransferase for the production of N-hydroxy-cytidine through evolutionary adaption of the hydrolytic enzyme cytidine deaminase. This engineered biocatalyst performs >100,000 turnovers in less than 30 minutes, operates at 180 g/L substrate loading and benefits from in situ crystallization of the N-hydroxy-cytidine product (>90% yield), which can be converted to Molnupiravir by a selective 5’-acylation using Novozym® 435.