Lead time and cost are important factors for any pharmaceutical API. However, these issues become even more important when the drug substance contains an isotope such as deuterium, which has a natural abundance of only ∼0.016% of all hydrogen. Fewer suppliers and logistical barriers both play a role in driving up the cost. These factors can challenge the supply route used to manufacture d9-ivacaftor (17), requiring investigation into alternative routes. By adapting the work from Pettus et al., a synthetic approach utilizing a transient o-quinone methide allowed access to the deuterium-labeled o-tert-butylphenol moiety. This was developed and proven on pilot scale to significantly reduce the number of deuterated reagents used, leading to an overall reduction in cost by a factor of 10, while also providing the substantial benefit of applying prior process knowledge from the parent, nonisotopically enriched API ivacaftor (7).

A strategy for the risk assessment of potentially genotoxic impurities is described that utilizes Quality by Design in an effort to furnish greater process and analytical understanding, ultimately leading to a determination of impurity criticality. By identifying the risks and parameters that most influence those risks, an enhancement of both product and process control is attained that mitigates the potential impact of these impurities. This approach calls for the use of toxicological testing where necessary, chemical fate arguments when possible, multivariate analyses to develop design space, and use of spiking data to support specifications. Strong analytical support, especially with the development of low-level detection methods, is critical. We believe that this strategy not only aids in the development of a robust API process but also delivers on the identification and subsequent mitigation of risks to a class of impurities that are of high interest in the field.