Utilizing o-Quinone Methide Chemistry: Synthesis of d₉-Ivacaftor

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).